Observations of a Naturalist in the Pacific Between 1896 and 1899, Volume 2 Plant-Dispersal

CHAPTER XXII

Chapter 647,500 wordsPublic domain

THE ERA OF THE ENDEMIC GENERA (_continued_)

THE COMPOSITÆ AND LOBELIACEÆ (_continued_)

THE AGE OF THE TREE-LOBELIAS

The distribution of the arborescent Lobeliaceæ.—On the upper flanks of Ruwenzori.—The Lobeliaceæ of the Hawaiian Islands.—The Lobeliaceæ of the Tahitian or East Polynesian region.—The capacities for dispersal.—The explanation of the absence of the early Lobeliaceæ from West Polynesia.—The other Hawaiian endemic genera.—The Fijian endemic genera.—Summary.

THE Lobeliaceæ rank with the Compositæ in the prominence of their position in the early Pacific floras. Though absent, as far as is known, from Fiji, they are represented in Hawaii by 58 species, all endemic and belonging to six genera, of which five are not found elsewhere. All possess, as Hillebrand remarks, a woody stem, by far the greater number being either tall shrubs, 5 or 6 feet high, or small trees, 10 to 20 feet or more in height. In the East Polynesian or Tahitian region, the order is represented by two genera containing in all five known species and restricted to those islands. One genus is common to the islands of Tahiti and Rarotonga, and the other is confined to Raiatea. The species may be shrubby or arborescent.

It was for some time considered that the oceanic archipelagoes of the Pacific were the exclusive centres of these singular arborescent Lobeliaceæ (I am here quoting Baillon in his _Natural History of Plants_). And indeed this idea would receive some support from the circumstance that Dr. Hillebrand, in his work on Hawaii, says little or nothing about the affinities or general relations of plants which he enthusiastically termed “the pride of our flora.” His death in 1886 deprived his work of its crowning piece, a discussion of “the interesting questions of the origin and development of the Hawaiian flora” (see the Editor’s Introduction, p. ix.). In no group of plants is this want more keenly felt than with the Lobeliaceæ. Yet in his time the explorations had yet to be made that could set the student of plant-distribution on the road to investigate this problem.

It was true, no doubt, that types analogous to those of the Hawaiian Lobeliaceæ were known from the American and African continents. Thus Oliver in his _Flora of Tropical Africa_, published in 1877, gives an account of the species of Lobelia then known from the mountains of this region. The genus was, however, not entirely confined to mountainous districts, but it would almost seem that most of the high mountains of Equatorial Africa had their peculiar species, some of them being tree-like and others shrubby. Two mountain species were recorded from Abyssinia, one of them from an elevation of 11,000 to 13,000 feet and growing to a height of 12 to 15 feet, the other from an altitude of about 8,000 feet; another, Lobelia Deckenii, attaining a height of 4 feet, was recorded from the uplands of Kilimanjaro, 12,000 to 13,000 feet above the sea, and yet another from the mountains of Fernando Po, at an altitude of 9,000 feet. So again, in the case of the American continent, Hemsley, writing in 1885 (_Intr. Bot. Chall. Exped._, p. 32), speaks of arborescent species of the American genera Centropogon, Siphocampylus, &c.; and Baillon in his _Natural History of Plants_ (Engl. edit. viii. 350) refers to the similar Tupas and Haynaldias from South America. But what the student of plant-distribution looked for was not merely the occurrence of “tree-lobelias” in other parts of the world, but also the reproduction of these wonderful plants under the same conditions and on the same scale as those familiar to him on the Hawaiian mountains. He has accordingly had to wait for the results of the more recent explorations of the mountains of Central Africa in order to obtain his wish.

On the upper flanks of Ruwenzori, Kilimanjaro, and Kenya, at elevations of 9,000 to 13,000 feet and reaching to the snow-line, there flourish in boggy portions of the forest arborescent Lobeliaceæ that attain a height of 15 or 20 feet. They have the habit sometimes of a Dracæna and sometimes of an Aloe, and do not exhibit the branching trunks so characteristic of the Hawaiian genus of Clermontia. They all belong, however, to the genus Lobelia, and thus do not display the extensive differentiation of the endemic genera of Hawaii. Nor, apparently, has there been the same degree of formative energy in the development of species, since only about half a dozen species are hitherto known. We find, however, produced on these lofty mountains of Equatorial Africa the same climatic conditions under which the arborescent Lobeliaceæ flourish in Hawaii, namely, the very humid atmosphere, the heavy rainfall, and the mild temperature; and if there are important contrasts in their character and in the amount of differentiation which they have undergone in the two regions, the one a continental and the other an insular region, it will be from such contrasts that some of the most interesting results of this comparison of a mountain of Central Africa with an island of the open Pacific will be ultimately derived (see Sir H. Johnston’s _Uganda Protectorate_, 1902, and _Kilimanjaro Expedition_, 1886; also _Trans. Linn. Soc. Bot._, ser. 2, vol. 2, p. 341.)

THE LOBELIACEÆ OF THE HAWAIIAN AND OF THE EAST POLYNESIAN OR TAHITIAN ISLANDS.[1]

HAWAIIAN ISLANDS.

EAST POLYNESIAN OR TAHITIAN ISLANDS.

+-----------+-----+-------------+-------------+------------+-------------+-----------+ |Sclerotheca| 4 | Endemic in |{Tahiti, | 6 to 25 | 1,500 to | Humid | | | | E.Polynesia.|{Rarotonga. | feet. | 3,000 feet. | wooded | | | | | | | | slopes. | | | | | | | | | |Apetahia. | 1 | Endemic. | Raiatea. | 3 to 6 | In the | | | | | | | feet. | mountains. | | | | | | | | Elevation of| | | | | | | | island 3,400| | | | | | | | feet. | | +-----------+-----+-------------+-------------+------------+-------------+-----------+ Footnote 1:

The materials are nearly all derived from the works of Hillebrand and Drake del Castillo. Some of those relating to the elevations in Hawaii are supplemented from my notes. All the genera are endemic except Lobelia, of which all the species are apparently endemic, excepting perhaps one, which, according to Hillebrand, resembles greatly a species from the Liukiu Islands.

Footnote 2:

The range of the heights of different species of Clermontia is from 5 or 6 feet for shrubs to 25 feet for trees.

Footnote 3:

The heights attained by different species of Cyanea range from 3 or 4 feet to between 30 and 40 feet, thus:—

In 8 species 3 to 6 feet. In 9 species 6 to 10 feet. In 7 species 10 to 15 feet. In 3 species 15 to 25 feet. In 1 species 30 to 40 feet.

THE LOBELIACEÆ OF THE HAWAIIAN ISLANDS.

Having thus prepared the way, I will proceed to the discussion of the Hawaiian Lobeliaceæ, dealing first with their “station.” Their vertical distribution is well illustrated in the large and lofty island of Hawaii. Whilst the woody Compositæ, as before described, are most at home on the open-wooded and often scantily-forested slopes between 5,000 and 9,000 feet, the Lobeliaceæ are most characteristic of the middle or true forest zone that extends from 2,000 or 3,000 feet to between 5,000 and 6,000 feet above the sea. This lies within the region of clouds and mists, and it is here that the rain-belt or area of greatest rainfall is situated, the annual amount averaging probably 150 to 200 inches. It is in such humid conditions that, as Hillebrand observes, trees and jungle are developed in greatest luxuriance; and it is here that “the Lobeliaceæ exhibit their most striking forms.” The traveller, as he ascends the mountains, finds the Tree-Lobelias in the region of mist and rain-cloud; and he is lucky if he escapes the usual downpour and encounters only a fine drizzling rain.

The mild climate of this region is indicated by a mean annual temperature ranging probably with elevation from 65° to 55° F. It is secure from the frosts of the upper slopes of the mountain; whilst at the same time it is above the regions of tropical heat. There is, however, no doubt that when the forests extended to the coasts, as they occasionally do now on the north side of Hawaii, the Lobeliaceæ occurred much lower down than they do at present, though still only attaining their greatest development in size and number in the higher levels. Thus, at rare intervals, I noticed in the forests of Hamakua and Kohala, where they descended to the coasts, species of Clermontia at an elevation of only 500 or 600 feet above the sea.

Probably in no part of the Hawaiian Islands are the conditions under which the “Tree-Lobelias” thrive better illustrated than on the higher slopes of Mount Eeka, a bulky mountain mass about 6,000 feet in height, forming the western portion of Maui. Its flat top, as Hillebrand observes, is wrapped in a cloud of mist nearly the whole year. On the boggy surface of the summit, where Acæna exigua gives a tussocky appearance, and Sphagnum or bog-moss abounds, flourish Cyperaceæ, Lycopods, and Selaginellæ; and here Drosera longifolia and a peculiar species of marsh violet (Viola mauiensis) find a home. The upper slopes, down to 4,000 feet, present similar moist conditions, and here in an open-wooded district, associated with Cyrtandræ, Marattias, and true Tree-Ferns, the ground being covered with Lycopods, the “Tree-Lobelias” abound. I noted four kinds within two hundred yards. Of the humidity of the upper slopes of Mount Eeka I have a very vivid recollection, and my experience of passing a night on that mountain is described in Chapter XIX.

The Lobeliaceæ, as Hillebrand remarks, occur invariably as isolated individuals. I was often struck, however, with the preference the genera showed for particular localities. Thus, Clermontia is well represented on the western slopes of Mount Eeka, Delissea on the northern slopes of Hualalai (3,800 to 4,500 feet), Cyanea on the Hamakua slopes of Mauna Kea (2,300 to 4,100), and Lobelia on the southern slopes of Mauna Loa behind Punaluu (2,000 to 3,500 feet).

To the student of geographical distribution the Hawaiian Lobeliaceæ are of especial interest. Mr. Hemsley observes that they have their greatest affinities in America (_Intr. Bot. Chall. Exped._, p. 68). M. Drake del Castillo, in his “Mémoire couronné par l’Académie des Sciences” (Paris, 1890), remarks that these plants connect Hawaii with America just as the Goodeniaceæ link the same group with Australia. This is what we might have expected since the centre of the order is in America, principally in the Mexican and Andine regions (Drake del Castillo, _Flore Polyn. Franc._, xi.).

Though five out of the six genera are endemic, the sixth, that of Lobelia, has a world-wide distribution. Here then, we have a genus that belongs strictly to the next or second stage of the plant-stocking of the Hawaiian Group, namely, when the non-endemic genera now containing endemic species were introduced. As with the Composite genera, Campylotheca and Lipochæta, Lobelia marks the beginning of the new or the close of the old era. It is, however, necessary to point out that many of the conditions favouring luxuriant and rank vegetable growth are pre-eminently represented in the zone of the Lobeliaceæ. In these soft-stemmed plants with their copious milky sap and large fleshy flowers, sometimes two or three inches long, the very redundancy of growth would tend both to exaggerate and to disguise the generic distinctions. To the ordinary observer these “Tree-Lobelias” call up vague notions of a flora of a bygone age, and by their _bizarre_ appearance he might with some excuse be led to give play to his imagination when describing them; but the systematic botanist, seeing through their disguise, frames rather more prosaic notions of their antiquity and degree of differentiation. According to my view, the first Hawaiian Lobeliaceæ occupied open, exposed localities such as are held by the decadent genus Brighamia now, and acquired their monstrous form in the humid forests of a later age. (See Perkins in Note 80.)

In his monograph on the Campanulaceæ (Engler’s _Nat. Pflanz. Fam._, teil 4, abth. 5, 1894), S. Schönland, speaking of the sub-family Lobelioideæ, places the seven endemic Hawaiian and Tahitian genera in a group by themselves. Though, as he observes, the Hawaiian tree-forms appear at first sight to constitute a natural group, they cannot be sharply distinguished from other forms, and even in habit come near some Indian and Abyssinian types of Lobelia. In their treatment, he says, they should all go together, and he does not approve of the endeavours of some botanists to isolate one of them (Brighamia) from the rest and to connect it with the Australian genus Isotoma.

It is also to be noted that whilst four of the Hawaiian genera are more or less dispersed over the group, one (Brighamia) with only one species is confined to the islands of Molokai and Niihau, the double habitat being suggestive of its approaching extinction. Another (Rollandia) with six species is restricted to the island Oahu. Cyanea, which possesses twenty-eight out of the total of fifty-eight species, may, from the point of view of its formative energy, be regarded as in its prime. It is thus apparent that, as with the Compositæ, the early Lobeliaceous immigrants were not all contemporaneous arrivals.

DISTRIBUTION OF THE LOBELIACEÆ IN THE HAWAIIAN ISLANDS.[4]

Column headings:

A: Brighamia. B: Lobelia. C: Clermontia. D: Rollandia. E: Delissea. F: Cyanea. G: Total.

+----------------------------------+----+----+----+----+----+----+----+ | Hawaiian Lobeliaceæ. | A | B | C | D | E | F | G | +----------------------------------+----+----+----+----+----+----+----+ | Species confined to one island | — | — | 6 | 6 | 4 | 22 | 38 | | Species confined to two islands | 1 | 2 | 2 | — | 2 | 5 | 12 | | Species confined to three islands| — | 1 | 2 | — | 1 | 1 | 5 | | Species generally distributed, | | | | | | | | | but still endemic | — | 2 | 1 | — | — | — | 3 | | +----+----+----+----+----+----+----+ | | 1 | 5 | 11 | 6 | 7 | 28 | 58 | +----------------------------------+----+----+----+----+----+----+----+ Footnote 4:

All the species are endemic.

Another interesting fact of distribution, brought out by an analysis of Hillebrand’s materials and illustrated in the subjoined table, is that out of the fifty-eight Hawaiian species, all of which are endemic, thirty-eight, or 66 per cent., are recorded from only one island. In most of the other cases they are recorded from two or three islands, usually adjacent, like Maui and Molokai; and except in the instance of two species of Lobelia and one species of Clermontia they never range over the length of the group.

These facts speak eloquently of the suspension to a great extent of the agencies of dispersal in recent times within the group. Some corrections of the figures will be rendered necessary by future investigations, but the main conclusion will not be materially affected. Such facts are paralleled in the distribution of the Hawaiian insects, mollusca, &c.; but these matters need only be mentioned here. We might, indeed, have expected, apart from other considerations, that the isolation of the Hawaiian Lobeliaceæ from their kindred in other parts of the world would not have been reproduced within the group itself. This, however, is not the case; and we now see that not only have they been deprived for ages of their means of distribution over the Pacific, but that even within the archipelago their transportal from island to island has been largely suspended. We have before arrived at similar conclusions with regard to the early Compositæ, when we saw that about half the species were not found in more than one island. It is therefore evident that the same great principle regulating the operations of the distributing agencies has influenced to a similar extent both the Compositæ and the Lobeliaceæ of the Hawaiian Group.

THE LOBELIACEÆ OF THE TAHITIAN OR EAST POLYNESIAN REGION.

The order is represented in this region by two endemic genera, Sclerotheca of Tahiti and Rarotonga, and Apetahia of Raiatea. These islands are, however, not sufficiently large for the extensive development of the arborescent Lobeliaceæ, such as we find in Hawaii. The species in both genera are either arborescent or shrubby; but I do not gather that they give any character to the floras of these islands. According to the data given by Drake del Castillo for one of the two peculiar species of Sclerotheca occurring in Tahiti, these plants grow on the humid wooded slopes of the mountains at elevations of 2,000 to 3,000 feet. Whilst in one species the plants attain a height of 10 to 25 feet, in the other they do not exceed 10 feet. Rarotonga possesses a peculiar species of Sclerotheca, 4 to 6 feet high, which was discovered by Cheeseman growing plentifully on the upper slopes of the highest mountain of the island at altitudes of 1,500 to 2,200 feet. The same botanist also came upon a second species of the genus on another mountain in Rarotonga at elevations of 1,000 to 1,500 feet, but it was rare and has not yet been described. The other genus, Apetahia, has only been recorded from Raiatea, where it is represented by a solitary species (6 feet high) growing, according to Nadeaud, in the mountains of that island.

It is apparent that the dispersal of these genera of the Lobeliaceæ amongst the groups of Eastern Polynesia ceased long ago. From the circumstance that Sclerotheca exists in Tahiti and in Rarotonga, which are about 650 miles apart, it may be inferred either that the genus was introduced into this region from outside, or else, which is perhaps more probable, that it was developed in Tahiti whence it was transported to Rarotonga. Hemsley speaks of this Tahitian genus as seemingly marking a former wide extension of the Hawaiian arborescent type of the Lobeliaceæ (_Introd. Bot. Chall. Exped._, p. 68). This is the view that will be adopted in this chapter, and it is precisely the view advocated by Bentham and followed here, in the case of the early Compositæ of the Pacific.

With regard to the absence of these arborescent Lobeliaceæ from the island-groups of the Western Pacific, and notably from Fiji and Samoa, where no members of the order seem to occur, it is probable that, as in the case of the similar distribution of the early Compositæ described in the preceding chapter, this is to be attributed to the fact that the Western Pacific archipelagoes were more or less submerged during the general dispersion of the Compositæ and Lobeliaceæ over the Pacific in the earliest age of the floral history of these islands. The occurrence of the early Compositæ and Lobeliaceæ in Rarotonga, which is almost half-way between Tahiti and Tonga on the outskirts of the Fijian region, sufficiently indicates that they are not lacking in that region from inability to reach there in the past. During the age of general dispersal of these two orders over the Pacific, probably only a few rocky islets, tenanted perhaps by Conifers, marked the situation in the Tertiary period of the present archipelagoes of Fiji and Samoa.

One may note in passing the general absence of these arborescent types of the Lobeliaceæ from Malaya, since they do not seem to have been recorded either from the Owen Stanley Range in New Guinea or from Kinabalu in North Borneo, the highest mountain in the Malayan Islands, or from the mountains of Java.

The consideration of the occurrence of these plants in other tropical or subtropical oceanic islands need not detain us long, since, with the exception of the solitary Lobelia scævolifolia of St. Helena, they seem rarely to be found. This species, which is endemic, is a shrub growing on the upper slopes and summit of the island at elevations of 2,000 to 2,700 feet (_Introd. Bot. Chall. Exped._, p. 40, and Part ii. pp. 54, 76).

There are two herbaceous species of Lobelia in Juan Fernandez, of which one only, according to Hemsley, could be regarded as indigenous. This is a showy Chilian and Peruvian species (Lobelia tupa) noticed by Bertero as very common in 1829 (_Bot. Chall. Exped._, Part iii.). Since, however, it would belong to the present age of plant-dispersal in the Pacific, it does not require further mention here; and indeed it would almost appear, when we bear in mind the geographical position and the history of this island since its discovery in 1563, that even as a truly indigenous plant it is not above suspicion. Lobelias of this type are now amongst the commonest plants of the coast regions of northern Chile, where I noticed some as much as 9 or 10 feet high.

_On the Capacities of Dispersal of the Lobeliaceæ of the Pacific._—Of actual observations, with the exception of the instance of birds pecking at the capsules of our garden Lobelias, I have come upon few that bear directly on this point. When writing of the flora of the Kermadec Group, many years ago, Sir Joseph Hooker referred (_Journ. Linn. Soc. Bot._, vol. i.) to the minute seeds of Lobelia as not adapted for transport unless their minuteness and number fit them for it; but since he associates in this connection the tiny seeds of Metrosideros, which is now represented by a species found all over the Pacific, it would seem that the difficulty in the case of Lobelia is not connected so much with the nature as with the suspension of these means of distribution during the later stages of the plant-stocking of the oceanic islands of the tropical Pacific. It will be gathered from the following remarks that the descendants of the early Pacific Lobeliaceæ are probably as well fitted for dispersal as their ancestors, and that the break in the communication is the ultimate subject for inquiry.

The fruits of the Hawaiian endemic genera are in four out of five cases baccate, with usually fleshy or pulpy contents. Such berries, which are generally yellow, but sometimes bluish in colour, vary in size from about half an inch in Rollandia and Delissea to an inch in Cyanea, and not infrequently to more than an inch in Clermontia. The fruits of Lobelia and Brighamia are capsular and dehiscent. With regard to the two genera of the Society Islands and Rarotonga, the fruits of Sclerotheca are hard-walled capsules, opening by two pores; whilst those of Apetahia are seemingly dry and indehiscent. I do not imagine, therefore, that the character of the fruit has determined to any important degree the distribution of these plants.

Nor is there reason to suppose that the fruits have acquired their baccate character in Hawaii, and that they were originally dry and capsular. Both types of fruit are found among the arborescent Lobeliaceæ of America, with which the Hawaiian genera have their affinities. Centropogon, for instance, which occurs in Central America and in the warm parts of North and South America, has, according to Baillon, a somewhat fleshy berry. It is noteworthy that a similar question is raised with respect to Cyrtandra as to the relation between fleshy fruits in the Pacific islands and dry or capsular fruits in the continental home of the genus (see Chapter XXV.).

The berries of the Tree-Lobelias would attract birds. We learn from Mr. Perkins that one of the Hawaiian Drepanids, the Ou, is very partial to the berries of some of the Tree-Lobelias and especially those of Clermontia, the seeds passing unharmed in the droppings. The mode of dispersal of the seeds of the dry-capsular fruits is not so apparent; but the fruits could scarcely be less inviting to birds than the dry capsules of Metrosideros, the small seeds of which have in some way or other been carried to almost every island-group of the Pacific. I have beside me the dark brown, smooth crustaceous seeds of a species of Clermontia. They measure 1/42 of an inch or 0·6 of a millimetre, and about 500 go to a grain. Mr. Wallace, in his book on Darwinism, advocates the paramount influence of winds over birds for carrying small seeds, like those of Orchis and Sagina, over tracts of ocean a thousand miles across. I am, however, not inclined to think that, except as regards the spores of cryptogams, winds have done very much for Hawaii. For small seeds we can appeal not only to the agency of birds and bats but also to insects (see Chapter XXXIII.).

Observations of this kind, however, merely indicate that these early Lobeliaceæ possessed the same capacities for dispersal that in the succeeding stages of the plant-stocking of the Pacific islands have belonged to Metrosideros, Cyrtandra, Ophiorrhiza, Freycinetia, and many other small-seeded genera. They go no way to explain why the same agencies which transported the minute seeds in a later age could not have been available for continuing the dispersal of the early Lobeliaceæ. To find an explanation we are compelled to go behind the mere capacities for dispersal and to appeal to the general laws of distribution in so far as our facts enable us to interpret them.

We have seen that the two principal components of the early Pacific flora, the Compositæ and the Lobeliaceæ, have American affinities. The plants of the later ages are mainly Old World in their connections. Though containing often endemic species in the various groups, the genera occur also outside each group. The stream of migration that came from America during the early age of the Compositæ and the Lobeliaceæ, when the islands of the Western Pacific were more or less submerged, was during the later ages (after these islands had re-emerged) suspended or diverted, giving place to a stream that brought plants in numbers from tropical Asia, Malaya, and Australia. The general dispersion of the Compositæ and Lobeliaceæ took place during the Tertiary submergence of the islands of the Western Pacific, including the island-groups of Fiji, Samoa, and Tonga. The migration from the west, mainly Indo-Malayan in character, occurred after the re-emergence of those archipelagoes. Thus we get to understand how genera like those of the early Lobeliaceæ and Cyrtandra, which possess, as regards the minute size of their seeds, closely similar capacities for dispersal, have such different distributions, the first confined to Hawaii and Tahiti and American in their affinities, the second widely spread over the Pacific with its home in Malaya.

We have yet to inquire whether this suspension of the means of transport in the later ages of the Pacific Lobeliaceæ is confined to the tropics or whether it extends to the colder latitudes in the southern hemisphere. The indications of the Lobeliaceæ of the “antarctic flora” go to establish that the dispersal of the order is still, or was very recently, in operation in these high latitudes. It is well illustrated, among other plants, by Lobelia anceps, which is found in extra-tropical South America, Australia and New Zealand, and South Africa. This, indeed, recalls Bentham’s view concerning the Compositæ, that whilst communication was broken off in the tropics, it was kept up in higher latitudes.

Here ends, therefore, our consideration of the Tree-Lobelias of the Pacific islands; but as it is not quite complete without a discussion of the remaining endemic genera of other orders than the Compositæ and Lobeliaceæ which also belong to the same early age of the Pacific floras, I will proceed at once to their consideration.

THE HAWAIIAN ENDEMIC GENERA EXCEPTING THOSE OF THE COMPOSITÆ AND LOBELIACEÆ.

It will not be possible for me to do more than point out a few general indications that can legitimately be drawn from these genera. The subject bristles with difficulties for the systematist; but on one point there can be but little danger of going astray, namely, in imputing to them a high antiquity in the floral history of Hawaii. This can be said of all of them, whether or not the generic distinction adopted in Dr. Hillebrand’s work is always adopted by botanists. It is therefore in this general sense that they may be regarded as belonging to the early age of the Hawaiian flora.

Although the genera of Compositæ and Lobeliaceæ are prominent amongst the representatives of the original flora of the Hawaiian Islands, forming about two-fifths of the whole, the genera of other orders are by no means inconspicuous, and their variety is shown in the fact that though twenty-three in number they belong to twelve orders. It is possible to divide these genera into two groups—one the older and perhaps more or less contemporaneous with the Lobeliaceæ and Compositæ, the affinities when apparent being American; the other the more recent and marking the close of the first era of the plant-stocking of these islands, the affinities being all with the Old World, and especially with Malaysia. This grouping is indicated in the list subjoined; and it may be here remarked that whilst shrubs, undershrubs, and perennial herbs of the Caryophyllaceæ, Labiatæ, and Urticaceæ form the features of the earlier group, trees of the Rubiaceæ and Araliaceæ are the most conspicuous members of the later group. At the close of the earliest era known to us of the floral history of the Hawaiian Islands we observe the commencement of those forests that now throughout Polynesia as well as in Hawaii betray their Asiatic origin.

In making this distinction I am proceeding on the assumption that the stream of migration, at first chiefly American in its source, came ultimately in the main from the Asiatic side of the Pacific. The change commenced, as I hold, in the latter portion of the first era of plant-stocking, an era characterised by the arrival of those early plants that are now represented by the endemic genera of the archipelago. The genera of this early period that belong neither to the Compositæ nor to the Lobeliaceæ are, as above observed, arranged by me in two groups, one regarded as contemporaneous with, the other as of later origin than, the genera of these two orders. To the first belong the shrubby, highly differentiated genera of the Caryophyllaceæ, Schiedea and Alsinidendron, and the Labiate genera, similarly differentiated, of Phyllostegia and Stenogyne. To the second belong the Rubiaceous genera Kadua, Gouldia, Bobea, and Straussia, the Araliads Cheirodendron, Pterotropia, and Triplasandra, and the Loganiaceous Labordea.

In the earlier group the fruits are dry in half the genera, and in such cases granivorous birds probably were usually the transporting agents. Only in one case (Nothocestrum) is the fruit a berry, and in the other cases we have fruits like the fleshy nucules of Phyllostegia and Stenogyne which would probably attract birds. In the later group two-thirds or three-fourths of the genera have moist fruits such as would be eaten by frugivorous birds. Of these most are drupes, possessing not a single stone, but two or more pyrenes. This is the first appearance of the drupe in the plant-history of the archipelago. The Rubiaceous type of drupe inclosing two or more pyrenes plays a very conspicuous part in the distribution of plants over the Pacific in the succeeding eras.

I would here lay stress on an important characteristic of all the fruits of the endemic genera of the Hawaiian Islands. There are no “impossible” fruits of this era in Hawaii, such as we occasionally find in the succeeding eras. I mean by this term, fruits that defy the efforts of the student of distribution to explain their transport in their present condition. The discovery of a new inland genus possessing dry indehiscent fruits three or four inches long, or even of a single species of the coniferous Dammara, would play havoc with all our views respecting the stocking of these islands with their plants. The finding here of a large marsupial would scarcely produce more astonishment. The fruits indeed of this early era are very modest in their size, the dry indehiscent fruits and the stone-fruits rarely exceeding half an inch (12 mm.) in size.

There is another interesting point which is connected with the deterioration of some of the fruits in their capacity for dispersal. Some of the species of Phyllostegia, and a few also of the Araliads, as well as those of Nototrichium, are ill fitted for dispersal by birds now, the coverings of the seeds being not sufficiently hard to protect them from injury in a bird’s stomach. At the same time there are in some cases other species of the same genera that are better suited for this mode of transport. The effect of dispersal by frugivorous birds is that only the hard-coated seeds propagate the plant in a new locality. When, however, as has occurred in the Hawaiian Islands, bird-agency largely ceases to act, this selective influence is removed (see Note 68).

ENDEMIC HAWAIIAN GENERA, EXCLUDING THOSE OF THE COMPOSITÆ AND LOBELIACEÆ, AS GIVEN IN HILLEBRAND’S “FLORA OF THE HAWAIIAN ISLANDS.”

[Those preceded by * are not usually regarded now by botanists as endemic, though they nearly take that rank.]

THE EARLIER GROUP.

+-----------------+---------------+---------+------------+-----------------+-----------------------------+ | Genus. | Order. |Number of|Character. | Fruit. | Affinities. | | | | species.| | | | +-----------------+---------------+---------+------------+-----------------+-----------------------------+ |Isodendrion | Violaceæ. | 3 |Shrubs. |Capsule. |American (H). | | | | | | | | |Schiedea |Caryophyllaceæ.| 17 |Undershrubs,|Capsule. {|Near Colobanthus of the | | | | | &c. | {| Antarctic islands, temperate| |Alsinidendron |Caryophyllaceæ.| 1 |Undershrubs.|Capsule, with {| South America, | | | | | | fleshy calyx. {| and Australia (C). | |Platydesma | Rutaceæ. | 4 |Small trees |Capsule. | — | | | | | or shrubs. | | | |Hillebrandia | Begoniaceæ. | 1 |Herbs. |Capsule. | — | |Nothocestrum | Solanaceæ. | 4 |Small trees.|Berry. |South American (H). | |*Haplostachys | Labiatæ. | 3 |Herbs. |Dry nucules. |Regarded by Gray as a | | | | | | | section of Phyllostegia. | |*Phyllostegia | Labiatæ. | 16 |Undershrubs.|Fleshy nucules. {|Belong to the tribe Prasiæ, | | | | | | {| which is mostly Asiatic. | |Stenogyne | Labiatæ. | 17 |Trailers or |Fleshy nucules. {| Two other species of | | | | | climbers. | {| Phyllostegia recorded | | | | | | {| from Tahiti and Paumotu | | | | | | {| Islands. | |Charpentiera | Amarantaceæ | 2 |Trees. |Utricle. |American (H). | |Touchardia | Urticaceæ. | 1 |Shrubs. |Achene with | — | | | | | | fleshy perigone.| | |Neraudia | Urticaceæ. | 2 |Shrubs. |Achene with |Allied to Bœhmeria, a | | | | | | fleshy perigone.| genus of Old and New | | | Worlds. | | THE LATER GROUP. | | | | | | | | |*Pelea | Rutaceæ. | 20 |Trees. |Capsular. |Belongs to Melicope, an | | | | | | | Old World genus (IK). | |Broussaisia | Saxifragaceæ. | 2 |Small trees.|Berry. |Malayan (H). | |*Cheirodendron | Araliaceæ. | 2 |Trees. |Drupe. |Referred to Panax, an | | | | | | | Old World genus (IK). | |*Pterotropia | Araliaceæ. | 3 |Trees. |Drupe. {|Malayan (H). | | | | | | {| Pterotropia referred to | |Triplasandra | Araliaceæ. | 4 |Trees or |Drupe. {| Heptapleurum of Old | | | | | shrubs. | {| World (IK). | |Kadua | Rubiaceæ. | 16 |Shrubs, &c. |Capsular |Approaches both Asiatic | | | | | | | and American types (C). | |Gouldia | Rubiaceæ. | 5 |Small trees |Drupaceous |American (C). | | | | | or shrubs. | berry. | | |*Bobea | Rubiaceæ. | 5 |Small trees.|Drupe. |Malayan (H). Genus | | | | | | | also in Malaya (IK). | |Straussia | Rubiaceæ. | 5 |Trees. |Drupe. |Near Psychotria, a genus | | | | | | | of Asia and America (H). | |Labordea | Loganiaceæ. | 9 |Small trees |Capsule with |Malayan (H). | | | | | or shrubs. | pulp. | | |*Nototrichium | Amarantaceæ. | 3 |Trees or |Utricle. |Referred to the Australian | | | | | shrubs. | | Ptilotus (IK). | +-----------------+---------------+---------+------------+-----------------+-----------------------------+

(H) = Hillebrand’s _Flora of the Hawaiian Islands_. (C) = Drake del Castillo’s _Remarques sur la Flore de la Polynésie_. (IK) = _Index Kewensis._

NOTE.—Probably Schumann’s genus, Pteralyxia, should be placed in the later group (see p. 154).

Another feature of interest is to be found in the distribution within the archipelago of the species of the peculiar genera. As in the case of the Compositæ and Lobeliaceæ, but few of the species are generally distributed, most being restricted to one island or to two or three adjacent islands. The suspension of the dispersal among the islands is, however, not so marked as with the species of the two orders just named.

NOTE.—Some further remarks on some of these genera are given in Note 68.

THE ENDEMIC GENERA OF THE FIJIAN ISLANDS.

The interest that is associated with the endemic genera of Hawaii fails to attach itself to those of Fiji. For this there are several reasons. In the first place, our acquaintance with the Fijian flora is much less complete. In the next place, the group holds a much less isolated position, and the history of an endemic genus may have a significance quite different from that connected with it in Hawaii. Fiji also lacks, on account of its submergence in the Tertiary period, those highly interesting genera of the Compositæ and Lobeliaceæ that form the chief feature in the early history of the flowering plants of Hawaii. Then, again, on account of our imperfect knowledge of the floras of the neighbouring groups of continental islands to the westward, the New Hebrides, Santa Cruz, and Solomon Groups, we can never feel quite confident that any particular genus is really peculiar to the Fijian archipelago. This is well brought out in the later history of the genera designated by Dr. Seemann in his _Flora Vitiensis_ as peculiar to Fiji.

Of the sixteen genera enumerated by Dr. Seemann, and given in the table below, only about half now retain their character of being restricted to Fiji. Nor does it seem likely that future investigations will increase this number, since, judging from a remark made by Mr. Hemsley in his paper on the botany of the Tongan Group, explorations subsequent to those of Dr. Seemann, more especially those of Mr. Horne, have not apparently added a single new endemic genus to the Fijian flora. It will be seen from the list that at least four of the sixteen genera have since been found in the Malayan region, and in one case (Smythea pacifica) the same species occurs in both regions; whilst a fifth genus (Haplopetalon) has been recorded from New Caledonia.

There are, however, some peculiarities about the Fijian endemic genera that will attract our attention from the standpoint of dispersal. One remarkable feature is the paucity of species. Almost all the genera are monotypic, that is to say, they are only known by a single species. Amongst the twenty-eight Hawaiian genera that are strictly endemic, only four or five are monotypic, and they are mostly regarded by Hillebrand as worn-out, decadent types found in only one or two islands. In Hawaii there are on the average six species to each endemic genus; and it is thus apparent that in the display of formative energy Nature has worked on very different lines in these two groups. Since the nine Fijian endemic genera belong to nearly as many different orders, the composition of this endemic generic flora is by no means homogeneous. It is, I venture to think, such a motley collection as one might expect in a region that has been exposed to wave after wave of migration from the west, with no lofty mountains, as in Hawaii, to afford a refuge against extinction. It by no means follows that all these endemic genera have been produced in Fiji. Some of them may represent genera that have become extinct in the large continental groups to the westward.

SEEMANN’S SIXTEEN FIJIAN ENDEMIC GENERA.

Those genera marked * have since been found outside the group.

The authorities are thus indicated: (C)=Drake del Castillo; (H)=Horne; (IK)=_Index Kewensis_ (S)=Seemann; (Sc)=Schimper; (So)=Solereder in Engler’s _Nat. Pflanz. Fam._

The fact that several of them are fitted for dispersal by frugivorous birds is very suggestive of the lack of means of transport in later times. In the instance of Couthovia corynocarpa the drupes are known to be the food of fruit-pigeons at the present time (Seemann), whilst this is also true of Oncocarpus vitiensis, though this genus has since been found in New Guinea. Since, as will be pointed out in a later chapter, birds must still be fairly active in carrying seeds to Fiji from regions westward, it would seem that genera only become peculiar to Fiji when they fail at their source, and it is indeed doubtful whether any of the Fijian peculiar genera are home productions. One may instance in this connection the genus Pimia, the fruits of which are especially well suited for attachment to a bird’s plumage, yet it is only known from Fiji.

It should be here observed that no peculiar generic types have been recorded from the adjacent Tongan Group, and scarcely any from Samoa. Except perhaps with the Palmaceæ, no peculiar genera seem to be mentioned in Dr. Reinecke’s memoir on Samoa.

_Summary._

(1) The Lobeliaceæ, like the Compositæ, take a prominent place in the early Pacific flora, being represented, more particularly in Hawaii but also in the East Polynesian or Tahitian region, by endemic genera of tall shrubby and tree-like species.

(2) Tree-Lobelias occur in other parts of the world, as in South America and tropical Africa; but it is especially on the higher slopes of the mountains of Equatorial Africa that they attain a development comparable with that of Hawaii.

(3) In Hawaii the Tree-Lobelias are most characteristic of the middle forest-zone (3,000-6,000 feet), where the temperature is mild, the rainfall heavy, and the atmosphere laden with humidity.

(4) The affinities of these endemic genera of the Lobeliaceæ are mainly American; but their generic distinctions have been both exaggerated and disguised by redundant growth.

(5) From the distribution of the genera and species within the Hawaiian Group it is evident that, as with the early Compositæ, the original Lobeliaceous immigrants were not all contemporaneous arrivals. Some of the genera are on the point of extinction, whilst others are in their prime.

(6) The absence of the Lobeliaceæ from the groups of the Fijian area (Fiji, Tonga, Samoa) is probably to be connected, as in the case of the absence of the early Compositæ, with the circumstance that the general distribution of these two orders over the tropical Pacific occurred during the Tertiary submergence of these archipelagoes.

(7) These endemic genera of the Lobeliaceæ possess the same facilities for dispersal that are owned by other genera with minute seeds, such as Cyrtandra, &c., that are dispersed over the Pacific; but in the case of the Lobeliaceæ the agencies of dispersal have been for ages suspended.

(8) This suspension is to be associated with the diverting of the main stream of migration from its source in America, during the early age of the Lobeliaceæ and Compositæ, to a source on the Asiatic side of the Pacific.

(9) The Hawaiian endemic genera other than those of the Compositæ and Lobeliaceæ arrange themselves in two groups—an earlier group containing highly differentiated Caryophyllaceæ and Labiatæ, and belonging to the age of the Compositæ and Lobeliaceæ; and a later group, characterised by Rubiaceæ and Araliaceæ, which marks the close of the first era, as well as the change in the main source of the plants from America to the Old World, the beginning of the Hawaiian forests, the appearance of the Rubiaceous drupe, and the first active intervention of frugivorous birds.

(10) Though there are no “difficult” or “impossible” fruits (fruits, the dispersal of which is not easy to explain) amongst the forty and odd endemic genera of Hawaii and Tahiti, it is noteworthy that in some cases the fruits are seemingly little fitted for dispersal now, and that this deterioration in capacity for dispersal is to be frequently associated with more or less failure of the inter-island dispersal in the case of Hawaii.

(11) The interest associated with the Hawaiian endemic genera fails to attach itself to those of Fiji, where genera only seem to have become peculiar because they have failed at their sources in the regions to the west. The endemic genera of the Compositæ and Lobeliaceæ are here lacking, and this is true also of the neighbouring Samoan and Tongan Groups, it being held that the age of the general dispersion of these orders over the Pacific corresponded with the Tertiary submergence of the archipelagoes of the Western Pacific. Those of Fiji, which do not amount to ten in number, belong to nearly as many orders and present a motley collection such as one might look for in a group much less isolated than Hawaii and exposed to wave after wave of migration from the west.