CHAPTER XXVII

THE MALAYAN ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (_continued_)

THE AGE OF LOCAL DISPERSAL

_Synopsis of the Chapter._

HAWAII.—(1) _The Hawaiian residual genera, being those not found in either the Fijian or the Tahitian regions._ The genera especially discussed are Osmanthus, Sicyos, Jacquemontia, Cuscuta, Rumex, Dracæna, Naias, Potamogeton; and amongst others mentioned are Perrottetia and Embelia.

(2) _The Hawaiian genera found in Tahiti and not in Fiji._ Very few, and illustrated by Byronia, Reynoldsia or Trevesia, Phyllostegia, and Pseudomorus, though it is likely that most of these will be subsequently discovered in Fiji.

(3) _The Hawaiian genera found in Fiji and not in Tahiti._ Illustrated by Eurya, Gouania, Maba, Sideroxylon, Antidesma, Pleiosmilax, Ruppia.

(4) _The absentees from Hawaii._ Illustrated amongst the orders by the Sterculiaceæ (see text), the Meliaceæ, the Rhizophoreæ, the Melastomaceæ, and the Coniferæ, and amongst the genera by Trichospermum Loranthus, Stylocoryne, Ophiorrhiza, Alstonia, Hoya, Ficus; and a great many others might be cited.

TAHITI.—(1) _The Tahitian residual genera._ Only six in number—Cratæva, Buettneria, Berrya, Coriaria, Bidens, Lepinia.

(2) _The Tahitian genera found in Hawaii and not in Fiji._ See above under (2).

(3) _The Tahitian genera found in Fiji and not in Hawaii._ (a) Those possessing only species confined to the Tahitian region or to East Polynesia, of which Meryta, Ophiorrhiza, Alstonia, and Loranthus are examples.

(b) Those possessing widely-ranging species besides, often, species confined to the Tahitian region, such as Grewia, Nelitris, Melastoma, Randia Geniostoma, Tabernæmontana, Fagræa, Bischoffia, Macaranga, and Ficus. The widely-ranging species is in many genera polymorphous.

(4) _The absentees from Tahiti._ Amongst the orders are the Meliaceæ, the Rhizophoreæ, and the Coniferæ. Amongst the genera, usually those with “stones” or large seeds an inch in size, such as Canarium, Dracontomelon, Myristica, Sterculia, Veitchia, &c. Numerous other absent genera might be named.

FIJI.—_The Fijian genera not found either in Tahiti or Hawaii._ These genera compose about half the Fijian flora, being at least 160 in number. Those especially discussed here are the following:—Hibbertia, Cananga, Sterculia, Trichospermum, Micromelum, Canarium, Dracontomelon, Begonia, Geissois, Dolicholobium, Lindenia, Myrmecodia, Hydnophytum, Couthovia, Limnanthemum, Myristica, Elatostema, Ceratophyllum, Gnetum, Veitchia, Rhaphidophora, Lemna, Wolffia, Scirpodendron. The Coniferæ are dealt with in Chapter XXIV.

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Note appended on Marsilea

HAVING completed our discussion of the general dispersal of tropical genera, chiefly Indo-Malayan, over the Pacific islands, we pass on now to consider the more restricted distribution of non-endemic genera over this region. Here as before we take Hawaii, Tahiti, and Fiji as the three centres of distribution; and here also we deal with the flowering plants after excluding the orchids, the sedges, the grasses, the mountain-plants, and all plants introduced either by the aborigines or by white men.

HAWAII.

After excluding the endemic genera as well as those that are confined to the mountains, we find that this group possesses very few genera that do not occur in the Fijian and Tahitian regions, and fewer still that it owns in common with Tahiti to the exclusion of Fiji. On the other hand, we observe that Fiji possesses a great number of genera, mostly Asiatic in origin, that have not reached Hawaii, and in several cases are not known, from the Tahitian region. These contrasts might have been expected, since the Pacific islands have in later ages been mainly stocked from the Asiatic side of the Pacific, the principal route lying through the Fijian region.

As far as the flora of the lower levels (below 4,000 feet) is concerned, Hawaii only possesses a portion of that which Fiji has derived from the Old World, chiefly through Malaya. Although, as will be shown below, there is a noticeable contribution from America, it is very far from counterbalancing the loss which the Hawaiian flora has sustained in comparison with Fiji through the isolated position of the group. The want of variety, however, in the flora of the Hawaiian lower levels, which up to 4,000 or 5,000 feet represent the islands of the less elevated Fijian region, is in a small degree compensated for by the development of new genera and new species and by the great number of individuals. Trees like Metrosideros polymorpha and Aleurites moluccana, that in the southern groups form only one of many contributors to the forests, rise suddenly into prominence in the northern archipelago and form entire forests. Pandanus odoratissimus largely composes extensive forests in the province of Puna in the large island of Hawaii, extending several miles inland and nearly 2,000 feet up the mountain slopes.

The remarkable contrast between the Fijian flora, which is almost entirely tropical, and the Hawaiian flora, which on account of the great elevation of the islands is temperate as well as tropical, is brought into yet greater prominence when we look at it more closely and treat it numerically. The Hawaiian Group, it must be first observed, though possessing the same area as Fiji and presenting a far greater variety of climatic conditions, has only two-thirds the number of genera of flowering plants (see Chapter XXI., Table B). Whilst at least 200 of the Fijian genera of indigenous plants (excluding the orchids and the grasses) are not found in Hawaii, only about 100 of the Hawaiian genera are absent from Fiji, and the two groups possess about 100 genera in common. When we look more closely at the hundred Hawaiian genera not found in Fiji, we find that about sixty represent endemic genera (thirty-seven) and non-endemic mountain-genera (twenty-two), which naturally are not to be found in Fiji, so that there remain but a small number of genera distinguishing the tropical flora of Hawaii from the Fijian flora. When we take from them a few that occur in the Tahitian region, there is left a very small residuum characteristic of Hawaii alone to the exclusion of the Fijian and Tahitian regions of the South Pacific.

THE HAWAIIAN RESIDUAL GENERA.

It is my purpose now to deal in an illustrative fashion with this Hawaiian residual flora which is composed, as above explained, of the non-endemic tropical genera that are not represented in the Fijian and Tahitian regions. Up to the present we have been dealing with the characters that the floras of Fiji, Tahiti, and Hawaii possess in common as far as tropical genera are concerned. We will now proceed to discuss their differences in this respect, and will begin with the residual Hawaiian flora.

After eliminating two or three genera that will probably be found in Fiji, but including one or two others that are best treated under the endemic genera, about twenty-seven present themselves for our purpose. Nearly all of them possess only endemic species, and belong therefore to an age of dispersal that has passed away. These residual genera plainly indicate that although Hawaii largely received its flora during the age of general dispersal of Old World genera over the Pacific, it was at the same time independently stocked with plants from other sources. They include among others—Cocculus (4), Cleome (1), _Perrottetia_ (1), Mezoneuron (1), _Lythrum_, _Sicyos_ (8), Peucedanum (2), Campylotheca (12), Senecio (2), Lobelia (5), Embelia (1), _Chrysophyllum_ (1), Rauwolfia (1), _Nama_ (1), Osmanthus (1), _Jacquemontia_ (1), Breweria (1), Cuscuta (1), Lycium (1), _Sphacele_ (1), _Phytolacca_, Rumex (2), _Urera_ (2), Pilea, Dracæna (1), Naias, Potamogeton. Those printed in italics are regarded as derived from America; whilst the figures in brackets indicate the number of endemic species, nearly all of the genera except the five above indicated possessing only peculiar species, and these five (Lythrum, Phytolacca, Pilea, Naias, Potamogeton) are only represented by species found outside the group.

American genera form a more conspicuous element than they do amongst the genera that have been generally dispersed over the Pacific, those exclusively American being fairly represented, making a third of the whole. We find, for instance, in the Hawaiian “Olomea,” Perrottetia sandwicensis, a small tree that represents in the woods of all the islands the Perrottetias of Mexico and the Andes; whilst with some of those genera that, like Sicyos and Urera, are at home in both the Old and New Worlds, we obtain indications of America being the source of the Hawaiian plants. A few genera again, like Lythrum and Phytolacca, are represented in Hawaii by American species.

Plants with drupes, berries, or other fleshy fruits likely to attract frugivorous birds compose about a third of the total number of these residual genera, whilst fruits or seeds, that were in all probability originally brought entangled in a bird’s feathers, are represented by Sicyos. Some of the genera with stone fruits, such as Osmanthus, to which belongs the Hawaiian Olive, present special difficulties on account of the size of the stone, in this case two-thirds of an inch in length. There are also a number of genera with large dry fruits and sometimes large seeds, of which the method of dispersal is not easy to discover. Thus, Mezoneuron, a Leguminous genus with seeds an inch across (2·5 cm.), and Peucedanum, of the Umbelliferæ, with mericarps half to three-quarters of an inch (1·2 to 1·8 cm.) in length, offer serious difficulties to the student of plant-dispersal. In discussing the difficulty connected with Mezoneuron (see Chapter XV.) he will keep in view the possibility that the original species may have been a littoral plant possessing seeds dispersed by the currents, seeds that lost their buoyancy when the plant established itself inland, just as is now taking place with Afzelia bijuga, a Leguminous littoral tree of Fiji (see