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.
| Genus. | No. of species. | Distribution of genus. | Distribution in the group. | Height of plant. | Nature of Station. | |
|---|---|---|---|---|---|---|
| Elevation. | Station. | |||||
| Brighamia | 1 | Endemic. | Molokai, Niihau. | 5 to 12 feet. | Islands not exceeding 3,500 feet. | Steep palis or mountain gaps. |
| Lobelia | 5 | Non-endemic. | General. | 4 to 6 feet. | 2,000 to 6,000 feet. | Bridges, gulches and woods. |
| Clermontia | 11 | Endemic. | General. | Usually 10 to 20 feet.[[2]] | 2,000 to 6,000 feet. | Open woods. |
| Rollandia | 6 | Endemic. | Oahu. | Usually 4 to 6 feet, one species 10 to 15 feet. | Higher parts of Oahu, which is 4,000 feet high. | Woods. |
| Delissea | 7 | Endemic. | General. | 5 to 10 feet. | 1,000 to 5,000 feet. | Woods and gulches. |
| Cyanea | 28 | Endemic. | General. | Usually 6 to 15 feet.[[3]] | 1,000 to 5,000 feet. | Woods, ravines, gulches. |
| East Polynesian or Tahitian Islands. | ||||||
| Sclerotheca | 4 | Endemic in E. Polynesia. | Tahiti, Rarotonga. | 6 to 25 feet. | 1,500 to 3,000 feet. | Humid wooded slopes. |
| Apetahia. | 1 | Endemic. | Raiatea. | 3 to 6 feet. | In the mountains. Elevation of island 3,400 feet. | |
[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.
[2]. The range of the heights of different species of Clermontia is from 5 or 6 feet for shrubs to 25 feet for trees.
[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.