| Hawaiian Lobeliaceæ. | Brighamia. | Lobelia. | Clermontia. |
|---|---|---|---|
| Species confined to one island | — | — | 6 |
| Species confined to two islands | 1 | 2 | 2 |
| Species confined to three islands | — | 1 | 2 |
| Species generally distributed, but still endemic | — | 2 | 1 |
| 1 | 5 | 11 |
| Hawaiian Lobeliaceæ. | Rollandia. | Delissea. | Cyanea. | Total. |
|---|---|---|---|---|
| Species confined to one island | 6 | 4 | 22 | 38 |
| Species confined to two islands | — | 2 | 5 | 12 |
| Species confined to three islands | — | 1 | 1 | 5 |
| Species generally distributed, but still endemic | — | — | — | 3 |
| 6 | 7 | 28 | 58 |
[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.