The Mountain-Flora of the Tahitian Region as Illustrated by the Non-Endemic Genera

This floral region of the Pacific corresponds with the limits of Eastern Polynesia, and includes not only the Tahitian group proper, but also the Cook, Austral, Paumotuan, and Marquesan groups. It is only, however, in Tahiti, the peaks of which rise to over 7,000 feet above the sea, that we should expect to find such a mountain-flora, since the islands of the other groups are much lower, the highest of them in the Marquesan group barely exceeding 4,000 feet. Yet even in Tahiti it is not possible to speak of a mountain-flora in the sense that we attach to it in Hawaii. The elevated area of its interior is, as described in [Chapter XIX.], relatively very small; whilst, as Drake del Castillo points out, the conditions presented by the steep mountain-slopes rarely afford a hold for trees of any size, ferns often predominating in the higher levels. Still, we can observe the traces of such a flora, and it is in this sense only that the term “mountain-genera” is used in relation with this group.

Mountain-Genera of the Tahitian or East Polynesian Region.

all species endemic.

some species endemic

The Tahitian non-endemic mountain-genera, though scanty in number, are of considerable interest to the student of plant-dispersal. Among those possessing only species that are confined to Eastern Polynesia, genera that would be regarded as belonging to a past era of dispersal, Weinmannia, Coprosma, Vaccinium, and Astelia may be mentioned.

Weinmannia, a Saxifragaceous genus of trees and shrubs, not represented in Hawaii, but recorded from almost all the elevated oceanic groups of the tropical South Pacific, as well as from the New Hebrides and New Caledonia, has its home in South America, more particularly in the Andes, and also occurs in New Zealand, Tasmania, and the Mascarene Islands. One can scarcely doubt that, as in the case of Coprosma, the Pacific Islands derived their species originally from high southern latitudes, as from New Zealand, the absence of the genus from Hawaii negativing an American origin. Of the two Tahitian species, one is peculiar to Tahiti, whilst the other, W. parviflora, which is conspicuous on the mountain-crests at elevations of 3,000 feet and over, occurs also in the Marquesas. Another species grows in abundance in the interior of Rarotonga. Samoa possesses two species, one of which, W. affinis, occurs in Fiji, and the other, W. samoensis, which frequents the mountains at elevations of 1,500 to 3,300 feet, is seemingly endemic. Fiji possesses four or five species of Weinmannia occurring at all altitudes up to 2,000 feet, of which some are evidently peculiar. The capsular fruits of this genus contain hairy seeds that would probably become entangled in a bird’s plumage. Dispersal by birds is distinctedly indicated in the curious observation of Dr. Reinecke in the case of the Samoan peculiar species. The seeds, he says, appear to germinate by preference on the bark of other trees, young plants growing epiphytically being of frequent occurrence.

There is some evidence that the species of Weinmannia, about ten in all, found in the tropical islands of the open Pacific are derived from one or two polymorphous species. As we learn from Mr. Cheeseman, the Rarotongan species, W. rarotongensis, has considerable affinity to several closely allied Polynesian species, and its nearest allies are a Fijian and Samoan species, W. vitiensis and W. samoensis. Possibly, he remarks, fuller materials may lead to the union of several of these forms under one species.

The interesting New Zealand genus Coprosma, which we have noticed in Hawaii, occurs also in the Tahitian region and Fiji; and it will be further discussed under the last-named locality. The genus Vaccinium has been previously dealt with in [Chapter XXIII.]

The Liliaceous genus Astelia may be considered as representing, like Coprosma, the Antarctic or New Zealand flora in the higher levels (usually) of the islands of the tropical Pacific, where it grows both on trees and on the ground. The genus, according to Hemsley, is chiefly at home in New Zealand, but is also found in Fuegia and in South-east Australia. It is represented in Hawaii, Tahiti, Samoa, and Fiji. In Hawaii there are two peculiar species ranging between 2,000 to 6,000 feet in elevation. The solitary Tahitian species, A. nadeaudi, is found in the central mountains of Tahiti, reaching to the crests of Mount Aorai, which attains a height of 6,700 feet. Fiji and Samoa possess a species in common, A. montana, which is only recorded by Seemann, from the summit of Kandavu, 2,750 feet above the sea; whilst in Samoa it frequents, according to Reinecke, moist coast districts. The fruits of Astelia are berries with crustaceous seeds that would be dispersed by frugivorous birds.

Amongst the Tahitian mountain-genera that possess species ranging far beyond this region as well as species confined to the group may be mentioned Coriaria and Cyathodes. It is to their non-endemic species that we look for further clues as to the general lines of migration by which the mountain-genera that only possess peculiar species reached this group. The evidence afforded by Coriaria is of some importance. The genus has not been recorded from Hawaii, and, so far as the collections of Seemann and Home show, not from Fiji. It is found in the Mediterranean region, the Himalayas, Japan, New Zealand, and Antarctic America, including Chile; and there are two particular species, C. ruscifolia and C. thymifolia, that occur in both cases in New Zealand and the adjacent islands and in South America (Introd. Chall. Bot. p. 53). The first of these, which is very common in Chile, exists also in Tahiti on the crest of Aorai, 6,700 feet above the sea. Drake del Castillo also describes a peculiar Tahitian species, C. vescoi, of which the altitude is not given. Here one is in doubt whether Tahiti derived its wide-ranging species from New Zealand or from Chile; but in the New Zealand home of Coprosma, another Tahitian mountain-genus, we are afforded the clue. The fruits of Coriaria possess fleshy cocci that attract birds, though it would seem that the seeds of plants of this genus are poisonous for man. Among the numerous fruits that form the diet of the New Zealand fruit-pigeon (Carpophaga novæ zealandiæ) are included, as we learn from Sir W. Buller in his Birds of New Zealand, those of the “tupakihi” or “tutu” shrub, which Kirk identifies with C. ruscifolia, the species that also occurs on the summit of Tahiti.

The Australian and New Zealand genus Cyathodes (Epacridaceæ) has been already noticed in the case of Hawaii (page [282]). The two Tahitian species occur on the elevated mountain-ridges forming the summits of Tahiti, one of them, C. tameiameiæ, occurring also in Hawaii, and the other, C. pomaræ, being restricted to the group. I have shown that the fruits are dispersed by frugivorous birds, and I can only include the genus as another example of the representation of the New Zealand flora in Tahiti.... There remain of these so-called Tahitian mountain-genera the Antarctic Nertera and the north-temperate Luzula, each represented by a solitary widely ranging species, N. depressa and L. campestris, which I have fully discussed under Hawaii ([Chapter XXIII]), in which group they also occur.

When we look at the evidence of origin supplied by the four Tahitian mountain-genera possessing species that are found outside the group, namely Coriaria, Cyathodes, Nertera, and Luzula, we find that the first three hail from high southern latitudes, and more especially from New Zealand; and when with this clue in our hands we take up the four genera Weinmannia, Coprosma, Vaccinium, and Astelia, possessing only species restricted to the Tahitian region, we find that all but the third-named genus hail also from the south. It would thus appear that the element of the Antarctic flora is much more evident in the Tahitian mountain-genera than with those of Hawaii. In the Hawaiian mountain-flora, excluding, of course, the endemic genera, it includes about a fourth of the mountain-genera, which number about thirty-eight or forty in all; whilst in the Tahitian mountain-flora it comprises six out of the eight genera. It may, indeed, be said that the resemblance between the mountain-genera of Hawaii and Tahiti is mainly restricted to genera that are found in high southern latitudes, namely, Nertera, Coprosma, Cyathodes, and Astelia, the only other genera linking the mountain-floras of both groups together being Vaccinium and Luzula, which probably hail from high northern latitudes. The agency of the frugivorous bird is plainly marked in the case of five out of the six genera that connect the cloud-capped peaks of Tahiti and Hawaii. In two of these genera, Cyathodes and Nertera, the same species occurs in both archipelagoes.

The Mountain-flora of Rarotonga.—A word may here be said on the representation of these mountain-genera in Rarotonga, a small island 2,250 feet in height and about eight miles in length, which is, however, the most important island of the Cook group. The recent important explorations of Mr. Cheeseman show that its flora is essentially Tahitian in character. As in Tahiti, the early age of the Compositæ and Lobeliaceæ is well represented in the high levels by peculiar species of Fitchia and Sclerotheca which are discussed in Chapters [XXI] and [XXII]. On account, however, of its relatively low altitude and its small size, we could not expect any extensive representation of the eight non-endemic mountain-genera of Tahiti. Yet three of these occur, a Tahitian species of Vaccinium (page [281]) growing on its summits, whilst peculiar species of Weinmannia (page [290]) and Coprosma (page [295]) are found in its interior. The prevailing condition of many of the genera growing in the higher levels is one of isolation, since other genera, like Pittosporum and Elæocarpus, only possess peculiar species; but seeing that in several cases the species are closely allied to others found in the Western Pacific, as in Samoa, Fiji, and the Kermadec group, it is apparent that the period of isolation has not long commenced.

The Mountain-Flora of the Fijian Region.

Derived from New Zealand or from the Antarctic flora.

Not as a rule belonging to the present age of dispersal

But little can be said of the mountain-flora of Fiji, since on account of the relatively low elevation of the islands there are but few special mountain-genera; and as a rule we find only here and there a solitary species on some isolated peak that recalls the upland flora of the Hawaiian mountains. “None of the mountains of Fiji,” remarks Horne (page [60]), “are high enough for an alpine flora to exist. Many of the plants found on the tops of the mountains are also found near the level of the sea. On the other hand sea-level plants may also be found on the tops of the hills.”

Fiji lacks the endemic genera of Compositæ and of Lobeliaceæ that often give a character to the mountain-floras of the Hawaiian and Tahitian regions, though, as remarked in Chapters [XXI] and [XXII.], their absence involves something more than a question of station. We find, however, four genera of the Antarctic or New Zealand flora, Weinmannia, Lagenophora, Coprosma, and Astelia. The first-named genus possesses four or five species ranging up to 2,000 feet, some of which are endemic, and it has been already discussed in this chapter. The United States Exploring Expedition found a single species of Lagenophora (L. pickeringii) on the mountains of the Mathuata coast of Vanua Levu, and no other species seems to have since been found. The subject is dealt with in [Chapter XXIII] in the case of Hawaii, but it may be here observed that there is an Hawaiian mountain species, and that the route followed by the ancestor of the Fijian species from the New Zealand home of the genus is indicated by a species in the intermediate Kermadec group. The genus Astelia has been discussed on page [291]. It is represented in Hawaii and in most of the oceanic groups of elevated islands. The solitary species, A. montana, discovered by Seemann on the summit of Kandavu in Fiji, has since been found in Samoa, and probably Mr. Horne’s collections contain another species.

The Rubiaceous genus Coprosma needs a few special remarks, since a particular genus of birds seems to have been concerned in dispersing it in the South Pacific. About fifty species are enumerated in the Index Kewensis, and if we include a few other species from the collections of Hillebrand, Horne, Cheeseman, &c., the total would be about sixty. Of these, about half are restricted to New Zealand, which may be justly regarded as the home of the genus, the rest being confined to Australia and the islands of the Pacific, excepting a Chilian and three or four Malayan species. Hawaii with its nine species, Tahiti with two, Rarotonga with one, and Fiji with two or three species represent approximately the distribution of the genus in the oceanic archipelagoes of the tropical Pacific. (It most probably exists on the high peaks of Samoa, though it has not yet been recorded from the group.) In all, or in almost all cases, the species are restricted to their particular groups, so that we may regard the dispersal of the genus over the Pacific as suspended, though, as will be observed below, the period of suspension in the South Pacific has not been of sufficient duration to obliterate the affinities of species in distant groups and to prevent us from tracing out the route followed by the genus.

This genus of temperate latitudes, which in its New Zealand home ranges from near the sea-level to the region of the alpine floras, finds its usual station in the tropics on the summits of mountains. Thus, on Mount Kinabalu, in Borneo, it is found at altitudes of 10,500 to 13,000 feet (Stapf), and on the mountains of East Java at elevations exceeding 9,000 feet (Schimper). In Hawaii its species grow at elevations ranging from 3,000 to 9,000 feet, and in Tahiti at altitudes of 2,600 to 3,300 feet; whilst in Rarotonga it grows in the hilly parts of the island, its elevation in Fiji not being recorded.

When we come to consider the route by which the genus (Coprosma) entered the tropical Pacific, we must remember that unless we establish some special connection with its New Zealand home it will always be open for any one to suggest that the genus might have been derived, like Vaccinium, from other regions than the south, as from the summits of the Malayan mountains. However, a curious connection has been discovered by Mr. Cheeseman in his examination of the Kermadec and Rarotongan floras, and it would indeed appear that he has traced the Rarotongan peculiar species to its New Zealand home. Thus, he says that Coprosma lævigata, his new Rarotongan species, is very closely allied to the Kermadec endemic plant, C. acutifolia, Hook., which itself comes near C. lucida, Forst., a New Zealand species. The connection between Rarotonga and New Zealand by way of the Kermadec group is rendered yet more probable by the occurrence of two New Zealand species of Coprosma in the Kermadec flora (Journ. Linn. Soc. i. 1857; Trans. Linn. Soc. Bot. vi. 1903; Trans. N.Z. Instit. xx. 1887).

When speaking of the genus in Hawaii (page [275]), mention was made of the inter-island dispersal of the fruits of one of the species by the native mountain-goose, Bernicla sandwicensis. We learn from Sir W. Buller’s History of the Birds of New Zealand that when the Coprosma is in fruit the Swamp-Hens (Porphyrio melanotus) come out to feed on it. These birds, he says, are capable of prolonged flight; and I chance to have beside me a cutting from the Field of July 9, 1904, in which “Hy. S.” refers to a Black-backed Porphyrio that was captured in 1876 four hundred miles off the coast of New Zealand. This genus, which is widely dispersed in the tropics, the birds being commonly known as Sultanas, Blue Gallinules, Purple Water-Hens, &c., has probably been a very important factor in the dispersal of plants, especially in connection with insular floras. The birds live on a variety of food. The Messrs. Layard observed that Porphyrio vitiensis, which abounds in the swamps of New Caledonia, fed on maize, yams, &c. (Ibis, 1882); whilst in the stomach of a bird of the same genus shot in the Rewa swamps in Fiji I found a number of the stony fruits of Scleria, a genus of the Cyperaceæ. According to Mr. Wiglesworth, each region in the South Pacific has its own species of Porphyrio. There is one in the Tahitian Islands, and another common to Fiji, Tonga, and Samoa; whilst New Caledonia and the New Hebrides have their species (“Aves Polynesiæ”). However, it is evident that the power of dispersing seeds from group to group is not quite suspended, since, as we learn from Sir W. Buller, the New Zealand species, above named as partial to Coprosma drupes, is distributed over Tasmania and Australia, and reaches also Niue and New Caledonia; whilst the Messrs. Layard evidently regarded one species as common to Fiji and New Caledonia.

It is doubtless to birds of this description that we owe some of the specific connections of Coprosma between groups of the Western Pacific. That the dispersal of the species over distant regions was recently in active operation is shown by the close affinity, according to Dr. Stapf, of two species growing on the summit of Kinabalu, the Bornean mountain, with certain species from New Zealand and South-east Australia. Other Rubiaceous species, like Nertera depressa, possessing Coprosma-like fruits and fitted for the same mode of dispersal, link the heights of Kinabalu with the flora of high southern latitudes.

Being included in the Fijian area, the scanty mountain-flora of Samoa may be here referred to. As in Fiji, the endemic genera of Compositæ and Lobeliaceæ are not to be found, but we find in the central elevated district of Savaii, which rises to over 5,000 feet above the sea, a peculiar species of Vaccinium (4,900 feet), the Antarctic Nertera depressa (4,000 feet), and two species of Weinmannia, a genus hailing probably from high southern latitudes.