CHAPTER VIII
SYSTEMATIC
I. CLASSIFICATION
A. WORK OF SUCCESSIVE SYSTEMATISTS
Since the time when lichens were first recognized as a separate class—as members of the genus Lichen by Tournefort[1016] or as “Musco-fungi” by Morison[1017],—many schemes of classification have been outlined, and the history of the science of lichenology, as we have seen, is a record of attempts to understand their puzzling structure, and to express that understanding by relating them to each other and to allied classes of plants. The great diversity of opinion in regard to their affinities is directly due to their composite nature.
_a._ DILLENIUS AND LINNAEUS. The first systematists were chiefly impressed by their likeness to mosses, hepatics or algae. Dillenius[1018] in the _Historia Muscorum_ grouped them under the moss genera:—IV. _Usnea_, V. _Coralloides_ and VI. _Lichenoides_. Linnaeus[1019] classified them among algae under the general name _Lichen_, dividing them into eight orders based on thalline characters in all but one instance, the second order being distinguished from the first by bearing scutellae. The British botanists of the latter part of the eighteenth century—Hudson, Lightfoot and others—were content to follow Linnaeus and in general adopted his arrangement.
_b._ ACHARIUS. Early in the nineteenth century Acharius, the Swedish Lichenologist, worked a revolution in the classification of lichens. He gave first place to the form of the thallus, but he also noted the fundamental differences in fruit-formation: his new system appeared in the _Methodus Lichenum_[1020] with an introduction explaining the terms he had introduced, many of them in use to this day.
Diagnoses of twenty-three genera are given with their included species. The work was further extended and emended in _Lichenographia Universalis_[1021] and in the _Synopsis Lichenum_[1022]. In his final arrangement the family “Lichenes” is divided into four classes, three of which are characterized solely by apothecial characters; the fourth class has no apothecia. They are as follows:
Class I. Idiothalami with three orders, Homogenei, Heterogenei and Hyperogenei: the apothecia differ in texture and colouration from the thallus: _Lecidea_, _Opegrapha_, _Gyrophora_, etc.
Class II. Coenothalami, with three orders, Phymaloidei, Discoidei and Cephaloidei. The apothecia are partly formed from the thallus: _Lecanora_, _Parmelia_, etc. The Pyrenolichens are also included by him in this class, because “the thallus surrounds and is concrete with the partly or wholly immersed apothecia.”
Class III. Homothalami with two orders, Scutellati and Peltati. The apothecia are formed from the cortical and medullary tissue of the thallus: _Ramalina_, _Usnea_, _Collema_, etc.
Class IV. Athalami, with but one sterile genus, _Lepraria_.
The orders are thus based on the form of the fruit; the genera in the _Synopsis_ number 41. Large genera such as _Lecanora_ with 132 species are divided into sections, many of which have in turn been established as genera, by S. F. Gray in 1821, and later by other systematists.
The _Synopsis_ was the text-book adopted by succeeding botanists for some 40 years with slight alterations in the arrangement of classes, genera, etc.
Wallroth[1023] and Meyer[1024] followed with their studies on the lichen thallus, and Wallroth’s division into “Homoiomerous” and “Heteromerous” was accepted as a useful guide in the maze of forms, representing as it did a great natural distinction.
_c._ SCHAERER. This valiant lichenologist worked continuously during the first half of the nineteenth century, but with very partial use of the microscope. His last publication in 1850, an _Enumeration of Swiss Lichens_, was the final declaration of the older school that relied on field characters. His classification is as follows:
Class I. Lichenes Discoidei, with ten orders from Usneacei to Graphidei; fruits open.
Class II. Lichenes Capitati, with three orders: Calicioidei, Sphaerophorei and Cladoniacei; fruits stalked.
Class III. Lichenes Verrucarioidei, with three orders: Verrucarii, Pertusarii and Endocarpei: fruits closed.
An “Appendix” contains descriptions of Crustacei and Fruticulosi, all sterile forms, except _Coniocarpon_ and _Arthonia_, which seem out of place, and finally a “Corollarium” of gelatinous lichens all classified under one genus _Collema_.
_d._ MASSALONGO AND KOERBER. As a result of their microscopic studies, these two workers proposed many changes based on fruit and spore characters, and Koerber in the _Systema Lichenum Germaniae_ (1855) gave expression to these views in his classification. He also made use of Wallroth’s distinctions of “homoiomerous” and “heteromerous,” thus dividing lichens at the outset into those mostly with blue-green and those with bright-green gonidia.
The following is the main outline of Koerber’s classification:
Series I. Lichenes Heteromerici. Order I. Lich. Thamnoblasti (fruticose). Order II. Lich. Phylloblasti (foliose). Order III. Lich. Kryoblasti (crustaceous). Series II. Lichenes Homoeomerici. Order IV. Lich. Gelatinosi. Order V. Lich. Byssacei.
With the exception of Order V all are subdivided into two sections, “gymnocarpi” with open fruits and “angiocarpi” with closed fruits, a distinction that had long been recognized both in lichens and in fungi.
_e._ NYLANDER. The above writers had been concerned with the interrelationships of lichens; Nylander, who was now coming forward as a lichenologist of note, gave a new turn to the study by dwelling on their relation to other classes of plants. Without for a moment conceding that they were either algal or fungal, he yet insisted on their remarkable affinity to algae on the one hand, and to fungi on the other, and he sought to make evident this double connection by his very ingenious scheme of classification[1025]. He began with what we may call “algal lichens,” those associated with blue-green gonidia in the family “Collemacei”; he continued the series to the most highly evolved foliose forms and then wound up with those that are most akin to fungi, that is, those with least apparent thalline formation—according to him—the “Pyrenocarpei.”
In his scheme, which is the one followed by Leighton and Crombie, the “family” represents the highest division; series, tribe, genus and species come next in order. We have thus:
Fam. I. Collemacei. Fam. II. Myriangiacei (now reckoned among fungi). Fam. III. Lichenacei.
This last family, which includes the great bulk of lichens, is divided into the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei; IV. Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up to the Phyllodei, or foliaceous lichens, which he considers higher in development than the fruticose or filamentous Ramalodei. The Placodei include four tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei and Graphidei. The classification is almost wholly based on thalline form, except for the Pyrenodei in which are represented genera with closed fruits, there being one tribe only, the Pyrenocarpei.
Nylander claims however to have had regard equally to the reproductive system and was the first to give importance to the spermogonia. The classification is coherent and easy to follow, though, like all classifications based on imperfect knowledge, it is not a little artificial; also while magnifying the significance of spermogonia and spermatia, he overlooked the much more important characters of the ascospores.
_f._ MÜLLER(-ARGAU). In preparing his lists of Genevan lichens (1862), Müller realized that Nylander’s series was unnatural, and he found as he studied more deeply that lichens must be ranged in parallel or convergent but detached groups. He recognized three main groups:
1. Eulichens, divided into Capitularieae, Discocarpeae and Verrucaroideae. 2. Epiconiaceae. 3. Collemaceae.
He suggested that, in relation to other plants, Eulichens approach Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with Lycoperdaceae, while Collemaceae are allied to the algal family Nostocaceae. These three groups of Eulichens, he held, advanced on somewhat parallel lines, but reached a very varied development, the Discocarpeae attaining the highest stage of thalline form. Müller accepted as characters of generic importance the form and structure of the fruiting body, the presence or absence of paraphyses, and the septation, colour, etc. of the spores.
A few years later (1867) the composite nature of the lichen thallus was announced by Schwendener, and, after some time, was acknowledged by most botanists to be in accordance with the facts of nature. Any system of classification, therefore, that claims to be a natural one, must, while following as far as possible the line of plant development, take into account the double origin of lichens both from algae and fungi, the essential unity and coherence of the class being however proved by the recurring similarity between the thalline types of the different phyla. As Müller had surmised: “they are a series of parallel detached though convergent groups.”
_g._ REINKE. The arrangement of Ascolichens on these lines was first seriously studied by Reinke[1026], and his conclusions, which are embodied[1027] in the _Lichens of Schleswig-Holstein_, have been largely accepted by succeeding workers. He recognizes three great subclasses: 1. Coniocarpi; 2. Discocarpi; 3. Pyrenocarpi.
The Coniocarpi are a group apart, but as their fruit is at first entirely closed—at least in some of the genera—the more natural position for them is between Discocarpi and Pyrenocarpi. It is in the arrangement of the Discocarpi that variation occurs. Reinke’s arrangement of orders and families in that sub-class is as follows:
Subclass 2. Discocarpi.
Order I. _GRAMMOPHORI_: Fam. _GRAPHIDACEI_ and _XYLOGRAPHACEI_.
Order II. _LECIDEALES_: Fam. _GYALECTACEI_, _LECIDEACEI_, _UMBILICARIACEI_ and _CLADONIACEI_.
Order III. _PARMELIALES_: Fam. _URCEOLARIACEI_, _PERTUSARIACEI_, _PARMELIACEI_, _PHYSCIACEI_, _TELOSCHISTACEI_ and _ACAROSPORACEI_.
Order IV. _CYANOPHILI_: Fam. _LICHINACEI_, _EPHEBACEI_, _PANNARIACEI_, _STICTACEI_, _PELTIGERACEI_, _COLLEMACEI_ and _OMPHALARIACEI_.
The orders represent generally the principal phyla or groups, the families subordinate parallel phyla within the orders. The first three orders are stages of advance as regards fruit development; the Cyanophili are a group apart.
Wainio[1028] rendered great service to Phylogeny in his elaborate work on Cladoniaceae, the most complicated of all the lichen phyla. He also drew up a scheme of arrangement in his work on Brazil Lichens[1029]. There is in it some divergence from Reinke’s arrangement, as he tends to give more importance to the thallus than to fruit characters as a guide. He places, for instance, Gyrophorei beside Parmelei and at a long distance from his Lecidei. The Cyanophili group of families he has interpolated between _Buelliae_ (Physciaceae) and _Lecideae_. Many workers approve of Wainio’s classification but it presents some difficult problems.
_h._ ZAHLBRUCKNER. The systematist of greatest weight in recent times is A. Zahlbruckner, who is responsible for the systematic account of lichens in Engler and Prantl’s _Natürlichen Pflanzenfamilien_. It is difficult to express the very great service he has rendered to Lichenology, in that and other world-wide studies of lichens. The sketch of lichen phylogeny as given in the present volume owes a great deal to the sound and clear guidance of his work, though his conclusions may not always have been accepted. The classification in the _Pflanzenfamilien_ is the one now generally followed.
The class _Lichenes_ is divided by Zahlbruckner[1030] into two subclasses, I. Ascolichens and II. Hymenolichens. He gives a third class, Gasterolichens[1031], but as it was founded on error[1032], it need not concern us here. The Ascolichens are by far the more important. These are subdivided into:
Series 1. =PYRENOCARPEAE=, with perithecial fruits. Series 2. =GYMNOCARPEAE=, with apothecial fruits.
These are again broken up into families, and in the arrangement and sequence of the families Zahlbruckner indicates his view of development and relationship. They occur in the following order:
SERIES 1. =PYRENOCARPEAE=
ALGAL CELLS PROTOCOCCACEAE OR _PALMELLA_.
I. _MORIOLACEAE._ } } II. _EPIGLOEACEAE._ } Thallus crustaceous, perithecia solitary. } III. _VERRUCARIACEAE._ }
IV. _DERMATOCARPACEAE._ Thallus squamulose or foliose.
V. _PYRENOTHAMNIACEAE._ Thallus fruticose. ALGAL CELLS _PRASIOLA_.
VI. _MASTOIDIACEAE._ ALGAL CELLS _TRENTEPOHLIA_.
VII. _PYRENULACEAE._ } } Thallus crustaceous, perithecia occurring VIII. _PARATHELIACEAE._ } singly.
IX. _TRYPETHELIACEAE._ } } Thallus crustaceous, perithecia united X. _ASTROTHELIACEAE._ } (stromatoid).
XI. _MYCOPORACEAE._ Thallus crustaceous, perithecia in compact groups with a common outer wall.
XII. _PHYLLOPYRENIACEAE._ Thallus minutely foliose. ALGAL CELLS _PHYLLACTIDIUM_ OR _MYCOIDEA_.
XIII. _STRIGULACEAE._ Tropical leaf-lichens. ALGAL CELLS _NOSTOC_ OR _SCYTONEMA_.
XIV. _PYRENIDIACEAE._ Thallus minutely squamulose or fruticose.
SERIES 2. =GYMNOCARPEAE=
Subseries 1. Coniocarpineae, with subperithecial fruits. Subseries 2. Graphidineae, with elongate, narrow fruits. Subseries 3. Cyclocarpineae, with round open fruits.
SUBSERIES 1. =CONIOCARPINEAE=
This is a well-defined group, peculiar in the disappearance of the asci at an early stage so that the spores lie like a powder in the globose partly closed fruits. Algal cells, bright-green; Protococcaceae. There are only three families:
XV. _CALICIACEAE._ Thallus crustaceous, apothecia stalked.
XVI. _CYPHELIACEAE._ Thallus crustaceous, apothecia sessile.
XVII. _SPHAEROPHORACEAE._ Thallus foliose or fruticose, apothecia sessile.
SUBSERIES 2. =GRAPHIDINEAE=
This subseries comes next in the form of fruit development; generally the apothecia are elongate, with a narrow slit-like opening, so that a transverse section shows almost a perithecial outline. Algal cells are mostly _Trentepohlia_.
XVIII. _ARTHONIACEAE._ Thallus crustaceous, apothecia oval or linear, flat.
XIX. _GRAPHIDACEAE._ Thallus crustaceous, apothecia linear, raised.
XX. _CHIODECTONACEAE._ Thallus crustaceous, apothecia generally immersed in a stroma.
XXI. _DIRINACEAE._ Thallus crustaceous, corticate above, apothecia round.
XXII. _ROCCELLACEAE._ Thallus fruticose, apothecia round or elongate.
SUBSERIES 3. =CYCLOCARPINEAE=
A large and very varied group! In most of the families the algal cells are bright-green (Chlorophyceae), in some they are blue-green (Cyanophyceae), these latter corresponding to Reinke’s order Cyanophili. The apothecia, as the name implies, are round and open; the “Cyanophili” have been placed by Zahlbruckner after those families in which the apothecium has no thalline margin. They form a phylum distinct from those that precede and those that follow.
The first family of the Cyclocarpineae, the Lecanactidaceae, is often placed under Graphidineae; in any case it forms a link between the two subseries.
1. _Lecideine group_ (apothecia without a thalline margin).
XXIII. _LECANACTIDACEAE._ Thallus crustaceous. Algal cells _Trentepohlia._ Apothecium with carbonaceous hypothecium or parathecium.
XXIV. _PILOCARPACEAE._ Thallus crustaceous. Algal cells Protococcaceae. Apothecia with a dense rather dark hypothecium.
XXV. _CHRYSOTHRICACEAE._ Thallus felted, loose in texture. Algal cells _Palmella_, Protococcaceae or _Trentepohlia_. Apothecia with or without a thalline margin. The affinity of the “Family” seems to be with Pilocarpaceae.
XXVI. _THELOTREMACEAE._ } Thallus crustaceous. Algal cells in the XXVII. _DIPLOSCHISTACEAE._ } first _Trentepohlia_; in the second } Protococcaceae. In both there are } prominent double margins round the } apothecium.
XXVIII. _ECTOLECHIACEAE._ Thallus very primitive in type. Algal cells Protococcaceae. Apothecia with or without a thalline margin. Nearly related to Chrysothricaceae.
XXIX. _GYALECTACEAE._ Thallus crustaceous. Algal cells _Trentepohlia_, _Phyllactidium_ or rarely _Scytonema_. Apothecia biatorine, _i.e._ of soft consistency and without gonidia.
XXX. _COENOGONIACEAE._ Thallus confusedly filamentous (byssoid). Algal cells _Trentepohlia_ or _Cladophora_. Apothecia biatorine.
XXXI. _LECIDEACEAE._ Thallus crustaceous or squamulose. Algal cells Protococcaceae. Apothecia biatorine (soft), or lecideine (carbonaceous).
XXXII. _PHYLLOPSORACEAE._ Thallus squamulose or foliose. Algal cells Protococcaceae. Apothecia biatorine or lecideine.
XXXIII. _CLADONIACEAE._ Thallus twofold. Algal cells Protococcaceae. Apothecia biatorine or lecideine.
XXXIV. _GYROPHORACEAE._ Thallus foliose. Algal cells Protococcaceae. Apothecia lecideine.
XXXV. _ACAROSPORACEAE._ Thallus primitive crustaceous, squamulose or foliose. Algal cells Protococcaceae. Apothecia with or without a thalline margin; very various, but always with many-spored asci.
2. _Cyanophili group._
In this group the classification depends almost entirely on the nature of the algal constituents. The apothecia are in most genera provided with a thalline margin.
_a. More or less gelatinous when moist._
XXXVI. _EPHEBACEAE._ Algal cells _Scytonema_ or _Stigonema_. Thallus minutely fruticose or filamentous.
XXXVII. _PYRENOPSIDACEAE._ Algal cells _Gloeocapsa_ (_Gloeocapsa_, _Xanthocapsa_ or _Chroococcus_). Thallus crustaceous, minutely foliose or fruticose.
XXXVIII. _LICHINACEAE._ Algal cells _Rivularia_. Thallus crustaceous, squamulose or minutely fruticose.
XXXIX. _COLLEMACEAE._ Algal cells _Nostoc_. Thallus crustaceous, minutely fruticose, or squamulose to foliose.
XL. _HEPPIACEAE._ Algal cells _Scytonema_. Thallus generally squamulose and formed of plectenchyma.
_b. Not gelatinous when moist._
XLI. _PANNARIACEAE._ Algal cells _Nostoc_, _Scytonema_ or rarely bright-green, Protococcaceae. Thallus crustaceous, squamulose or foliose.
XLII. _STICTACEAE._ Algal cells _Nostoc_ or Protococcaceae. Thallus foliose, and very highly developed, corticate on both surfaces.
XLIII. _PELTIGERACEAE._ Algal cells _Nostoc_ or Protococcaceae. Thallus foliose, corticate above.
3. _Lecanorine group_ (apothecia with a thalline margin).
The remaining families have all bright-green gonidia and nearly always apothecia with a thalline margin. The group includes several distinct phyla:
XLIV. _PERTUSARIACEAE._ Thallus crustaceous. Apothecia, one or several immersed in thalline tubercles; spores mostly very large.
XLV. _LECANORACEAE._ Thallus crustaceous or squamulose. Apothecia mostly superficial.
XLVI. _PARMELIACEAE._ Thallus foliose, rarely almost fruticose or filamentous. Apothecia scattered over the surface or marginal, sessile.
XLVII. _USNEACEAE._ Thallus fruticose or filamentous. Apothecia sessile or shortly stalked.
XLVIII. _CALOPLACACEAE._ Thallus crustaceous, squamulose or minutely fruticose. Apothecia with polarilocular colourless spores.
XLIX. _TELOSCHISTACEAE._ Thallus foliose or fruticose. Apothecia with polarilocular colourless spores.
L. _BUELLIACEAE._ Thallus crustaceous or squamulose. Apothecia (lecideine or lecanorine) with two-celled, thick-walled brown spores (polarilocular in part).
LI. _PHYSCIACEAE._ Thallus foliose, rarely partly fruticose. Apothecia with two-celled thick-walled brown spores (polarilocular in part).
Subclass 2. Hymenolichens.
There are only three closely related genera of Hymenolichens, _Cora_, _Corella_ and _Dictyonema_ with _Chroococcus_ or _Scytonema_ algae.
There is reason to dissent from the arrangement in one or two instances which will be pointed out in the following examination of families and genera.
B. FAMILIES AND GENERA OF ASCOLICHENS
The necessity for a well-reasoned and well-arranged system of classification is self-evident: without a working knowledge of the plants that are the subject of study no progress can be made. The recognition of plants as isolated individuals is not sufficient, it must be possible to place them in relation to others; hence the importance of a natural system. In identifying species artificial aids, such as habitat and substratum, are also often of great value, and a good working system should take account of all characteristics.
Lichen development is the result of two organisms mutually affecting each other, but as the fungus provides the reproductive system, it is the dominant partner: the main lines of classification are necessarily determined by fruit characters. The algae occupy a subsidiary position, but they also are of importance in shaping the form and structure of the thallus. The different phyla are often determined by the presence of some particular alga; it is in the delimitation of families that the algal influence is of most effect.
Zahlbruckner’s system gives due weight to the inheritance from both fungus and alga with, however, the fungus as the chief factor in development, and as his work is certain to be generally followed by modern lichenologists, it is the one of most immediate interest. His scheme has been accepted in the following more detailed account of families and genera, and for the benefit of home workers those that have not so far been recorded from the British Isles have been marked with an asterisk.
It cannot be affirmed that nomenclature is as yet firmly established in lichenology. Both on historical grounds and on those of convenience, the subject is one of extreme importance, and interest in it is one of the main avenues by which we secure continuity with the past, and by which we are able to realize not only the difficulty, but the romance of pioneer work. Besides, there can be no exchange of opinion between students nor assured knowledge of plants, until the names given to them are beyond dispute. According to the ruling of the Brussels Botanical Congress in 1910, Linnaeus’s[1033] list of lichens in the _Species Plantarum_ has been selected as the basis of nomenclature, but since his day many new families, genera and species have been described and often insufficiently delimited. It is not easy to decide between priority, which appeals to the historical sense, and recent use which is the plea of convenience. Here also it seems there can be no rigid decision; the one aim should be to arrive at a conclusion satisfactory to all, and accepted by all.
In the following necessarily brief account of families and genera, the “spermogonia” or “pycnidia” have in most cases been left out of account, as in many instances they vary within the family and occasionally even within the genus. Their taxonomic value is not without importance, but, in the general systematic arrangement, they are only subsidiary characters. An account of them has already been given, and for more detailed statements the student is referred to purely systematic works.
There are two main types of spore production in the “pycnidia” which have been shortly described by Steiner[1034] as “exobasidial” and “endobasidial.” In the former the sporophores are simple or branched filaments, at the apices of which a short process grows out and buds off a pycnidiospore; in the latter the spores are budded directly from cells lining the walls or filling the cavity of the pycnidium. The exobasidial type is more simply rendered in the following pages by “acrogenous,” the endobasidial by “pleurogenous” spore production. In many cases the “spermogonia” or “pycnidia” are still imperfectly known. In designating the gonidial algae, the more comprehensive Protococcaceae has been substituted for _Protococcus_, as in many cases the alga is probably not _Protococcus_ as now understood, but some other genus of the family[1035].
SUBCLASS I. ASCOLICHENS
SERIES I. PYRENOCARPINEAE
It is on mycological grounds that Pyrenocarpineae are placed at the base of lichen classification. There is no evidence that the series was first in time.
I. _MORIOLACEAE_
This family was described by Norman[1036] in 1872 from specimens collected by himself in Norway or in the Tyrol, on soil or more frequently on trees. There seems to have been no further record, and Zahlbruckner, while accepting the family, suggests that an examination or revision may be necessary.
The thallus is crustaceous. The algal cells, Protococcaceae, occur either in groups (sometimes stalked) surrounded by a plectenchymatous wall and called by Norman “goniocysts,” or they form nests in the thallus termed “nuclei” which are surrounded by a double wall of plectenchyma, colourless in the interior and brown outside. Norman invented the term “Allelositismus,” which may be rendered “mutualism,” to indicate this peculiar form of thallus. The species of _Spheconisca_ are fairly numerous on poplars, willows and conifers:
Algae in “goniocysts” 1. *Moriola Norm.[1037] Algae in double-walled “nuclei” 2. *Spheconisca Norm.
II. _EPIGLOEACEAE_
The family consists of but one genus and one species, _Epigloea bactrospora_, and, according to Zahlbruckner, further examination is necessary to make certain as to the lichenoid nature of the plant.
Zukal[1038] found the perithecia scattered over the leaves of mosses, and he alleges that hyphae connected with the perithecium were closely associated with the alga, _Palmella botryoides_, and were causing it no harm. Along with the perithecia he also found minute pycnidia. The “thallus” is of a gelatinous nature and homoiomerous in structure; the perithecia are soft and clear-coloured with many-spored asci and colourless one-septate spores.
The small globose pycnidia contain simple sporophores and acrogenous straight or slightly bent rod-like spores.
Asci many-spored; spores one-septate 1. *Epigloea Zukal.
III. _VERRUCARIACEAE_
In all the genera of this family the thallus is crustaceous, and, with very few exceptions, the species are saxicolous or terricolous. The thallus is variable within the crustaceous limits, and may be superficial and very conspicuous, almost imperceptible, or wholly immersed in the substratum. The algal cells are Protococcaceae, and in two of the genera the green cells penetrate the hymenium and grow in rows alongside of the asci. The perithecia are small roundish structures scattered over the thallus, the base immersed, but the upper portion generally projecting. An outer dark-coloured wall surrounds the whole perithecium (entire) or only the upper exposed portion (dimidiate); it opens above by a pore or ostiole more or less prominent.
In some of the genera the paraphyses become dissolved at an early stage, and somewhat similar filaments near the ostiole, termed periphyses, aid in the expulsion of the spores. The spores vary in septation, colour and size, and these variations have served to delimit the genera which have been formed from the original very large genus _Verrucaria_. The ascus may be 1-, 2-, 4- or 8-spored. In only one genus is it many-spored (_Trimmatothele_).
The genera are as follows:
Perithecia with simple ostioles. Paraphyses disappearing early, or wanting. Spores simple, ellipsoid 1. Verrucaria Web. Spores simple, elongate vermiform 2. Sarcopyrenia Nyl. Spores simple, numerous in the ascus 3. *Trimmatothele Norm. Spores 1-3-septate 4. Thelidium Massal. Spores muriform (with transverse and longitudinal divisions). Without hymenial gonidia 5. Polyblastia Massal. With hymenial gonidia 6. Staurothele Norm. Paraphyses present. Spores simple. Without hymenial gonidia 7. Thrombium Wallr. With hymenial gonidia 8. *Thelenidia Nyl. Spores 3-septate, broadly ellipsoid 9. *Geisleria Nitschke. Spores acicular, many-septate 10. Gongylia Koerb. Spores muriform 11. Microglaena Lönnr. Perithecia with a wide ring round the ostiole. Spores muriform; paraphyses unbranched 12. *Aspidothelium Wain. Spores elongate, many-septate; paraphyses branched 13. *Aspidopyrenium Wain.
IV. _DERMATOCARPACEAE_
In this family there is a much more advanced thalline development—generally squamulose or with some degree of foliose structure, though in the genus _Endocarpon_, some of the species are little more than crustaceous. The gonidia are bright-green Protococcaceae (according to Chodat, _Coccobotrys_ in _Dermatocarpon_). In _Endocarpon_ they appear in the hymenium.
The least developed in structure is _Normandina_: the thallus of the single species consists of delicate shell-like squamules which are non-corticate above and below. In the other genera there is a cortex of plectenchyma.
The perithecia are almost wholly immersed, and open above by a straight ostiole. The fructification of _Dacampia_ is considered by some lichenologists to be only a parasite on the white thickish squamulose thallus with which it is associated.
Hymenial gonidia present. Spores muriform 1. Endocarpon Hedw. Hymenial gonidia absent. Thallus non-corticate 2. Normandina Wain. Thallus corticate. Spores simple, colourless 3. Dermatocarpon Eschw. Spores simple, brown 4. *Anapyrenium Müll.-Arg. Spores elongate-septate, colourless 5. *Placidiopsis Beltr. Spores elongate-septate, brown 6. *Heterocarpon Müll.-Arg. Spores muriform, colourless 7. *Psoroglaena Müll.-Arg. Spores muriform, brown 8. Dacampia Massal.
V. _PYRENOTHAMNIACEAE_
Thallus more or less fruticose and corticate on both surfaces. Algal cells Protococcaceae.
Only two genera are included in this family: _Nylanderiella_ with one species from New Zealand, with a small laciniate thallus up to 15 mm. in height, partly upright, partly decumbent, and attached to the substratum by basal rhizinae; the other small genus, _Pyrenothamnia_, belongs to N. America; the thallus has a short rounded stalk which expands above to an irregular frond. The perithecia are immersed in the fronds.
Spores colourless, 1-septate 1. *Nylanderiella Hue[1039]. Spores brown, muriform 2. *Pyrenothamnia Tuckerm.
VI. _MASTOIDEACEAE_
A family containing one genus and one species, with a wide distribution, having been found in Siberia, on the Antarctic continent (Graham’s Land), as also in Tierra del Fuego, South Georgia, South Shetland Islands and Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae. Algal cells _Prasiola_[1040]. The perithecia are globose and partly project from the thallus; the asci are 8-spored; the paraphyses are mucilaginous and partly dissolving.
Spores elongate-fusiform, simple, colourless 1. *Mastoidea Hook. and Harv.
VII. _PYRENULACEAE_
This family of crustaceous lichens differs from Verrucariaceae chiefly in the gonidium which is a species of _Trentepohlia_. Genera and species are largely corticolous and the thallus is inconspicuous, often developing within the substratum. The perithecia, like those of _Verrucariae_, are immersed or partly emergent and have an entire or dimidiate outer wall. They are scattered over the thallus except in _Anthracothecium_ where they are often coalescent. This genus is tropical or subtropical except for one species which inhabits S.W. Ireland.
Paraphyses are variable, and in some species tend to disappear, but do not dissolve in mucilage. The spores are generally colourless, only in one monotypic genus, _Coccotrema_, are they simple. The cells into which the spore is divided differ in form according to the genus.
Paraphyses branched and entangled or wanting. Perithecia opening above by stellate lobes 1. *Asteroporum Müll.-Arg. Perithecia opening by a pore. Spores variously septate. Spore cells cylindrical or cuboid. Spores colourless, elongate or ovate 1-5-septate 2. Arthopyrenia Massal. Spores colourless, filiform 1-multi-septate 3. Leptorhaphis Koerb. Spores colourless, muriform 4. Polyblastropsis A. Zahlbr. Spores brown, ovoid or elongate 2-5-septate 5. Microthelia Koerb. Spore cells globose or lentiform, 3-multi-septate 6. *Pseudopyrenula Müll.-Arg. Paraphyses unbranched free. Spore cells cylindrical or cuboid. Perithecia beset with hairs 7. *Stereochlamys Müll.-Arg. Perithecia naked. Asci disappearing; spores elongate multi-septate, colourless 8. *Belonia Koerb. Asci persistent. Spores simple, ellipsoid, colourless 9. *Coccotrema Müll.-Arg. Spores elongate, 1-multi-septate, colourless 10. Porina Müll.-Arg. Spores elongate, 1-multi-septate, brown 11. Blastodesmia Massal. Spores muriform, colourless 12. *Clathroporina Müll.-Arg. Spores elongate, 2-3-septate, colourless 13. Thelopsis Nyl. Spore cells globose or lentiform. Spores elongate, 1-5-septate, brown 14. Pyrenula Massal. Spores muriform, brown 15. Anthracothecium Massal.
VIII. _PARATHELIACEAE_
This family is peculiar in that the perithecia open by a somewhat elongate ostiole that slants at an oblique angle. The algal cells are _Trentepohlia_. Genera and species are endemic in tropical or subtropical regions of the Western hemisphere, though a species of _Pleurotrema_ has been found in subantarctic America. They are corticolous and the thallus is either superficial or embedded. The genera are arranged according to spore characters:
Spores elongate, 2- or more-septate. Spore cells cylindrical, colourless 1. *Pleurotrema Müll.-Arg. Spore cells globose-lentiform. Spores colourless 2. *Plagiotrema Müll.-Arg. Spores brown 3. *Parathelium Müll.-Arg. Spores muriform. Spores colourless 4. *Campylothelium Müll.-Arg. Spores brown 5. *Pleurothelium Müll.-Arg.
IX. _TRYPETHELIACEAE_
This and the following two families are distinguished by the pseudostroma or compound fruit, a character rare among lichens, though the true stroma is frequent in Pyrenomycetes in such genera as _Dothidea_, _Valsa_, etc. The genera are crustaceous and corticolous and occur with few exceptions in tropical or subtropical regions, mostly in the Western Hemisphere. Several grow on officinal bark (_Cinchona_, etc.). Algal cells are _Trentepohlia_. As in many tropical lichens, the spores are large. The genera are based chiefly on spore characters, on septation, and on the form of the spore cells:
Spore cells cylindrical or cuboid. Spores colourless, elongate, multi-septate 1. *Tomasiella Müll.-Arg. Spores colourless, muriform 2. *Laurera Rehb. Spores brown, muriform 3. *Bottaria Massal. Spore cells globose-lentiform. Spores colourless, elongate, multi-septate 4. *Trypethelium Spreng. Spores brown, elongate, multi-septate 5. Melanotheca Müll.-Arg.
X. _ASTROTHELIACEAE_
The perithecia are either upright or inclined, and occur usually in radiate groups. They are free or united in a stroma, and the elongate ostioles open separately or coalesce in a common canal. The genera are all crustaceous, with _Trentepohlia_ gonidia. They are tropical or subtropical, mostly in the Western Hemisphere; but species of _Parmentaria_ and _Astrothelium_ have been recorded also from Australia.
The spores are all many-celled and the form of their cells is a generic character:
Spores elongate, multi-septate. Spore cells cylindrical 1. *Lithothelium Müll.-Arg. Spore cells globose-lentiform. Spores colourless 2. *Astrothelium Trev. Spores brown 3. *Pyrenastrum Eschw. Spores muriform. Spores colourless 4. *Heufleria Trev. Spores brown 5. *Parmentaria Fée.
XI. _MYCOPORACEAE_
A small family with only two genera which are found in both Hemispheres; species of both occur in Great Britain. They are all corticolous. The perithecia are united into a partially chambered fruiting body surrounded by a common wall, but opening by separate ostioles. The thallus is thinly crustaceous, with _Palmella_ gonidia in _Mycoporum_, and _Trentepohlia_ in _Mycoporellum_. The spores are colourless or brown in both genera:
Spores muriform 1. Mycoporum Flot. Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr.
XII. _PHYLLOPYRENIACEAE_
Thallus foliose with both surfaces corticate and attached by rhizinae. Algal cells _Trentepohlia_. There is but one genus, _Lepolichen_, which has a laciniate somewhat upward growing thallus. Two species, both from South America, have been described, _L. granulatus_ Müll.-Arg. and _L. coccophora_ Hue. The latter has been recently examined by Hue[1041] who finds, on the thalli, cephalodia which are peculiar in containing bright-green gelatinous algae either _Urococcus_ or _Gloeocystis_, one of the few instances known of chlorophyllaceous algae forming part of a cephalodium. _Gloeocystis_ may be the only alga present in the cephalodium; _Urococcus_ is always accompanied by _Scytonema_.
The perithecia are immersed in thalline tubercles:
Spores colourless, simple, ovoid or ovoid-elongate 1. *Lepolichen Trevis.
XIII. _STRIGULACEAE_
A family of epiphyllous lichens inhabiting and disfiguring coriaceous evergreen leaves, or occasionally fern leaves in tropical or subtropical regions. The algae associated are _Mycoidea_ and _Phycopeltis_ (_Phyllactidium_). The only truly parasitic lichen, _Strigula_, belongs to this family: the alga precedes the lichen on the leaves and is gradually invaded by the hyphae of the lichen and altered in character. The small black perithecia are scattered over the surface. In _Strigula_ the lichen retains the spreading rounded form of the alga. The other genera are more irregular.
Thallus orbicular in outline 1. *Strigula Fries. Thallus irregular. Perithecia without hairs. Spores colourless. Spores elongate, multi-septate 2. *Phylloporina Müll.-Arg. Spores muriform 3. *Phyllobathelium Müll.-Arg. Spores brown. Spores simple 4. *Haplopyrenula Müll.-Arg. Spores elongate, 1-3-septate 5. *Microtheliopsis Müll.-Arg. Perithecia beset with stiff hairs 6. *Trichothelium Müll.-Arg.
XIV. _PYRENIDIACEAE_
The only family of Pyrenocarpineae associated with blue-green algae. The genera of Pyrenidiaceae are all monotypic, only one is common and of wide distribution, _Coriscium_ (_Normandina_ Nyl.). _Pyrenidium_ is the only member that has a fruticose thallus, and that is of minute dimensions. _Eolichen Heppii_, found and described by Zukal, is a doubtful lichen. “_Lophothelium_” Stirton is a case of parasitism of a fungus, _Ticothecium_, on the squamules of _Stereocaulon condensatum_.
Algal cells _Scytonema_ or _Stigonema_.
Thallus crustaceous[1042]; spores simple, colourless 1. *Rhabdopsora Müll.-Arg. Thallus crustaceous; spores 1-septate, colourless 2. *Eolichen Zuk. Thallus crustaceous; spores muriform, brown 3. *Pyrenothrix Riddle[1043]. Thallus squamulose; spores numerous, simple 4. *Placothelium Müll.-Arg.
Algal cells _Nostoc_.
Thallus crustaceous; spores filiform, simple, colourless 5. *Hassea A. Zahlbr. Thallus fruticose; spores elongate, 3-septate, brown 6. Pyrenidium Nyl.
Algal cells _Microcystis_ (_Polycoccus_).
Thallus squamulose; fructification unknown 7. Coriscium Wainio.
SERIES II. =GYMNOCARPEAE=
SUBSERIES 1. =Coniocarpineae=
This small subseries is marked by the peculiar “mazaedium” type of fruit with its disappearing asci. It forms a connecting link between the families with perithecia and those with apothecia. The thallus is crustaceous or fruticose, often poorly developed and sometimes absent. The algal cells are Protococcaceae or rarely _Trentepohlia_.
XV. _CALICEACEAE_
The thallus is thinly crustaceous, sometimes brightly coloured, sometimes absent, taking no part in the formation of the fruits; these have upright stalks with a small capitulum, and often look like minute nails. One genus, _Sphinctrina_, is parasitic on the thallus of other lichens, mostly _Pertusariae_.
Fruits with slender stalks. Spores simple. Spores colourless 1. Coniocybe Ach. Spores brown 2. Chaenotheca Th. Fr. Spores septate, brown. Spores 1-septate 3. Calicium De Not. Spores 3-7-septate 4. Stenocybe Nyl. Fruits with short thick stalks. Spores globose, brown (parasitic) 5. Sphinctrina Fries. Spores 1-septate, brown 6. *Pyrgidium Nyl.
XVI. _CYPHELIACEAE_
Thallus crustaceous. Algal cells Protococcaceae or _Trentepohlia_. Apothecia sessile, more widely open than in the previous family; in some genera the thallus forms an outer apothecial margin. The genera _Farriola_ from Norway and _Tylophorella_ from New Granada are monotypic. The British genus _Cyphelium_ has been known as _Trachylia_.
Thallus with Protococcaceae.
Spores colourless, simple 1. *Farriola Norm. Spores brown, 1-3-septate (rarely simple or muriform) 2. Cyphelium Th. Fr.
Thallus with _Trentepohlia_.
Spores simple, many in the ascus 3. *Tylophorella Wainio. Spores 8 in the ascus. Apothecia with a thalline margin 4. *Tylophoron Nyl. Apothecia without a thalline margin 5. *Pyrgillus Nyl.
XVII. _SPHAEROPHORACEAE_
The most highly evolved family of the subseries, as regards the thallus. Algal cells Protococcaceae. In _Tholurna_, a small lichen endemic in Scandinavia, there is a double thallus: one of horizontal much-divided squamules, the other swollen, upright, terminating in the capitulum. The fruit is lateral in _Calycidium_, a squamulose form from New Zealand, and in _Pleurocybe_ from Madagascar, with stiff strap-shaped fronds. All the genera are monotypic except _Sphaerophorus_, of which genus ten species are recorded, some of them with a world-wide distribution. The spores are brown and simple or 1-septate.
Thallus squamulose and upright 1. *Tholurna Norm. Thallus wholly squamulose 2. *Calycidium Stirton. Thallus fruticose. Fronds hollow in the centre 3. *Pleurocybe Müll.-Arg. Fronds not hollow. Fruit without a thalline margin 4. *Acroscyphus Lév. Fruit inclosed in the tip of the fronds 5. Sphaerophorus Pers.
SUBSERIES 2. =Graphidineae=
In this subseries are included five families that differ rather widely from each other both in thallus and apothecia; the latter are more or less carbonaceous and mostly with a proper margin only. Families and genera are widely distributed, though most abundant in warm regions. Algal cells mostly _Trentepohlia_.
A comprehensive study of the apothecia of this series by Bioret[1044] gives some interesting results in regard to the paraphyses: in _Arthonia_ they are irregular in direction and much-branched; in _Opegrapha_, the paraphyses are vertical and parallel with more regular branching; _Stigmatidium_ (_Enterographa_) resembles _Opegrapha_ in this respect as does also _Platygrapha_, a genus of Lecanactidaceae, while in _Graphis_ the paraphyses are vertical, unbranched and free; _Melaspilea_ paraphyses are somewhat similar to those of _Graphis_.
XVIII. _ARTHONIACEAE_
The thallus of Arthoniaceae is corticolous with few exceptions and is very inconspicuous, being largely embedded in the substratum. The apothecia (ardellae) are round, irregular or stellate, without any margin, the hymenium being protected by the dense branching of the paraphyses at the tips.
_Arthonia_ is abundant everywhere. The species of the other genera belong mostly to tropical or subtropical countries. _Arthoniopsis_ is similar to _Arthonia_ in the character of the fruits, but the gonidium is a _Phycopeltis_, and it is only found on leaves. _Synarthonia_ with peculiar stromatoid fructification is monotypic; it occurs in Costa Rica.
Thallus with _Trentepohlia_ gonidia.
Apothecia scattered. Spores elongate 1- or pluri-septate 1. Arthonia Ach. Spores muriform 2. Arthothelium Massal. Apothecia stromatoid. Spores elongate, multi-septate 3. *Synarthonia Müll.-Arg.
Thallus with _Palmella_ gonidia.
Spores 1- or more-septate 4. Allarthonia Nyl. Spores muriform 5. *Allarthothelium Wain.
Thallus with _Phycopeltis_ gonidia.
Spores elongate 1- or more-septate 6. *Arthoniopsis Müll.-Arg.
XIX. _GRAPHIDACEAE_
Thallus crustaceous, inconspicuous, partly immersed, mainly growing on bark but occasionally on dead wood or stone. Algal cells chiefly _Trentepohlia_, very rarely _Palmella_ or _Phycopeltis_ (epiphyllous). Apothecia (lirellae) carbonaceous more or less linear, opening by a narrow slit with a well-developed proper margin except in _Gymnographa_, a monotypic Australian genus. In two genera, the fruit is of a compound nature, several parallel discs occurring in one lirella: these are _Ptychographa_ (on bark in Scotland) and _Diplogramma_ (Australia), both are monotypic. They must not be confused with _Graphis elegans_ and allied species in which the sterile carbonaceous margin is furrowed. Two tropical genera associated with _Phycopeltis_ are epiphyllous.
Graphidaceae are among the oldest recorded lichens, attention having been drawn to them since early times by the resemblance of the lirellae on the bark of trees to hieroglyphic writing.
Thallus with _Palmella_ gonidia.
Apothecia single. Hypothecium dark-brown. Spores simple 1. Lithographa Nyl. Hypothecium colourless or brownish. Spores colourless. Spores simple 2. Xylographa Fries. Spores elongate 3-8-septate 3. *Aulaxina Fée. Spores brown. Spores 1-septate 4. Encephalographa Massal. Spores pluri-septate, then muriform 5. *Xyloschistes Wain. Apothecia compound. Spores simple, colourless 6. Ptychographa Nyl. Spores pluri-septate, colourless 7. *Diplogramma Müll.-Arg.
Thallus with _Trentepohlia_ gonidia.
Spores elongate 1-multi-septate, the cells longer than wide. Spores brown. Spores 1-(rarely more)-septate 8. Melaspilea Nyl. Spores 3-septate (apothecia rudimentary) 9. *Gymnographa Müll.-Arg. Spores colourless. Spores acicular, coiled (many in the ascus) 10. *Spirographa A. Zahlbr. Spores fusiform, straight 11. Opegrapha Humb. Spores muriform. Spores elongate, central cells finally muriform 12. *Dictyographa Müll.-Arg.
Spores elongate, septate, cells wider than long. Paraphyses unbranched, filiform. Spores multi-septate, colourless 13. Graphis Adans. Spores multi-septate, brown 14. Phaeographis Müll.-Arg. Spores muriform, colourless 15. Graphina Müll.-Arg. Spores muriform, brown 16. Phaeographina Müll.-Arg. Paraphyses clavate, warted at tips 17. *Acanthothecium Wain. Paraphyses branched, interwoven above 18. *Helminthocarpon Fée.
Thallus with _Phycopeltis_ gonidia (epiphyllous).
Spores elongate, 3-9-septate, colourless 19. *Opegraphella Müll.-Arg. Spores elongate, 1-septate, brown 20. *Micrographa Müll.-Arg.
XX. _CHIODECTONACEAE_
Specially distinguished in this subseries by the grouping of the somewhat rudimentary apothecia in pseudostromata in which they are almost wholly immersed. In form they are roundish or linear; the spores are septate or muriform. The thallus is thinly crustaceous and continuous: in _Glyphis_, _Sarcographa_ and _Sarcographina_ there is an amorphous upper cortex, the other genera are non-corticate. Algal cells are _Trentepohlia_ with the exception of two epiphyllous genera associated with _Phycopeltis_.
Genera and species are mostly tropical. _Sclerophyton_ with five species is represented in Europe by a single British specimen, _S. circumscriptum_.
The form of the paraphyses is a distinguishing character of the genera.
Thallus with _Trentepohlia_ gonidia.
Paraphyses free, unbranched. Spore cells short or almost globose. Spores elongate, multi-septate, colourless 1. Glyphis Fée. Spores elongate, multi-septate, brown 2. *Sarcographa Fée. Spores muriform, brown 3. *Sarcographina Müll.-Arg. Spore cells longer and cuboid. Spores muriform, colourless 4. *Enterodictyon Müll.-Arg. Paraphyses branched, interwoven above. Spores elongate, multi-septate, colourless 5. Chiodecton Ach. Spores elongate, multi-septate, brown 6. Sclerophyton Eschw. Spores muriform, colourless 7. *Minksia Müll.-Arg. Spores muriform, brown 8. *Enterostigma Müll.-Arg.
Thallus with _Phycopeltis_ gonidia (epiphyllous).
Paraphyses free. Spores unequally 2-celled, colourless 9. *Pycnographa Müll.-Arg. Paraphyses branched, interwoven above. Spores elongate, multi-septate, colourless 10. *Mazosia Massal.
XXI. _DIRINACEAE_
A small family, which is associated with and often included under Graphidaceae. The thallus is crustaceous and corticate on the upper surface, the cortex being formed of palisade hyphae. Algal cells _Trentepohlia_. Apothecia are rounded or with a tendency to elongation, and, in addition to a thin proper margin, possess a stout thalline margin; the hypothecium is thick and carbonaceous. There are two genera: _Dirina_ with twelve species has a wide distribution; _Dirinastrum_ is monotypic and occurs on maritime rocks in Australia. In both the spores are elongate-septate, differing only in colour:
Spores colourless 1. Dirina Fr. Spores brown 2. *Dirinastrum Müll.-Arg.
XXII. _ROCCELLACEAE_
The Roccellaceae differ from the preceding Dirinaceae chiefly in the fruticose thallus which is more or less characteristic of all the genera, though in _Roccellographa_ it expands into foliose dimensions and in _Roccellina_ is reduced to short podetia-like processes from a crustose base. The fronds—mostly long and strap-shaped—are protected in most of the genera by a cortex of compact palisade hyphae; in a few the outer hyphae are parallel with the long axis. The medulla is of parallel hyphae, either loose or compact. The algal cells are _Trentepohlia_.
The apothecia are lateral except in _Roccellina_ where they occur at the tips of the short upright fronds, and only in _Roccellaria_ is there no thalline margin. They are superficial in all of the genera except _Roccellographa_, in which they are immersed and almost closed, recalling the perithecia-like fruits of _Chiodecton_ (sect. _Enterographa_). The spores are elongate, narrow, pluri-septate, and colourless or brownish, except in _Darbishirella_ in which they are ovoid, 2-septate and brown.
The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first indicated by Reinke[1045] and elaborated later by Darbishire[1046] in his monograph of Roccellaceae. The apothecia in some species of _Dirina_ are ellipsoid rather than round; in several genera of Roccellaceae they are distinctly lirellate, and in _Roccella_ itself some species have ellipsoid fruits. The fruticose thallus is predominant in Roccellaceae, but its evolution from the crustaceous type may be traced through _Roccellina_ which is partly crustaceous and only imperfectly fruticose.
In most of the genera only one species is recorded. _Roccella_, represented by twelve species, is well known for its dyeing properties, and has a wide distribution. Like other Graphidineae they are mainly plants of warm regions, many of them exclusively maritime rock-dwellers.
The following synopsis of the genera is the one given by Darbishire in his monograph.
Cortex fastigate, of palisade hyphae. Spores colourless. Hypothecium black-carbonaceous. Apothecia round. Thallus fruticose 1. Roccella DC. Thallus crustaceous-fruticose 2. *Roccellina Darbish. Apothecia lirellate 3. *Reinkella Darbish. Hypothecium colourless. Gonidia present under the hypothecium 4. *Pentagenella Darbish. Gonidia absent from hypothecium 5. *Combea De Not. Spores brown or brownish. Medulla of parallel somewhat loose hyphae 6. *Schizopelte Th. Fr. Medulla solid, black 7. *Simonyella Steiner. Cortex fibrous, of parallel hyphae. Apothecia round. Hypothecium black-carbonaceous. Apothecia with thalline margin 8. *Dendrographa Darbish. Apothecia with proper margin 9. *Roccellaria Darbish. Hypothecium colourless 10. *Darbishirella A. Zahlbr. Apothecia lirellate 11. *Ingaderia Darbish.
SUBSERIES 3. =Cyclocarpineae=
This last subseries includes the remaining twenty-nine families of Ascolichens. They are very varied both in the fungal and the algal symbionts. The fruit is more or less a discoid open apothecium. The gonidia belong to different genera of Myxophyceae and Chlorophyceae, but the most frequent are Protococcaceae. Families are based largely on thalline structure.
XXIII. _LECANACTIDACEAE_
By many systematists this family is included under Graphidineae on account of the fruit structure which in some of the forms is carbonaceous and almost lirellate, and also because the algal symbiont is _Trentepohlia_. The thallus is primitive, being thinly crustaceous and non-corticate; the apothecium has a black carbonaceous hypothecium in two of the genera, _Lecanactis_ and _Schismatomma_ (_Platygrapha_); in the third genus, _Melampydium_, it is colourless. The latter is monotypic, and the spores become muriform. In the other genera they are elongate and multi-septate.
Apothecia with prominent proper margin 1. Lecanactis Eschw. Apothecia with thin proper margin 2. *Melampydium Müll.-Arg. Apothecia with thalline margin 3. Schismatomma Flot.
XXIV. _PILOCARPACEAE_
A small family with but one genus, _Pilocarpon_. It is distinguished as one of the few epiphyllous genera of lichens associated with Protococcaceous gonidia and with a distribution extending far beyond the tropics. The best known species, _P. leucoblepharum_, encircles the base of pine-needles with a white felted crust, or inhabits coriaceous evergreen leaves. Another species lives on fern leaves. The fruit is a discoid apothecium with a dark carbonaceous hypothecium and proper margin, and with a second thalline margin. The paraphyses are branched and interwoven above.
Spores elongate, 3-septate, colourless 1. Pilocarpon Wain.
XXV. _CHRYSOTRICHACEAE_
This family now, according to Hue[1047], includes two genera, _Crocynia_ and _Chrysothrix_. In both there is a thallus of interlaced hyphae with Protococcaceous algae scattered through it or in groups. The structure is thus homoiomerous, and Hue has suggested for it a new series, “Intertextae.” The only British species, _Crocynia lanuginosa_, first placed by Nylander[1048] in _Amphiloma_ and later transferred by him to _Leproloma_[1049], has a soft crustaceous lobate thallus, furfuraceous on the surface; no fructification has been found. A West Indian species, _C. gossypina_, has discoid apothecia with a thalline margin. There is only one species of _Chrysothrix_, _Ch. nolitangere_, which forms small clumps or tufts on the spines of Cactus in Chili. The structure is somewhat similar to that of _Crocynia_.
Spores colourless, simple 1. Crocynia Nyl. Spores colourless, 2-3-septate 2. *Chrysothrix Mont.
XXVI. _THELOTREMACEAE_
A tropical or subtropical family of which the leading characteristic is the deeply sunk disc of the apothecium: it has a proper hyphal margin, and, round that, an overarching thalline margin. The apothecia occur singly, or they are united in a kind of pseudostroma: in _Tremotylium_ several grow together, while in _Polystroma_ each new apothecium develops as an outgrowth from the thalline margin of the one already formed, so that an upright, branching succession of fruits is built up. It is a very unusual type of lichen fructification, with one species, _P. Ferdinandezii_, found in Spain and in Guiana.
The thallus in all the genera is crustaceous with an amorphous (decomposed) cortex; or it is non-corticate. The algal cells are _Trentepohlia_ except in _Phyllophthalmaria_, an epiphyllous genus associated with the alga _Phycopeltis_. In _Polystroma_ the alga is unknown.
Only one genus is represented in the British Isles.
Apothecia growing singly. Thallus with _Trentepohlia_ gonidia. Paraphyses numerous, unbranched, free. Spores colourless. Spores elongate, 2- or multi-septate 1. *Ocellularia Spreng. Spores muriform 2. Thelotrema Ach. Spores brown. Spores elongate, septate 3. *Phaeotrema Müll.-Arg. Spores muriform 4. *Leptotrema Mont. Paraphyses scanty, branched. Spores muriform, brown 5. *Gyrostomum Fr. Thallus with _Phycopeltis_ gonidia 6. *Phyllophthalmaria A. Zahlbr. Apothecia in pseudostromata. Apothecia united in tubercles 7. *Tremotylium Nyl. Apothecia united by the margins 8. *Polystroma Clem.
XXVII. _DIPLOSCHISTACEAE_
Scarcely differing from the preceding family except in the gonidia which are Protococcaceous algae. The thallus is crustaceous and non-corticate. The apothecia have a double margin but the outer thalline margin is less overarching than in Thelotremaceae. The spores in the two genera are somewhat peculiar: in _Conotrema_ they are exceedingly long and divided by parallel septa into thirty to forty small cells; in _Diploschistes_ (_Urceolaria_) they are large, muriform and brown. _Conotrema_ contains two corticolous species; _Diploschistes_ about thirty species mostly saxicolous. Both genera are represented in the British Isles.
Spores elongate, multi-septate, colourless 1. Conotrema Tuck. Spores muriform, brown 2. Diploschistes Norm.
XXVIII. _ECTOLECHIACEAE_
A family of tropical epiphyllous lichens that are associated with Protococcaceous gonidia. The thallus is primitive in character, mostly a weft of hyphae with intermingled algal cells, described as homoiomerous.
The apothecia are without a thalline margin, and with a scarcely developed proper margin: their affinity is with the Lecideaceae, though in two genera, _Lecaniella_ and _Arthotheliopsis_, there are gonidia below the hypothecium, a character of Lecanoraceae. The genera are nearly all monotypic; in _Sporopodium_ has been included _Lecidea phyllocharis_ Wainio (Sect. _Gonothecium_), which is distinguished by hymenial gonidia.
Apothecia at first covered by a “veil.” Spores elongate, colourless, septate 1. *Asterothyrium Müll.-Arg. Apothecia uncovered from the first. Gonidia not present below the hypothecium. Paraphyses unbranched, free. Spores muriform 2. *Lopadiopsis Wain. Paraphyses branched. Spores 1-septate 3. *Actinoplaca Müll.-Arg. Spores elongate, multi-septate 4. *Tapellaria Müll.-Arg. Spores muriform 5. *Sporopodium Mont. Gonidia present below the hypothecium. Spores elongate, 2-septate 6. *Lecaniella Wain. Spores muriform 7. *Arthotheliopsis Wain.
XXIX. _GYALECTACEAE_
The algal cells in this family are filamentous; either Myxophyceae (_Scytonema_) or Chlorophyceae (_Trentepohlia_ or _Phyllactidium_). The thallus is crustaceous, and in some cases homoiomerous, as in _Petractis_, where the alga, _Scytonema_, penetrates the substratum as deeply as the hyphae. _Monophiale_, a tropical genus, possesses two kinds of gonidia: the species that grow on bark or mosses are associated with _Trentepohlia_; others that have invaded the surface of leathery evergreen leaves resemble most epiphyllous lichens in being associated with the leaf alga _Phyllactidium_ (_Phycopeltis_). Some species of _Trentepohlia_ exhale when moist an odour of violets. This scent is retained in at least one genus, _Jonaspis_.
The apothecia are superficial, and are soft, waxy and bright-coloured, with prominent margins which are however entirely hyphal: the affinity is therefore with Lecideaceae. In one genus, _Sagiolechia_, the fruit is carbonaceous and dark coloured. The spores of all the genera are colourless.
Apothecia waxy, bright-coloured. Thallus with _Scytonema_ gonidia. Spores elongate, 3-septate 1. Petractis Fr. Thallus with _Trentepholia_ gonidia. Asci 6-8-spored. Spores simple 2. Jonaspis Th. Fr. Spores 1-septate 3. *Microphiale A. Zahlbr. Spores septate or muriform 4. Gyalecta Ach. Asci 12-many-spored. Spores 1-septate 5. *Ramonia Stizenb. Spores fusiform or acicular, many-septate 6. Pachyphiale Lönnr. Apothecia carbonaceous. Spores elongate, 2-3-septate 7. *Sagiolechia Massal.
XXX. _COENOGONIACEAE_
There are only two genera in this small family, _Coenogonium_ with _Trentepohlia_ gonidia, and _Racodium_ with _Cladophora_. Both genera follow the algal form and are filamentous. In _Coenogonium_ the filaments are sometimes matted into a loose felted expansion. The genus is mainly tropical or subtropical and mostly rather light-coloured. There is only one British species, _C. ebeneum_[1050], a sterile form, in which the hyphae are very dark-brown; it often covers large areas of stone or rock with its sooty-like creeping filaments.
_Racodium_ includes 2 (?) species. One of these, _R. rupestre_, is sterile and resembles _C. ebeneum_ in form and colour.
The apothecia of _Coenogonium_ are waxy and light-coloured; they are borne laterally on the filaments; the spores are simple or 1-septate.
Thallus with _Trentepohlia_ gonidia 1. Coenogonium Ehrenb. Thallus with _Cladophora_ gonidia 2. Racodium Fr.
XXXI. _LECIDEACEAE_
One of the largest lichen families as regards both genera and species, and of world-wide distribution. The algal cells are Protococcaceae. The thallus is mostly crustaceous but it becomes squamulose in _Psora_, a section of _Lecidea_; and in _Sphaerophoropsis_, a Brazilian genus, there are small upright fronds or stalks with lateral apothecia. The prevailing colour of the thallus is some shade of grey, but it ranges from white or yellow to dark-brown or almost black. Cephalodia appear in some of the species.
The apothecia have a proper margin only, no gonidia taking part in the fruit-formation. They may be soft and waxy (biatorine) or hard and carbonaceous (lecideine). The genera are mainly based on spore characters which are very varied.
The arrangement of genera given below follows that of Zahlbruckner; in several instances, both as to the limitations of genera and to the nomenclature, it differs from that of British text-books, though the general principle of classification is the same.
Thallus crustaceous non-corticate. Spores simple. Spores small, thin-walled. Spores colourless 1. Lecidea Ach. Spores brown 2. *Orphniospora Koerb. Spores large, thick-walled 3. Mycoblastus Norm. Spores 1-septate. Spores small, thin-walled 4. Catillaria Th. Fr. Spores large, thick-walled 5. Megalospora Mey. and Flot. Spores elongate, 3-multi-septate. Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr. Spores elongate, large and thick-walled 7. Bombyliospora De Not. Spores muriform. Spores colourless; on trees 8. Lopadium Koerb. Spores colourless to brown; on rocks 9. Rhizocarpon Th. Kr. Thallus warted or squamulose, corticate. Spores elongate, 1-7-septate, thin-walled 10. Toninia Th. Fr. Thallus of upright podetia-like small fronds. Spores ellipsoid, becoming 1-septate 11. *Sphaerophoropsis Wain.
XXXII. _PHYLLOPSORACEAE_
A small family of exotic lichens with a somewhat more developed thallus than that of the Lecideaceae, being in both of the genera squamulose or almost foliose.
The apothecia are without a thalline margin; they are biatorine or lecideine; the hypothecium is formed of plectenchyma and is purple-red in one species, _Phyllopsora furfuracca_. The two genera differ only in spore characters. There are fifteen species, mostly corticolous, belonging to _Phyllopsora_; only one, from New Zealand, is recorded for _Psorella_.
Spores simple 1. *Phyllopsora Müll.-Arg. Spores elongate, septate 2. *Psorella Müll.-Arg.
XXXIII. _CLADONIACEAE_
Associated with Lecideaceae in the type of apothecium, but differing widely in thallus formation. The latter is of a twofold type: the primary thallus is crustaceous, squamulose, or very rarely foliose; the secondary thallus or podetium, upright, simple or branched, is terminated by the apothecia, or broadens upwards to cup-like scyphi. Algal cells, Protococcaceae, according to Chodat, _Cystococcus_.
Much attention has been given to the origin and development of the podetia in this family. They are superficial on granule or squamule except in the monotypic Himalayan genus _Gymnoderma_ where they are marginal on the large leaf-like lobes. Though in origin the podetia are doubtless fruit stalks, they have become in most cases vegetative in function.
The fruits are coloured yellowish, brown or red (or dark and carbonaceous in _Pilophorus_), and are borne on the tips of the branches or on the margins of the scyphi. In _Glossodium_ and _Thysanothecium_—the former from New Granada, the latter from Australia—the apothecia occupy one side of the widened surface at the tips.
Cephalodia are developed on the primary thallus of _Pilophorus_, and on the podetia of _Stereocaulon_ and _Argopsis_.
Podetia simple, short, not widening upwards. Podetial stalks naked. Primary thallus thin, continuous 1. Gomphillus Nyl. Primary thallus granular or squamulose 2. Baeomyces Pers. Primary thallus foliose. Podetia superficial 3. *Heteromyces Müll.-Arg. Podetia marginal 4. *Gymnoderma[1051] Nyl. Podetial stalks granular, squamulose 5. Pilophorus Th. Fr. Podetia short, widening upwards. Podetia simple above, rarely divided 6. *Glossodium Nyl. Podetia lobed, leaf-like 7. *Thysanothecium Berk. & Mont. Podetia elongate, variously branched, or scyphous and hollow 8. Cladonia Hill. Podetia elongate, not scyphous, the stalks solid. Spores elongate, septate 9. Stereocaulon Schreb. Spores muriform 10. *Argopsis Th. Fr.
XXXIV. _GYROPHORACEAE_
A small family of foliose lichens allied to Lecideaceae by the character of the fruit—a superficial apothecium in the formation of which the gonidia take no share. There are only three genera, distinguished by differences in spore and other characters. _Dermatiscum_ has light-coloured thallus and fruits; of the two species, one occurs in Central Europe, the other in North America. _Umbilicaria_ and _Gyrophora_ are British; they are dark-coloured rock-lichens and are extremely abundant in Northern regions where they are known as “tripe de roche.” Algal cells Protococcaceae.
_Umbilicaria_, _Dermatiscum_, and some species of _Gyrophora_ are attached to the substratum by a central point. Other species of _Gyrophora_ are rhizinose. In all there is a cortex of plectenchyma above and below. In _Gyrophora_ the thallus may be monophyllous as in _Umbilicaria_, or polyphyllous and with or without rhizinae. New lobes frequently arise from protuberances or warts on the older parts of the thallus. At the periphery, in most species, growth is equal along the margins, in _G. erosa_[1052] the edge is formed of numerous anastomosing lobes with lateral branching, the whole forming a broadly meshed open network. Further back the tissues become continuous owing to the active growth of the lower tissue or hypothallus, which grows out from all sides and meets across the opening. The overlying layers, with gonidia, follow more slowly, but they also in time become continuous, so that the “erose” character persists only near the periphery. This forward growth of the lower thallus occurs in other species, though to a much less marked degree.
There is abundant detritus formation in this family; the outer layers of the cortex are continually being sloughed, the dead tissues lying on the upper surface as a dark gelatinous layer, continuous or in small patches. On the under surface the cast-off cortex gathers into a loose confused mass of dead tissues.
Asci 8-spored. Spores mostly simple (disc gyrose) 1. Gyrophora Ach. Spores 1-septate 2. *Dermatiscum Nyl. Asci 1-2-spored. Spores muriform 3. Umbilicaria Hoffm.
XXXV. _ACAROSPORACEAE_
Thallus foliose, squamulose or crustaceous, sometimes scarcely developed. Algal cells Protococcaceae.
Into this family Zahlbruckner has gathered the genera in which the asci are many-spored, as he considers that a character of great importance in determining relationship, but he has in doing so overlooked other very great differences. The fruit-bodies are round and completely enclosed in a thalline wall in _Thelocarpon_, which has however no perithecial wall. They have a proper margin only (lecideine) in _Biatorella_, and a thalline margin (lecanorine) in the remaining genera. In _Acarospora_ the apothecia are sunk in the thallus. Stirton’s genus _Cryptothecia_[1053] is allied to _Thelocarpon_ in the fruit-formation, but the basal thallus is well developed and the spores are few in number and variously divided.
Thallus none. Apothecia (or perithecia) in thalline warts 1. Thelocarpon Nyl. Thallus crustaceous. Apothecia lecideine; spores simple 2. Biatorella Th. Fr. Apothecia lecanorine; spores septate 3. *Maronea Massal. Thallus of small squamules 4. Acarospora Massal. Thallus almost foliose, attached centrally 5. *Glypholecia Nyl.
XXXVI. _EPHEBACEAE_
A family of very simple structure either filamentous, foliose or crustaceous. The algal cells which give a dark colour to the thallus are _Stigonema_ or _Scytonema_, members of the blue-green Myxophyceae, and consist of minute simple or branched filaments—single cell-rows in _Scytonema_, compound in _Stigonema_.
In some of the genera the lichen hyphae travel within the gelatinous sheath of the filaments, both algae and hyphae increasing by apical growth so that filaments many times the length of the alga are formed as in _Ephebe_. In others the filaments scarcely increase beyond the normal size of the alga as in _Thermutis (Gonionema)_; or the gelatinous algal cells may be distributed in a stratum of hyphae.
The apothecia are minute and almost closed; they may be embedded in swellings of the thallus, or are more or less superficial. The spores are rather small, colourless and simple or 1-septate.
The lichens of this family are rock-dwellers and are mostly to be found in hilly or Alpine regions. A tropical species, _Leptogidium dendriscum_, occurs in sterile condition in south-west Ireland. There are few species in any of the genera.
Algal cells _Scytonema_. Thallus minutely fruticose, non-corticate 1. Thermutis Fr. Thallus minute, of felted filaments, cortex one cell thick 2. *Leptodendriscum Wain. Thallus of elongate filaments, cortex of several cells 3. Leptogidium Nyl. Thallus foliose or fruticose, cellular throughout 4. Polychidium Ach. Thallus crustaceous, non-corticate 5. Porocyphus Koerb. Algal cells _Stigonema_. Thallus minutely fruticose, non-corticate 6. Spilonema Born. Thallus of long branching filaments. Spores septate; paraphyses wanting 7. Ephebe Fr. Spores simple; paraphyses present 8. Ephebeia Nyl. Thallus crustaceous; upper surface non-corticate, lower surface corticate 9. *Pterygiopsis Wain.
XXXVII. _PYRENOPSIDACEAE_
In this family are included gelatinous lichens of which the gonidium is a blue-green alga with a thick gelatinous coat, either _Gloeocapsa_ (including _Xanthocapsa_) or _Chroococcus_. In _Gloeocapsa_ and _Chroococcus_ the gelatinous envelope is often red, in _Xanthocapsa_ it is yellow, and these colours persist more or less in the lichens, especially in the outer layers.
The thallus is in many cases a formless gelatinous crust of hyphal filaments mingling with colonies of algal cells as in _Pyrenopsis_; but small fruticose tufts are characteristic of _Synalissa_, and larger foliose and fruticose thalli appear in some exotic genera. A plectenchymatous cortex is formed on the thallus of _Forssellia_, a crustaceous genus from Central Europe, with two species only; the whole thallus is built up of a kind of plectenchyma in some others, but in most of the genera there is no tissue formed.
The apothecia, as in Ephebaceae, are generally half-closed.
Thallus with _Gloeocapsa_ gonidia. Thallus crustaceous. Spores simple 1. Pyrenopsis Nyl. Spores 1-septate 2. *Cryptothele Forss. Thallus shortly fruticose 3. Synalissa Fr. Thallus lobate, centrally attached 4. *Phylliscidium Forss. Thallus with _Chroococcus_ gonidia. Thallus crustaceous 5. Pyrenopsidium Forss. Thallus lobate, centrally attached 6. *Phylliscum Nyl. Thallus with _Xanthocapsa_ gonidia. Thallus crustaceous. Thallus non-corticate. Spores simple. Apothecia open, asci 8-spored 7. Psorotichia Forss. Apothecia covered, asci many-spored 8. *Gonohymenia Stein. Spores 1-septate. Apothecia closed 9. *Collemopsidium Nyl. Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr. Thallus lobate, centrally attached. Spores simple. Thallus plectenchymatous throughout 11. *Anema Nyl. Thalline tissue of loose hyphae 12. *Thyrea Massal. Cortex of upright parallel hyphae 13. *Jenmania Wächt. Spores 1-septate. Thalline tissue of loose hyphae 14. *Paulia Fée. Thallus fruticose. Thallus without a cortex 15. *Peccania Forss. Thallus with cortex of parallel hyphae 16. *Phloeopeccania Stein.
XXXVIII. _LICHINACEAE_
The only family of lichens associated with _Rivularia_ gonidia, the trichomes of which retain their filamentous form to some extent in the more highly developed genera; they lie parallel to the long axis of the squamule or of the frond except in _Lichinella_ in which genus they are vertical to the surface. The thallus may be crustaceous, or minutely foliose, or fruticose; in all cases it is dark-brown in colour, and the gelatinous character is evident in the moist condition. The best known British genus is _Lichina_ which grows on rocks by the sea.
The apothecia are more or less immersed in the tissue; in _Pterygium_ and _Steinera_ they are open and superficial (the latter monotypic genus confined to Kerguelen). They are also open in _Lichinella_ and _Homopsella_, both very rare genera. The spores are colourless and simple except in _Pterygium_ and _Steinera_ where they are elongate, and 1-3-septate.
Thallus crustaceous squamulose. Apothecia immersed in thalline warts 1. *Calothricopsis Wain. Apothecia superficial, with thalline margin 2. *Steinera A. Zahlbr. Apothecia superficial, without a thalline margin 3. Pterygium Nyl. Thallus of small fruticose fronds. Gonidia occupying the central strand 4. *Lichinodium Nyl. Gonidia not in the centre. Apothecia immersed 5. Lichina Ag. Apothecia superficial. Paraphyses present 6. *Lichinella Nyl. Paraphyses absent 7. *Homopsella Nyl.
XXXIX. _COLLEMACEAE_
The most important family of the gelatinous lichens and the most numerous. _Collema_ is historically interesting as having first suggested the composite thallus. Algal cells, _Nostoc_, which retain the chain-like form except in _Leprocollema_, a doubtful member of the family. The thallus varies from indeterminate crusts to lobes of considerable size; occasionally the lobes are narrow and erect, forming minute fruticose structures. In the more primitive genera the thallus is non-corticate, but in the more evolved, the apical cells of the hyphae coalesce to form a continuous cellular cortex, one or more cells thick, well marked in some species, in others rudimentary; the formation of plectenchyma also occurs occasionally in the apothecial tissues of some non-corticate species.
The apothecia are superficial except in _Pyrenocollema_, a monotypic genus of unknown locality. They are generally lecanorine, with gonidia entering into the formation of the apothecium: in some genera they are lecideine or biatorine, being formed of hyphae alone. The spores are colourless and vary in form, size and septation.
Apothecia immersed; spores fusiform, 1-septate 1. *Pyrenocollema Reinke. Apothecia superficial. Thallus without a cortex. Spores simple, globose or ellipsoid. Thallus crustaceous 2. *Leprocollema Wain. Thallus largely squamulose-fruticose. Apothecia lecideine (dark-coloured) 3. *Leciophysma Th. Fr. Apothecia lecanorine 4. Physma Massal. Spores variously septate or muriform. Apothecia biatorine (light-coloured) 5. *Homothecium Mont. Apothecia lecanorine 6. Collema Wigg. Thallus with cortex of plectenchyma. Spores simple. Spores globose 7. Lemmopsis A. Zahlbr. Spores ellipsoid, with thick subverrucose wall 8. *Dichodium Nyl. Spores vermiform, spirally curved 9. *Koerberia Massal. Spores variously septate or muriform. Apothecia biatorine (light-coloured) 10. *Arctomia Th. Fr. Apothecia lecanorine 11. Leptogium S. F. Gray.
XL. _HEPPIACEAE_
A family belonging to the “blue-green” series as it is associated with a gelatinous alga, _Scytonema_, but is of almost entirely cellular structure and is non-gelatinous. The thallus is squamulose or minutely foliose, or is formed of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci are 4-many-spored.
_Heppia_ is a wide-spread genus both in northern and tropical regions with about forty species that live on soil or rock. So far, no representative has been recorded in our Islands.
Spores simple, colourless, globose or ellipsoid 1. *Heppia Naeg. Spores muriform, colourless, ellipsoid 2. *Amphidium[1054] Nyl.
XLI. _PANNARIACEAE_
The members of this family are also non-gelatinous, though for the most part associated with blue-green gelatinous algae, _Nostoc_ or _Scytonema_. The gonidia are bright-green in the genera _Psoroma_ and _Psoromaria_, the former often included under _Lecanora_, but too closely resembling _Pannaria_ to be dissociated from that genus.
The thallus varies from being crustaceous to squamulose or foliose, and has a cortex of plectenchyma on the upper and sometimes also on the lower surface. The apothecia are superficial or lateral and with or without a thalline margin (lecanorine or biatorine), the spores are colourless.
Zahlbruckner has included _Hydrothyria_ in this family. It is a monotypic aquatic genus found in North America and very closely allied to _Peltigera_. The British species of the genus, familiarly known as _Coccocarpia_, have been placed under _Parmeliella_, the former name being restricted to the tropical or subtropical species first assigned to _Coccocarpia_ and distinguished by the cortex, the hyphae forming it lying parallel with the surface though forming a regular plectenchyma.
An Antarctic lichen _Thelidea corrugata_ with _Palmella_ gonidia is doubtfully included: the thallus is foliose, the apothecia biatorine with colourless 1-septate spores.
Thallus with bright-green gonidia. With _Palmella_ 1. *Thelidea Hue. With Protococcaceae. Apothecia non-marginate (biatorine) 2. *Psoromaria Nyl. Apothecia marginate 3. Psoroma Nyl. Thallus with _Scytonema_ gonidia. Apothecia marginate, spores 1-septate 4. Massalongia Koerb. Apothecia non-marginate; spores simple. Upper surface smooth 5. *Coccocarpia Pers. Upper surface felted 6. *Erioderma Fée. Thallus with _Nostoc_ gonidia. Apothecia marginate; spores simple 7. Pannaria Del. Apothecia non-marginate; spores various. Thallus crustaceous or minutely squamulose 8. Placynthium Ach. Thallus squamulose, cortex indistinct 9. *Lepidocollema Wain. Thallus squamulose or foliose, cortex cellular 10. Parmeliella Müll.-Arg. Thallus foliose, thin veined below 11. *Hydrothyria Russ.
XLII. _STICTACEAE_
Thallus foliose, mostly horizontal, with a plectenchymatous cortex on both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae on the lower surface. Algal cells Protococcaceae or _Nostoc_. Cephalodia and cyphellae or pseudocyphellae often present. Apothecia superficial or lateral; spores colourless or brown, variously septate.
The highly organized cortex and the presence of aeration organs—cyphellae or pseudocyphellae—which are almost solely confined to the genus _Sticta_ give this family a high position as regards vegetative development. The two genera are of wide distribution, but _Sticta_ is more abundant in the Southern Hemisphere. _Lobaria pulmonaria_ is one of our largest lichens.
Under surface dotted with cyphellae or pseudocyphellae 1. Sticta Schreb. Under surface without these organs 2. Lobaria Schreb.
XLIII. _PELTIGERACEAE_
A family of heteromerous foliose lichens containing in some instances blue-green (_Nostoc_), in others bright-green (Protococcaceae) gonidia, and thus representing a transition between these two series. They have large or small lobes and grow on the ground or on trees.
Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur in the family and further exemplify the capacity of the fungus hyphae to combine with different types of algae.
The upper surface is a wide cortex of plectenchyma, which in some forms (_Nephromium_) is continued below. In the non-corticate under surface of _Peltigera_, the lower hyphae grow out in hairs or rhizinae, very frequently brown in colour. Intercalary growth of the upper tissues stretches the thallus and tears apart the lower under surface so that the hair-bearing areas become a network of veins, with the white exposed medulla between. In _Peltigera canina_ there is further growth and branching of the hyphae in the veins, adding to the bulk of the interlacing ridges.
From all other foliose lichens Peltigeraceae are distinguished by the flat wholly appressed or peltate apothecia without a thalline margin which arise mostly on the upper surface, but in _Nephromium_ on the extreme margin of the under surface, the tip of the fertile lobe in that case is turned back as the apothecium matures, so that the fruit eventually faces the light. In _Nephroma_ has been included _Eunephroma_ with bright-green gonidia and _Nephromium_ with blue-green.
Bitter[1055] has recorded the finding of apothecia on the under surface of _Peltigera malacea_ and not at the margin, as in _Nephromium_. The plant was otherwise normal and healthy. _Solorinella_, from Central Europe and _Asteristion_ from Ceylon are monotypic genera with poorly developed thalli.
Thallus poorly developed. Asci 6-8-spored; spores 3-5-septate 1. *Asteristion Leight. Asci many-spored; spores 1-septate 2. *Solorinella Anzi. Thallus generally well developed. Apothecia superficial, sunk in the thallus 3. Solorina Ach. Apothecia terminal on upper surface of lobes 4. Peltigera Willd. Apothecia terminal on lower surface of lobes 5. Nephroma Ach.
XLIV. _PERTUSARIACEAE_
Thallus crustaceous, often rather thick and with an amorphous cortex on the upper surface. Algal cells Protococcaceae. Apothecia solitary or several immersed in thalline warts, generally with a narrow opening which barely exposes the disc, and which in one genus, _Perforaria_, is so small as almost to constitute a perithecium; spores are often very large and with thick walls; some if not all are multinucleate and germinate at many points.
In the form of the fruit, this family stands between Pyrenocarpeae and Gymnocarpeae, though more akin to the latter. _Perforaria_, with two species, belongs to New Zealand and Japan. _Pertusaria_ has a world-wide distribution, and _Varicellaria_, a monotypic genus, with a very large two-celled spore, is an Alpine plant, recorded from Europe and from Antarctic America.
Spores simple. Apothecia with pore-like opening 1. *Perforaria Müll.-Arg. Apothecia with a wider opening 2. Pertusaria DC. Spores 1-septate 3. Varicellaria Nyl.
XLV. _LECANORACEAE_
Thallus mostly crustaceous, occasionally squamulose or very rarely minutely fruticulose. The squamulose thallus is corticate above, the under surface appressed and attached to the substratum by penetrating hyphae, often effigurate at the circumference. Algal cells Protococcaceae. Apothecia well distinguished by the thalline margin; spores colourless, simple or variously septate or muriform.
_Lecanora_, _Ochrolechia_, _Lecania_, _Haematomma_ and _Phlyctis_ are cosmopolitan genera, some of them with a very large number of species; the other genera are more restricted in distribution and generally with few species.
The genus _Candelariella_ is of uncertain position; the spores are 8 or many in the ascus and are simple or 1-septate, and not unfrequently become polarilocular as in Caloplacaceae, but there is no parietin present.
Algae distributed through the thallus. Spores simple 1. *Harpidium Koerb. Algae restricted to a definite zone. Spores simple. Thallus grey, white or yellowish. Spores rather small 2. Lecanora Ach. Spores large 3. Ochrolechia Massal. Thallus bright yellow. Spores simple or 1-septate 4. Candelariella Müll.-Arg. Spores 1-septate (rarely pluri-septate). Paraphyses free. Thallus squamulose, effigurate 5. Placolecania Zahlbr. Thallus crustaceous. Apothecial disc brownish 6. Lecania Zahlbr. Apothecial disc flesh-coloured 7. Icmadophila Trevis. Paraphyses branched, intricate 8. *Calenia Müll.-Arg. Spores elongate, pluri-septate. Apothecia superficial 9. Haematomma Massal. Apothecia immersed. Paraphyses free 10. *Phlyctella Müll.-Arg. Paraphyses branched, intricate 11. *Phlyctidia Müll.-Arg. Spores muriform. Apothecia superficial 12. *Myxodictyon Massal. Apothecia immersed 13. Phlyctis Wallr.
XLVI. PARMELIACEAE
A very familiar family of foliose lichens. Genera and species are dorsiventral and stratose in structure, though some _Cetrariae_ are fruticose in habit. Algal cells are Protococcaceae; in _Physcidia_ they are _Palmellae_. In every case the upper surface of the thallus is corticate and generally of plectenchyma, the lower being somewhat similar, but in _Heterodea_ and _Physcidia_, monotypic Australasian genera, the upper cortex is of branching hyphae parallel with the surface, the lower surface being non-corticate.
The _Parmeliae_ are mostly provided with abundant rhizinae; in _Cetrariae_ and _Nephromopsis_ these are very sparingly present, while in _Anzia_ (including _Pannoparmelia_) the medulla passes into a wide net-like structure of anastomosing hyphae.
In _Heterodea_, cyphellae occur on the under surface as in Stictaceae; and in _Cetraria islandica_ bare patches have been described as pseudocyphellae. The latter lichen is one of the few that are of value as human food. Special aeration structures are present on the upper cortex of _Parmelia aspidota_.
Thallus non-corticate below. Apothecia terminal 1. *Heterodea Nyl. Apothecia superficial 2. *Physcidia Tuck. Thallus spongy below 3. *Anzia Stizenb. Thallus corticate below. Asci poly-spored 4. Candelaria Massal. Asci 8-spored. Spermatia acrogenous 5. Parmeliopsis Nyl. Spermatia pleurogenous. Apothecia superficial 6. Parmelia Ach. Apothecia lateral. Apothecia on upper surface 7. Cetraria Ach. Apothecia on lower surface 8. *Nephromopsis Müll.-Arg.
XLVII. _USNEACEAE_
This also is a familiar family of lichens, _Usnea barbata_ the “bearded moss” being one of the first lichens noted and chronicled. Algal cells Protococcaceae. Structure radiate, the upright or pendulous habit characteristic of the family securing all-round illumination. Special adaptations of the cortex or of the internal tissues have been evolved to strengthen the thallus against the strains incidental to their habit of growth as they are attached in nearly all cases by one point only, by a special sheath, or by penetrating hold-fasts.
Apothecia are superficial or marginal and sometimes shortly stalked; spores are simple or variously septate.
_Ramalina_ and _Usnea_, the most numerous, are cosmopolitan genera; _Alectoria_ inhabits northern or hilly regions.
The genus _Evernia_, also cosmopolitan, represents a transition between foliose and fruticose types; the fronds of the two species, though strap-shaped and generally upright, are dorsiventral and stratose, the gonidia for the most part lying beneath one surface; the other (lower) surface is either white or very dark-coloured. _Everniopsis_, formed of thin branching strap-shaped fronds, is also dorsiventral.
A number of genera, _Thamnolia_, _Siphula_, etc. are of podetia-like structure, generally growing in swards. Several of them have been classified with _Cladoniae_, but they lack the double thallus. One of these, _Endocena_, a sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was classified by Hue[1056] along with _Siphula_; recently he has transferred it to his family Polycaulionaceae[1057] based on _Polycauliona regale_ (_Placodium frustulosum_ Darbish.), and allied to _Placodium_ Sect. _Thamnoma_[1058]. In recent studies Hue has laid most stress on thalline characters. He places the new family between “Ramalinaceae” and “Alectoriaceae.” _Dactylina arctica_ is a common Arctic soil-lichen.
Thallus strap-shaped. Structure dorsiventral. Greyish-green above 1. Evernia Ach. Whitish-yellow above 2. *Everniopsis Nyl. Structure radiate alike on both surfaces. Fronds grey; medulla of loose hyphae 3. Ramalina Ach. Fronds yellow; medulla traversed by strands 4. *Letharia A. Zahlbr. Thallus filamentous. Medulla a strong “chondroid” strand 5. Usnea Dill. Medulla of loose hyphae. Spores simple 6. Alectoria Ach. Spores muriform, brown 7. *Oropogon Fr. Thallus of upright podetia-like fronds. Fronds rather long (about two inches), tapering, white 8. Thamnolia Ach. (Cerania S. F. Gray). Fronds shorter, blunt. Medulla solid 9. *Siphula Fr. Medulla partly or entirely hollow. Fronds swollen and tall (about two inches) 10. *Dactylina Nyl. Fronds coralloid, entangled 11. *Endocena Cromb. Fronds short, upright 12. *Dufourea Nyl.
XLVIII. _CALOPLACACEAE_
In this family Zahlbruckner has included the squamulose or crustaceous lichens with colourless polarilocular spores, relegating those with more highly developed thallus or with brown spores to other families. He has also substituted the name _Caloplaca_ for the older _Placodium_, the latter being, as he considers, less well defined.
Algal cells are Protococcaceae. The thallus is mostly light-coloured, generally some shade of yellow, and, with few exceptions, contains parietin, which gives a purple colour on the application of potash. The squamulose forms are closely appressed to the substratum, and have often a definite rounded outline (effigurate). The spores have a thick median septum with a loculus at each end and a connecting canal[1059].
In _Blastenia_ the outer thalline margin is obscure or absent—though gonidia are frequently present below the hymenium. Caloplacaceae occur all over the globe; they are among the most brilliantly coloured of all lichens. _Polycauliona_ Hue[1060] possibly belongs here: though based on thalline rather than on spore characters, one species at least has polarilocular spores.
Apothecia with a distinct thalline margin 1. Caloplaca Th. Fr. Apothecia without a thalline margin 2. Blastenia Th. Fr.
XLIX. _TELOSCHISTACEAE_
Polarilocular colourless spores are the distinguishing feature of this family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus of Teloschistaceae is more highly developed, being either foliose or fruticose, though never attaining to very large dimensions. The cortex of _Xanthoria_ (foliose) is plectenchymatous, that of _Teloschistes_ (fruticose) is fibrous. The species of both genera are yellow or greenish-yellow due to the presence of the lichen-acid parietin.
Both genera have a wide distribution over the globe, more especially in maritime regions.
Thallus foliose 1. Xanthoria Th. Fr. Thallus fruticose 2. Teloschistes Norm.
L. _BUELLIACEAE_
A family of crustaceous lichens distinguished by the brown two-celled spores. Algal cells Protococcaceae. Zahlbruckner has included here _Buellia_ and _Rinodina_; the former with a distinctly lecideine fruit and with thinly septate spores; the latter lecanorine and with spores of the polarilocular type, with a very wide central septum pierced in most of the species by a canal which may or may not traverse the middle lamella of the wall. _Rinodina_ is closely allied to Physciaceae, while _Buellia_ has more affinity with Lecideaceae and is near to _Rhizocarpon_.
Both genera are of world-wide distribution.
Apothecia lecideine, without a thalline margin 1. Buellia De Not. Apothecia lecanorine, with a thalline margin 2. Rinodina Massal.
LI. _PHYSCIACEAE_
Thallus foliose or partly fruticose, and generally attached by rhizinae. Algal cells Protococcaceae. The spores resemble those of _Rinodina_, dark-coloured with a thick septum and reduced cell-lumina. As in that species there may be a second septum in each cell, giving a 3-septate spore; but that is rare.
_Pyxine_, a tropical or subtropical genus, is lecanorine only in the very early stages; it soon loses the thalline margin. _Anaptychia_ is differentiated from _Physcia_ by the subfruticose habit, though the species are nearly all dorsiventral in structure, only a few of them being truly radiate and corticate on both surfaces. The upper cortex of _Anaptychia_ is fibrous, but that character appears also in most species of _Physcia_ either on the upper or the lower side. _Physcia_ and _Anaptychia_ are widely distributed.
Thalline margin absent in apothecia 1. *Pyxine Nyl. Thalline margin present in apothecia. Thallus foliose 2. Physcia Schreb. Thallus fruticose 3. Anaptychia Koerb.
C. *HYMENOLICHENS
Fungus a Basidiomycete, akin to _Thelephora_. Algal cells _Scytonema_ or _Chroococcus_. Thallus crustaceous, squamulose or foliose. Spores colourless, produced on basidia, on the under surface of the free thallus.
The Hymenolichens[1061] are few in number and are endemic in tropical or warm countries. They inhabit soil or trees.
Thallus of extended lobes. Gonidia near the upper surface 1. *Dictyonema Zahlbr. Gonidia in centre of tissue 2. *Cora Fr. Thallus squamulose, irregular 3. *Corella Wain.
II. NUMBER AND DISTRIBUTION OF LICHENS
1. ESTIMATES OF NUMBER
Calculations have been made and published, once and again, as to the number of lichen species occurring over the globe or in definite areas. In 1898 Fünfstück stated that about 20,000 different species had been described, but as many of them had been proved to be synonyms, and since many must rank as forms or varieties, the number of well-authenticated species did not then, according to his estimate, exceed 4000. Many additional genera and species have, however, been discovered since then. In Engler and Prantl’s _Pflanzenfamilien_, over 50 families and nearly 300 genera find a place, but even in these larger groupings opinions differ as to the limits both of genera and families, and lichenologists would not all accept the arrangement given in that volume.
Fünfstück has reckoned that of his estimated 4000, about 1500 are European and of these at least 1200 occur in Germany. Probably this is too low an estimate for that large country. Leighton in 1879 listed, in his _British Lichen Flora_, 1710 in all, and, as the compilation includes varieties, it cannot be considered as very far astray. On comparing it with Olivier’s[1062] recent statistics of lichens, we find that of the larger fruticose and foliose species, 310 are recognized by him for the whole of Europe, 206 of these occurring in the British Isles. Leighton’s estimate of similar species is about 145, without including varieties now reckoned as good species. In a more circumscribed area, Th. Fries[1063] described for Spitzbergen about 210 different lichens, a number that closely approximates to the 206 recent records by Darbishire[1064] for the same area.
A general idea of the comparative numbers of the different types of lichens may be gathered from Hue’s compilation of exotic lichens[1065], examined or described by Nylander, and now in the Paris herbarium. There are 135 genera with 3686 species. Of these, about 829 belong to the larger foliose and fruticose lichens (including _Cladoniae_); the remaining 2857 belong to the smaller kinds, most of them crustaceous.
2. GEOGRAPHICAL DISTRIBUTION
A. GENERAL SURVEY
The larger foliose and fruticose lichens are now fairly well known and described for Europe, and the knowledge of lichens in other continents is gradually increasing. It is the smaller crustaceous forms that baffle the investigator. The distribution of all lichens over the surface of the earth is controlled by two principal factors, climate and substratum; for although lichens as a rule require only support, they are most of them restricted to one or another particular substratum, either organic or inorganic. As organisms which develop slowly, they require an unchanging substratum, and as sun-plants they avoid deeply shaded woodlands: their occurrence thus depends to a large extent on the configuration and general vegetation of the country.
Though so numerous and so widely distributed, lichens have not evolved that great variety of families and genera characteristic of the allied fungi and algae. They conform to a few leading types of structure, and thus the Orders and Families are comparatively few, and more or less universal. They are most of them undoubtedly very old plants and were probably wide-spread before continents and climates had attained their present stability. Arnold[1066] indeed considers that a large part of the present-day lichens were almost certainly already evolved at the end of the Tertiary period, and that they originated in a warm or probably subtropical climate. As proof of this he cites such genera as _Graphis_, _Thelotrema_ and _Arthonia_[1067] which are numerous in the tropics though rare in the colder European countries; and he sees further proof in the fact that many fruticose and gelatinous lichens do not occur further north than the forest belt, though they are adapted to cold conditions. Several genera that are abundant in the tropics are represented outside these regions by only one or few species, as for instance _Conotrema urceolatum_ and _Bombyliospora incana_.
During the Ice age of the Quaternary period, not many new species can have arisen, and such forms as were not killed off must have been driven towards the south. As the ice retreated the valleys were again stocked with southern forms, and northern species were left behind on mountain tops all over the globe.
In examining therefore the distribution of lichens, it will be found that the distinction between different countries is relative, certain families being more or less abundant in some regions than others, but, in general, nearly all being represented. Certain species are universal, where similar conditions prevail. This is especially true of those species adapted to extreme cold, as that condition, normal in polar regions, recurs even on the equator if the mountains reach the limit of perpetual snow; the vertical distribution thus follows on the lines of the horizontal.
In all the temperate countries we find practically the same families, with some few exceptions; there is naturally more diversity of genera and species. Genera that are limited in locality consist, as a rule, of one or few species. In this category, however, are not included the tropical families or genera which may be very rich in species: these are adapted to extreme conditions of heat and often of moisture, and cannot exist outside tropical or subtropical regions, extreme heat being more restricted as to geographical position than extreme cold.
In the study of distribution the question which arises as to the place of origin of such widely distributed plants is one that is difficult to solve. Wainio[1068] has attempted the task in regard to _Cladonia_, one of the most unstable genera, the variations of form, which are dependent on external circumstances, being numerous and often bewildering. In his fine monograph of the genus, 132 species are described and 25 of these are cosmopolitan.
The distribution of Phanerogams is connected, as Wainio points out, with causes anterior to the present geological era, but this cannot be the case in a genus so labile and probably so recent as _Cladonia_, though some of the species have existed long enough to spread and establish themselves from pole to pole. Endemic species, or those that are confined to a comparatively limited area, are easily traced to their place of origin, that being generally the locality where they are found in most abundance, and as a general rule in the centre of that area, though there may be exceptions: a plant for instance that originated on a mountain would migrate only in one direction—towards the regions of greater cold.
The difficulty of determining the primitive stations of cosmopolitan, or of widely spread, species is much greater, but generally they also may be referred to their area of greatest abundance. Thus a species may occur frequently in one continent and but rarely in another, even where the conditions of climate, etc., are largely comparable. It may therefore be inferred that the plant has not yet reached the full extent of possible distribution in the less frequented area. As examples of this, Wainio cites, among other instances, _Cladonia papillaria_, which has a very wide distribution in Europe, but, as yet, has been found only in the eastern parts of North America; and _Cl. pycnoclada_, a plant which braves the climate of Cape Horn and the Falkland Islands, but has not travelled northward beyond temperate North America: the southern origin of that species is thus plainly indicated. Wainio also finds that evidence of the primitive locality of a very widely spread species may be obtained by observing the locality of species derived from it, which are as yet of limited distribution; presumably these arose in the ancestral place of origin, though this indication is not always to be relied on. If, however, the ancestral plant has given rise to several of these rarer related species, those of them that are most closely allied to the primitive plant would be found near to it in the original locality.
A detailed account of species distribution according to these indications is given by Wainio and is full of interest. No such attempt has been made to deal with any other group, and the distribution of genera and species can only be suggested. An exhaustive comparison of the lichens of different regions is beyond the purpose of our study and is indeed impossible as, except in some limited areas, or for certain species, the occurrence and distribution are not fully known. It is in any case only tentatively that genera or species can be described as local or rare, until diligent search has been made for them over a wider field. The study of lichens from a floristic point of view lags behind that of most other groups of plants. The larger lichen forms have received more attention, as they are more evident and more easily collected; but the more minute species are not easily detected, and, as they are largely inseparable from their substratum of rocks, or trees, etc., on which they grow, they are often difficult to collect. They are also in many instances so indefinite, or so alike in outward form, that they are liable to be overlooked, only a microscopic examination revealing the differences in fruit and vegetative structure.
Though much remains to be done, still enough is known to make the geographical distribution of lichens a subject of extreme interest. It will be found most instructive to follow the usual lines of treatment, which give the three great divisions: the Polar, the Temperate and the Tropical regions of the globe.
B. LICHENS OF POLAR REGIONS
Strictly speaking, this section should include only lichens growing within the Polar Circles; but in practice the lichens of the whole of Greenland and those of Iceland are included in the Arctic series, as are those of Alaska: the latitudinal line of demarcation is not closely adhered to. With the northern lichens may also be considered those of the Antarctic continent, as well as those of the islands just outside the Antarctic Circle, the South Shetlands, South Orkneys, Tierra del Fuego, South Georgia and the Falkland Islands. During the Glacial period, the polar forms must have spread with the advancing cold; as the snow and ice retreated, these forms have been left, as already stated, on the higher colder grounds, and representatives of polar species are thus to be found very far from their original haunts. There are few exclusively boreal genera: the same types occur at the Poles as in the higher subtemperate zones. One of the most definitely polar species, for instance, _Usnea_ (_Neuropogon_) _melaxantha_ grows in the whole Arctic zone, and, in the Antarctic, is more luxuriant than any other lichen, but it has also been recorded from the Andes in Chili, Bolivia and Peru, and from New Zealand (South Island).
Cold winds are a great feature of both poles, and the lichens that by structure or habit can withstand these are the most numerous; those that have a stout cortical layer are able to resist the low temperatures, or those that grow in tufts and thus secure mutual protection. In Arctic and Subarctic regions, 495 lichens have been recorded, most of them crustaceous. Among the larger forms the most frequently met are certain species of _Peltigera_, _Parmelia_, _Gyrophora_, _Cetraria_, _Cladonia_, _Stereocaulon_ and _Alectoria_. Among smaller species _Lecanora tartarea_ spreads everywhere, especially over other vegetation, _Lecanora varia_ reaches the farthest limits to which wood, on which it grows, has drifted, and several species of _Placodium_ occur constantly, though not in such great abundance. Over the rocks spread also many crustaceous Lecideaceae too numerous to mention, one of the most striking being the cosmopolitan _Rhizocarpon geographicum_.
Wainio[1069] has described the lichens collected by Almquist at Pitlekai in N.E. Siberia just on the borders of the Arctic Circle, and he gives a vivid account of the general topography. The snow lies on the ground till June and falls again in September, but many lichens succeed in growing and fruiting. It is a region of tundra and sand, strewn more or less with stones. Most of the sand is bare of all vegetation; but where mosses, etc., have gained a footing, there are also a fair number of lichens: _Lecanora tartarea_, _Psoroma hypnorum_, with _Lecideae_, _Parmeliae_, _Cladoniae_, _Stereocaulon alpinum_, _Solorina crocea_, _Sphaerophorus globosus_, _Alectoria nigricans_ and _Gyrophora proboscidea_. Some granite rocks in that neighbourhood rise to a height of 200 ft., and though bare of vegetation on the north side, yet, in sheltered nooks, several species are to be found. Stunted bushes of willow grow here and there, and on these occur always the same species: _Placodium ferrugineum_, _Rinodina archaea_, _Buellia myriocarpa_ and _Arthopyrenia punctiformis_. Some species such as _Sphaerophorus globosus_, _Dactylina arctica_ (a purely Arctic genus and species) and _Thamnolia vermicularis_ are so abundant that they bulk as largely as other better represented genera such as _Cladoniae_, _Lecanorae_ or _Lecideae_. On the soil, _Lecanorae_ cover the largest areas.
Wainio determined a large number of lichens with many new species, but the region is colder than that of Lappland, and trees with tree-lichens are absent, with the exception of those given above. In Arctic Siberia, Elenkin[1070] discovered a new lichen _Placodium subfruticulosum_ which scarcely differs from Darbishire’s[1071] Antarctic species _Pl. fruticulosum_ (or _P. regale_); both are distinguished by the fruticose growth of the thallus, for which reason Hue[1072] placed them in a new genus, _Polycauliona_.
The Antarctic Zone and the neighbouring lands are less hospitable to plant life than the northern regions, and there is practically no accumulation of detritus. Collections have been made by explorers, and several lists have been published which include a marvellous number of species common to both Poles, if the subantarctic lands are included in the survey. An analytic study of the various lists has been published by Darbishire[1073]. He recognizes 106 true Antarctic lichens half of which are Arctic as well. The greater number are crustaceous and are plants common also to other lands though a certain number are endemic. The most abundant genera in species as well as individuals are _Lecidea_ and _Lecanora_. Several bright yellow species of _Placodium_—_Pl. elegans_, _Pl. murorum_, etc., are there as at the North Pole. Among the larger forms, _Parmeliae_, _Cetrariae_, and _Cladoniae_ are fairly numerous; _Usneae_ and _Ramalinae_ rather uncommon, while members of the Stictaceae are much more abundant than in the North. The common species of _Peltigera_ also occur in Antarctica, though _P. aphthosa_ and _P. venosa_ are wanting; both of these latter are boreal species. Darbishire adds that lichens have so great a capacity to withstand cold, that they are only checked by the snow covering, and were bare rocks to be found at the South Pole, he is sure lichens would take possession of them. The most southerly point at which any plant has been found is 78° South latitude and 162° East longitude, in which locality the lichen _Lecanora subfusca_ was collected by members of Scott’s Antarctic expedition (1901-1904) at a height of 5000 ft.
A somewhat different view of the Antarctic lichen flora is indicated by Hue[1072] in his account of the plants brought back by the second French Antarctic Expedition. The collection was an extremely favourable and important one: great blocks of stone with their communities of lichens were secured, and these blocks were entirely covered, the crustaceous species, especially, spreading over every inch of space.
Hue determined 126 species, but as 15 of these came from the Magellan regions only 111 were truly Antarctic. Of these 90 are new species, 29 of them belonging to the genus _Buellia_. Hue considers, therefore, that in Antarctica there is a flora that, with the exception of cosmopolitan species, is different from every other, and is special to these southern regions. Darbishire himself described 34 new Antarctic species, but only 10 of these are from true Antarctica; the others were collected in South Georgia, the Falkland Islands or Tierra del Fuego. Even though many species are endemic in the south, the fact remains that a remarkable number of lichens which occur intermediately on mountain summits are common to both Polar areas.
C. LICHENS OF THE TEMPERATE ZONES
Regions outside the Polar Circles which enjoy, on the whole, cool moist climates, are specially favourable to lichen growth, and the recorded numbers are very large. The European countries are naturally those in which the lichen flora is best known. Whereas polar and high Alpine species are stunted in growth and often sterile, those in milder localities grow and fruit well, and the more highly developed species are more frequent. _Parmeliae_, _Nephromae_, _Usneae_ and _Ramalinae_ become prominent, especially in the more northern districts. Many Arctic plants are represented on the higher altitudes. A comparison has been made between the lichens of Greenland and those of Germany: of 286 species recorded for the former country, 213 have been found in Germany, the largest number of species common to both countries being crustaceous. Lindsay[1074] considered that Greenland lichens were even more akin to those of Scandinavia.
There is an astonishing similarity of lichens in the Temperate Zone all round the world. Commenting on a list of Chicago lichens by Calkins[1075], Hue[1076] pointed out that with the exception of a few endemic species they resemble those of Normandy. The same result appears in Bruce Fink’s[1077] careful compilation of Minnesota lichens, which may be accepted as typical of the Eastern and Middle States of North Temperate America. The genera from that region number nearly 70, and only two of these, _Omphalaria_ and _Heppia_, are absent from our British Flora. The species naturally present much greater diversity. Very few Graphideae are reported. In other States of North America there occurs the singular aquatic lichen, _Hydrothyria venosa_, nearly akin to _Peltigera_.
If we contrast American lichens with these collected in South Siberia near Lake Baikal[1078], we recognize there also the influence of temperate conditions. Several species of _Usnea_ are listed, _U. barbata_, _U. florida_, _U. hirta_ and _U. longissima_, all of them also American forms, _U. longissima_ having been found in Wisconsin. _Xanthoria parietina_, an almost cosmopolitan lichen, is absent from this district, and is not recorded from Minnesota. The opinion[1079] in America is that it is a maritime species: Tuckerman gives its habitat as “the neighbourhood of a great water,” and reports it from near Lake Superior. In our country it grows at a good distance from the sea, in Yorkshire dales, etc., but all our counties would rank as maritime in the American sense. _Lecanora tartarea_ which is rare in Minnesota is also absent from the Lake Baikal region. It occurs frequently both in Arctic and in Antarctic regions, and is probably also somewhat maritime in habitat. Many of the _Parmeliae_, _Nephromiae_ and _Peltigerae_, common to all northern temperate climes, are Siberian as are also _Cladoniae_ and many crustaceous species. There is only one _Sticta_, _St. Wrightii_, a Japanese lichen, recorded by Wainio from this Siberian locality.
A marked difference as regards species is noted between the Flora of Minnesota and that of California. Herre[1080] has directed attention to the great similarity between the lichens of the latter state and those of Europe: many European species occur along the coast and nowhere else in America so far as is yet known; as examples he cites, among others, _Calicium hyperellum_, _Lecidea quernea_, _L. aromatica_, _Gyrophora polyrhiza_, _Pertusaria amara_, _Roccella fuciformis_, _R. fucoides_ and _R. tinctoria_. The Scandinavian lichen, _Letharia vulpina_, grows abundantly there and fruits freely; it is very rare in other parts of America. Herre found, however, no specimens of _Cladonia rangiferina_, _Cl. alpestris_ or _Cl. sylvatica_, nor any species of _Graphis_; he is unable to explain these anomalies in distribution, but he considers that the cool equable climate is largely responsible: it is so much more like that of the milder countries of Europe than of the states east of the Sierra Nevada. His contention is supported by a consideration of Japanese lichens. With a somewhat similar climate there is a great preponderance of European forms. Out of 382 species determined by Nylander[1081], 209 were European. There were 17 _Graphideae_, 31 _Parmeliae_, and 23 _Cladoniae_, all of the last named being European. These results of Nylander’s accord well with a short list of 30 species from Japan compiled by Müller[1082] at an earlier date. They were chiefly crustaceous tree-lichens; but the _Cladoniae_ recorded are the familiar British species _Cl. fimbriata_, _Cl. pyxidata_ and _Cl. verticillata_.
With the Japanese Flora may be compared a list[1083] of Maingay’s lichens from China, 35 in all. _Collema limosum_, the only representative of Collemaceae in the list, is European, as are the two species of _Ramalina_, _R. gracilenta_ and _R. pollinaria_; four species of _Physcia_ are European, the remaining _Ph. picta_ being a common tropical or subtropical plant. _Lecanora saxicola_, _L. cinerea_, _Placodium callopismum_ and _Pl. citrinum_ are cosmopolitan, other _Lecanorae_ and most of the _Lecideae_ are new. _Graphis scripta_, _Opegrapha subsiderella_ and _Arthonia cinnabarina_—the few Graphideae collected—are more or less familiar home plants. Among the Pyrenocarpei, _Verrucaria_ (_Pyrenula_) _nitida_ occurs; it is a widely distributed tree-lichen.
It is unnecessary to describe in detail the British lichens. Some districts have been thoroughly worked, others have barely been touched. The flora as a whole is of a western European type showing the influence of the Gulf Stream, though there is also a representative boreal growth on the moorlands and higher hills, especially in Scotland. Such species as _Parmelia pubescens_, _P. stygia_ and _P. alpicola_ recall the Arctic Circle while _Alectoriae_, _Cetrariae_ and _Gyrophorae_ represent affinity with the colder temperate zone.
In the southern counties such species as _Sticta aurata_, _S. damaecornis_, _Phaeographis Lyellii_ and _Lecanora_ (_Lecania_) _holophaea_ belong to the flora of the Atlantic seaboard, while in S.W. Ireland the tropical genera _Leptogidium_ and _Anthracothecium_ are each represented by a single species. The tropical or subtropical genus _Coenogonium_ occurs in Great Britain and in Germany, with one sterile species, _C. ebeneum_. _Enterographa crassa_ is another of our common western lichens which however has travelled eastwards as far as Wiesbaden. _Roccella_ is essentially a maritime genus of warm climates: two species, _R. fuciformis_ and _R. fucoides_, grow on our south and west coasts. The famous _R. tinctoria_ is a Mediterranean plant, though it is recorded also from a number of localities outside that region and has been collected in Australia.
In the temperate zones of the southern hemisphere are situated the great narrowing projections of South Africa and South America with Australia and New Zealand. As we have seen, the Antarctic flora prevails more or less in the extreme southern part of America, and the similarity between the lichens of that country and those of New Zealand is very striking, especially in the fruticulose forms. There is a very abundant flora in the New Zealand islands with their cool moist climate and high mountains. Churchill Babington[1084] described the collections made by Hooker. Stirton[1085] added many species, among others _Calycidium cuneatum_, evidently endemic. Later, Nylander[1086] published the species already known, and Hellbom[1087] followed with an account of New Zealand lichens based on Berggsen’s collections; many more must be still undiscovered. Especially noticeable as compared with the north, are the numbers of Stictaceae which reach their highest development of species and individuals in Australasia. They are as numerous and as prominent as are Gyrophoraceae in the north. A genus of Parmeliaceae, _Hetorodea_, which, like the _Stictae_, bears cyphellae on the lower surface, is peculiar to Australia.
A warm current from the tropical Pacific Ocean passes southwards along the East Coast of Australia, and Wilson[1088] has traced its influence on the lichens of Australia and Tasmania to which countries a few tropical species of _Graphis_, _Chiodecton_ and _Trypethelium_ have migrated. Various unusual types are to be found there also: the beautiful _Cladonia retepora_ (Fig. 71), which spreads over the ground in cushion-like growths, with the genera _Thysanothecium_ and _Neophyllis_, genera of Cladoniaceae endemic in these regions.
The continent of Africa on the north and east is in so close connection with Europe and Asia that little peculiarity in the flora could be expected. In comparing small representative collections of lichens, 37 species from Egypt and 20 from Palestine, Müller[1089] found that there was a great affinity between these two countries. Of the Palestine species, eight were cosmopolitan; among the crustaceous genera, _Lecanorae_ were the most numerous. There was no record of new genera.
The vast African continent—more especially the central region—has been but little explored in a lichenological sense; but in 1895 Stizenberger[1090] listed all of the species known, amounting to 1593, and new plants and new records have been added since that day. The familiar genera are well represented, _Nephromium_, _Xanthoria_, _Physcia_, _Parmelia_, _Ramalina_ and _Roccella_, some of them by large and handsome species. In the Sahara Steiner[1091] found that genera with blue-green algae such as the Gloeolichens were particularly abundant; _Heppia_ and _Endocarpon_ were also frequent. Algeria has a Mediterranean Flora rather than tropical or subtropical. Flagey[1092] records no species of _Graphis_ for the province of Constantine, and only 22 species of other Graphideae. Most of the 519 lichens listed by him there are crustaceous species. South America stretches from the Tropics in the north to Antarctica in the south. Tropical conditions prevail over the central countries and tropical tree-lichens, Graphidaceae, Thelotremaceae, etc. are frequent; further West, on the Pacific slopes, _Usneae_ and _Ramalinae_ hang in great festoons from the branches, while the foliose _Parmeliae_ and _Stictae_ grow to a large size on the trunks of the trees.
Wainio’s[1093] _Lichens du Brésil_ is one of the classic systematic books and embodies the writer’s views on lichen classification. There are no new families recorded though a number of genera and many species are new, and, so far as is yet known, these are endemic. Many of our common forms are absent; thus _Peltigera_ is represented by three species only, _P. leptoderma_, _P. spuriella_ and _P. Americana_, the two latter being new species. _Sticta_ (including _Stictina_) includes only five species, and _Coenogonium_ three. There are 39 species of _Parmelia_ with 33 of _Lecanora_ and 68 of _Lecidea_, many of them new species.
D. LICHENS OF TROPICAL REGIONS
In the tropics lichens come under the influence of many climates: on the high mountains there is a region of perpetual snow, lower down a gradual change to temperate and finally to tropical conditions of extreme heat, and, in some instances, extreme moisture. There is thus a bewildering variety of forms. By “tropical” however the warmer climate is always implied. Several families and genera seem to flourish best in these warm moist conditions and our familiar species grow there to a large size. Among crustaceous families Thelotremaceae and Graphidaceae are especially abundant, and probably originated there. In the old comprehensive genus _Graphis_, 300 species were recorded from the tropics. It should be borne in mind that _Trentepohlia_, the alga that forms the gonidia of these lichens, is very abundant in the tropics. _Coenogonium_, a genus containing about twelve species and also associated with _Trentepohlia_, is scarcely found in Europe, except one sterile species, _C. ebeneum_. Other species of the genus have been recorded as far north as Algeria in the Eastern Hemisphere and Louisiana in the Western, while one species, _C. implexum_, occurs in the southern temperate zone in Australia and New Zealand.
Of exclusively tropical lichens, the Hymenolichens are the most noteworthy. They include three genera, _Cora_, _Corella_ and _Dictyonema_, the few species of which grow on trees or on the ground both in eastern and western tropical countries.
Other tropical or subtropical forms are _Oropogon loxensis_, similar to _Alectoria_ in form and habit, but with one brown muriform spore in the ascus; it is only found in tropical or subtropical lands. _Physcidia Wrightii_ (Parmeliaceae) is exclusively a Cuban lichen. Several small genera of Pyrenopsidaceae such as _Jenmania_ (British Guiana), _Paulia_ (Polynesia) and _Phloeopeccania_ (South Arabia) seem to be confined to very hot localities. On the other hand Collemaceae are rare: Wainio records from Brazil only four species of _Collema_, with nine of _Leptogium_.
Among Pyrenolichens, Paratheliaceae, Mycoporaceae and Astrotheliaceae are almost exclusively of tropical distribution, and finally the leaf lichens with very few exceptions. These follow the leaf algae, _Mycoidea_, _Phycopeltis_, etc., which are so abundant on the coriaceous long-lived green leaves of a number of tropical Phanerogams. All the Strigulaceae are epiphytic lichens. _Phyllophthalmaria_ (Thelotremaceae) is also a leaf genus; one of the species, _Ph. coccinea_, has beautiful carmine-red apothecia. The genera of the tropical family Ectolechiaceae also inhabit leaves, but they are associated with Protococcaceae; one of the genera _Sporopodium_[1094] is remarkable as having hymenial gonidia. Though tropical in the main, epiphyllous lichens may spread to the regions beyond: _Sporopodium Caucasium_ and a sterile _Strigula_ were found by Elenkin and Woronichin[1095] on leaves of _Buxus sempervirens_ in the Caucasus, well outside the tropics.
_Pilocarpon_, an epiphytic genus, is associated with Protococcaceae; one of the species, _P. leucoblepharum_, spreads from the bark to the leaves of pine-trees; it is widely distributed and has also been reported in the Caucasus[1096]. _Chrysothrix_, in which the gonidia belong to the algal genus _Palmella_, grows on Cactus spines in Chili, and may also rank as a subtropical epiphyllous lichen.
A series of lichens from the warm temperate region of Transcaucasia investigated by Steiner[1097] were found to be very similar to those of Central Europe. Lecanoraceae were, however, more abundant than Lecideaceae and Verrucariaceae were comparatively rare.
Much of Asia lies within tropical or subtropical influences. Several regions have received some amount of attention from collectors. From Persia there has been published a list of 59 species determined by Müller[1098]; several of them are Egyptian or Arabian plants, 15 are new species, but the greater number are European.
A small collection of 53 species from India, near to Calcutta, published by Nylander[1099], included a new genus of Caliciaceae, _Pyrgidium_ (_P. bengalense_), allied to _Sphinctrina_. He also recorded _Ramalina angulosa_ in African species, along with _R. calicaris_, _R. farinacea_ and _Parmelia perlata_, f. _isidiophora_, which are British. Other foliose forms, _Physcia picta_, _Pyxine Cocoës_ and _P. Meissnerii_ are tropical or subtropical; along with these were collected crustaceous tropical species belonging to _Lecanorae_, _Lecideae_, Graphideae, etc.
Leighton[1100] published a collection of Ceylon lichens and found that Graphideae predominated. Nylander[1101] came to the same conclusion with regard to lichens referred to him: out of 159 species investigated from Ceylon, there were 36 species of Graphideae. In another list[1102] of Labuan, Singapore and Malacca lichens, 164 in all, he found that 56 belonged to the Graphidei, 36 to Pyrenocarpei, 14 to Thelotremei and 11 to Parmelei; only 15 species were European.
On the whole it is safe to conclude from the above and other publications that the exceptional conditions of the tropics have produced many distinctive lichens, but that a greater abundance both of species and individuals is now to be found in temperate and cold climates.
III. FOSSIL LICHENS
In pronouncing on the great antiquity of lichens, proof has been adduced from physiological rather than from phytogeological evidence. It would have been of surpassing interest to trace back these plants through the ages, even if it were never possible to assign to any definite period the first symbiosis of the fungus and alga; but among fossil plants there are only scanty records of lichens and even these few are of doubtful determination.
The reason for this is fairly obvious: not only are the primitive thalline forms too indistinct for recognizable preservation, but all lichens are characterized by the gelatinous nature of the hyphal or of the algal membranes which readily imbibe water. They thus become soft and flaccid and unfit to leave any impress on sedimentary rocks. It has also been pointed out by Schimper[1103] that while deciduous leaves with fungi on them are abundant in fossil beds, lichens are entirely wanting. These latter are so firmly attached to the rocks or trees on which they grow that they are rarely dislodged, and form no part of wind- or autumn-fall. Trunks and branches of trees lose their bark by decay long before they become fossilized and thus all trace of their lichen covering disappears.
The few records that have been made are here tabulated in chronological order:
1. PALAEOZOIC. Schimper decides that there are no records of lichens in the earlier epochs. Any allusions[1104] to their occurrence are held to be extremely vague and speculative.
2. MESOZOIC. Braun[1105] has recorded a _Ramalinites lacerus_ from the Keuper sandstone at Eckersdorf, though later[1106] he seemed to be doubtful as to his determination. One other lichen, an _Opegrapha_, has been described[1107] from the chalk at Aix.
3. CAINOZOIC. In the brown-coal formations of Saxony Engelhardt[1108] finds two lichens: _Ramalina tertiaria_, a much branched plant, the fronds being flat and not channelled “and of further interest that it is attached to a carbonized stem.” The second form, _Lichen dichotomus_, has a dichotomously branching strap-shaped frond. “There is sufficient evidence that these fronds were cylindrical and that the width is due to pressure. In one place a channel is visible, filled with an ochraceous yellow substance.”
Other records on brown coal or lignite are: _Verrucarites geanthricis_[1109] Goepp., somewhat similar to _Pyrenula nitida_, found at Muskau in Silesia; _Opegrapha Thomasiana_[1110] Goepp., near to _Opegrapha varia_, and _Graphis scripta succinea_ Goepp.[1111] on a piece of lignite in amber beds, all of them doubtful.
Schimper has questioned, as he well might, Ludwig’s[1112] records from lignite from the Rhein-Wetterau Tertiary formations; these are: _Cladonia rosea_, _Lichen albineus_, _L. diffissus_ and _L. orbiculatus_; he thinks they are probably fungus mycelia. Another lichen, a _Parmelia_ with apothecia, which recalls somewhat _P. saxatilis_ or _P. conspersa_, collected by Geyler also in the brown coal of Wetterau is accepted by Schimper[1113] as more trustworthy.
More authentic also are the lichens from the amber beds of Königsberg and elsewhere collected by Goeppert and others. These deposits are Cainozoic and have been described by Goeppert and Menge[1114] as middle Miocene. Schimper gives the list as: _Parmelia lacunosa_ Meng. and Goepp., fragments of thallus near to _P. saxatilis_; _Sphaerophorus coralloides_; _Cladonia divaricata_ Meng. and Goepp.; _Cl. furcata_; _Ramalina calicaris_ vars. _fraxinea_ and _canaliculata_; _Cornicularia aculeata_, _C. subpubescens_ Goepp., _C. ochroleuca_, _C. succinea_ Goepp., and _Usnea barbata_ var. _hirta_. Schimper rather deprecates specific determinations when dealing with such imperfect fragments.
In a later work Goeppert and Menge[1114] state that they have found twelve different amber lichens and that among these are _Physcia ciliaris_, _Parmelia physodes_ and _Graphis_ (probably _G. scripta succinea_) along with _Peziza resinae_ which is more generally classified among lichens as _Lecidea_ (_Biatorella_) _resinae_.
Another series of lichens found in recent deposits in North Europe has been described by Sernander[1115] as “subfossil.” While engaged on the investigations undertaken by the Swedish Turf-Moor Commission, he noted the alternation of slightly raised _Sphagnum_ beds with lower-lying stretches of _Calluna_ and lichen moor—in some instances dense communities of _Cladonia rangiferina_. In time the turf-forming _Sphagnum_ overtopped and invaded the drier moorland, covering it with a new formation of turf. Beneath these layers of “regenerated turf” were found local accumulations of blackened remains of the _Cladonia_ still recognizable by the form and branching. Some specimens of _Cetraria islandica_ were also determined.
Of especial lichenological interest in these northern regions was the Calcareous Tufa or Calc-sinter in which Sernander also found subfossil lichens—distinct impressions of _Peltigera_ spp. and the foveolae of endolithic calcicolous species.
In another category he has placed _Ramalina fraxinea_, _Graphis_ sp. and _Opegrapha_ sp., traces of which were embedded with drift in the Tufa. In the two Graphideae the walls of apothecia and pycnidia were preserved. Sernander considers their presence of interest as testifying to warmer conditions than now prevail in these latitudes.