The Endemic Genera of Compositæ.

On account of their endemic character the peculiar genera of Compositæ are regarded as belonging to the oldest era of the flowering plants of the island-groups lying in the tropical latitudes of the open Pacific. This is the view of Bentham, but it is, of course, the opinion that most botanists would arrive at with the facts before them. With the exception of the solitary Tahitian genus Fitchia, they are all restricted to the Hawaiian Islands, and nearly all are either shrubby or arborescent, the greatest height of 25 to 30 feet being attained in the Tahitian genus and in Hesperomannia of Hawaii.

Nine Hawaiian genera are included in this era, though, strictly speaking, we ought only to concern ourselves with the six genera, Remya, Argyroxiphium, Wilkesia, Dubautia, Raillardia, and Hesperomannia, since the other three, Tetramolopium, Lipochæta, and Campylotheca, are only on the borderland of generic distinction. It is, however, necessary that we should include these three genera in our treatment of the Hawaiian endemic genera, more especially because they appear to have been the last arrivals of the early Compositæ. They still display, as shown below, a very suggestive connection with the land of their birth, a circumstance that is of much importance in finally determining the source of the other strictly endemic genera, where the links with their original homes have been in most cases largely severed.

It would, however, be quite out of place here to enter into any details into the affinities of these Hawaiian genera of Compositæ, and I will limit myself here to such general conclusions as may be derived from the pages of Bentham, Hillebrand, Hemsley, and other writers, and such as are in accordance with the facts of distribution given in the Index Kewensis. Most ancient of all are the genera Remya, Argyroxiphium, Wilkesia, and Hesperomannia, which, although belonging to tribes that only occur on the American continent, as in the Mexican region, stand quite isolated, and, as Dr. Hillebrand remarks, probably belong to the oldest denizens of the Hawaiian Islands. It is noteworthy that these four ancient genera only contain two species apiece, a circumstance that favours their priority in point of age.

The American affinities, however, are not always of the character that we might have expected. Thus, it was remarked by Mr. Bentham that although the tribe Mutisiaceæ attains a great development in South America, and especially in Chile, its only representative in the Pacific islands is the very rare arboreous Hesperomannia of Hawaii.

Rather less isolated in character, and we would presume therefore of somewhat less antiquity, are the two closely allied genera of Raillardia and Dubautia, which have a close relative in Raillardella of the Sierra Nevada in California. Then we come to the three genera, Tetramolopium, Lipochæta, and Campylotheca, that, being still in touch with the world outside, may be regarded as the latest arrivals of the early genera of the Compositæ. Tetramolopium, concerning which botanists were unable to agree, would seem, according to the Index Kewensis, to possess Mexican and Ecuadorian as well as Hawaiian species. Lipochæta, nearly related to other American genera, contains a dozen species, of which eleven are found only in Hawaii, whilst the twelfth occurs, according to the Index Kewensis, in California, and, according to Dr. Hillebrand, in the Galapagos group. Of the generic value of Campylotheca there seems a doubt, and its distinctness is scarcely recognised in the Index Kewensis. It is, however, closely allied to Coreopsis, an American genus represented, according to Drake del Castillo, in the Marquesas.

In the Tahitian region, that is to say in Eastern Polynesia, the genus Fitchia alone belongs to the early age of the Compositæ, so characteristic of Hawaii. Indications of the former widespread range of the genus over this region of the South Pacific are afforded by its being now represented by two species in Tahiti and by one species in Rarotonga, localities nearly 700 miles apart. It was thus regarded by Bentham, who saw in it a solitary remnant of the ancient South Pacific flora. Like the Hawaiian genera, as shown below, it is often restricted to the higher levels. Botanists differ about its affinities, and a discussion of the subject will be found on pages 20 and 66 of the Introduction to the Botany of the Challenger Expedition.

The restriction of these ancient genera of the Polynesian Compositæ to the upland regions is of some interest. “The preponderance of Compositæ among the high-level plants obtains almost throughout the world.” This observation was made by Mr. Hemsley in connection with the flora of the highlands of Tibet (Journ. Linn. Soc. Bot. vol. 35, 1902), where the Compositæ constitute about 19 per cent. of the flowering plants; and I may remark in passing that, according to Mr. Ball, one of the most conspicuous elements in point of frequency in the higher flora of the Great Atlas is presented by the Compositæ which make up between 12 and 13 per cent. of the whole flora (Hooker and Ball’s Marocco and the Great Atlas). This feature of alpine floras is brought into great prominence in Schimper’s recent book on Plant Geography.

Some of the most lasting reminiscences that the naturalist will bear away with him from the highlands of Hawaii are connected with the Compositæ. Those who have ascended the mountains of Mauna Kea and Mauna Loa, will remember that amongst the last plants occurring above the forest zone, and scattered about on the ancient lava fields at elevations exceeding 10,000 feet above the sea, are species of Raillardia and the beautiful “Ahinahina” (Argyroxiphium). It is, however, in the open, scantily wooded region, elevated 6,000 to 9,000 feet, and lying between the true forest zone below and the bare lava slopes above, that the shrubby and arborescent Compositæ of the large island of Hawaii are most at home. Such regions, as Hillebrand well describes (p. xxiv), are characterised by stunted trees, chiefly Sophora, Cyathodes, Myoporum, and others, associated with arborescent Raillardiæ of the order of Compositæ. Between them luxuriate other shrubby Compositæ of the genera Raillardia, Dubautia, Campylotheca, and Artemisia, together with Strawberries, Raspberries, and species of Vaccinium.

Botanists have not given us much account of the associates of the interesting genus Fitchia on the uplands of Tahiti. We learn, however, from Nadeaud that in his time these Composite trees and shrubs were spread over the higher region of the island of Tahiti above 800 and 1,000 metres. Cheeseman, to whom we are indebted for the discovery and the description of the Rarotongan species, tells us that this tree, which attains a height of 25 feet in the sheltered valleys, and is much dwarfed on the exposed ridges and hill-tops, often forms the greater part of the forest above 500 feet, and reaches the highest peaks of the island (2,250 feet).

In discussing the probable mode of dispersal of these early Composite plants of the Pacific we shall be treading on somewhat debatable ground. We will, however, point out that the mere possession of structures that could be utilised for dispersal of the seeds is not the only important question here involved. If we could demonstrate that all these genera possess exceptional capacities for distribution over the ocean, we should prove too much, since the process has been in the main suspended for ages. If, on the other side, it could be shown that their fruits are not at all suited for such dispersal, we should prove too little, since the ancestors of these genera must have been transported to these islands in some fashion or other. This clearly indicates that other important factors have also come into play in determining the distribution of the early Compositæ of the Pacific islands.

It was long ago pointed out by De Candolle that the possession of a pappus does not, as a rule, increase the area of a Composite plant, although as regards hooks and barbed appendages, such as occur in Bidens, the greater areas of the plants thus provided may be, as he thought, in some measure explained. Even in respect to hooks and barbs it would be easy to point to cases where, as Bentham remarks, unusual powers of adherence are by no means indicative of wide dispersal in all cases. In any event it will be also incumbent on us to explain why these genera no longer possess facilities for distribution. This suspension of the means of dispersal is not, however, peculiar to the age of the endemic genera of the Pacific islands. It is a character but in a less degree of the succeeding age, the age of genera found outside the group, but represented within it by endemic species; and from this we may suspect that we have had in operation in the Pacific an influence, far-reaching both in time and space, to which the agencies of dispersal have been compelled to adapt themselves, an influence which has acted as a distributor of the distributing agencies.

Coming to the fitness for dispersal of the achenes of the early Composite genera of the Pacific islands, it will be assumed that they have been, as a general rule, transported in birds’ plumage. The fruits are usually 2·5 to 12 millimetres (1⁄16 to 1⁄2 inch) in length, and are provided either with a pappus of soft or stiff bristles, or with awns or teeth, but these appendages vary much in size in the different genera and in different species of the same genus. The instance of Lipochæta is especially significant as indicating the alterations which the appendages of the achene may have undergone in the cases of other genera. With most species there are usually two or three teeth or short awns, but in some species these are obsolete, and in others they are long and stout.

Bearing these facts in mind we should hesitate to rely too much on the present condition of the achenes in the other genera as an indication of the fitness for dispersal of the fruits of their ancestors. In one genus, Campylotheca, which may be regarded as among the youngest of the genera, the achenes are provided with barbed or hooked awns which cause them to adhere as tenaciously to one’s clothes as in the case of those of Bidens, an allied genus. In Fitchia, the Tahitian genus, which may be looked upon as one of the oldest of the Pacific genera of Compositæ, the achene is furnished with two long awns or setæ, which, as Drake del Castillo observes, recall those of Bidens. The achenes of the other Hawaiian genera, as regards their fitness for dispersal in plumage, may be said to give less definite indications. In some, as in Dubautia and Raillardia, there is a typical pappus of ten to twenty long hair-like bristles. In others again, as in Wilkesia and Argyroxiphium, the pappus is much reduced, and in some species of Lipochæta it is, as above remarked, quite obsolete.

The chances of the achenes of the parent plants having in some cases been originally transported to the islands in the plumage of birds would be increased by a bird making its nest of the plant-materials or amongst the plants themselves, or by its pecking at the fruit-heads. In our own time different species of the grouse family on the slopes of the Californian and Columbian mountains make their nests on the ground under the shade of Artemisia bushes and find a portion of their sustenance in their fruits. Artemisias also form one of the features of the vegetation of the Hawaiian uplands; but since they present only specific differentiation they are referred to a later era. Yet it will be on the slopes of the Rocky Mountains and of the Californian Sierra Nevada, amongst the “sage-brush” and the grouse, that we may have to stand when we look in thought across the Pacific towards far distant Hawaii and ask ourselves whence came its tree-like Raillardias, its shrubby Dubautias, its tall Wilkesias, and the silvery Ahinahinas (Argyroxiphium).

It is possible that in some genera the achenes have, or had, a means of adhering to plumage through a “sticky” secretion, such as is sometimes found with Lagenophora, an Hawaiian genus of the next era, and also with the weed-plant Adenostemma viscosum; but this is a point that has not yet been investigated. Nor can we altogether exclude the chance of the achenes having in some cases been transported unharmed to Hawaii in a bird’s stomach. The possibility of this has been above implied in the case of Artemisia; and it is pointed out in [Chapter XXXIII]. that pigeons in Hawaii feed sometimes on the achenes of Compositæ. The Hawaiian goose (Bernicla sandwicensis) lives, according to Mr. Dole, on Sonchus asper, an introduced plant, as well as on berries (Wilson’s Aves Hawaiiensis). There are numerous references of this nature in books about birds, and it should always be remembered that birds in pecking at the fruit-heads scatter the seeds on their feathers. (See [Note 67].)

From the foregoing remarks it may, I think, be inferred that the achenes of the ancestors of the original Composite genera of the Pacific islands were in all probability not unfitted for transport by birds, more especially in their plumage. Some of my readers, however, may express a doubt as to whether birds likely to disperse seeds would be found in any numbers at the great heights where some of the continental Compositæ occur. But it is well known that birds of the grouse and partridge family frequent high levels in continental regions over much of the globe. Arborescent Compositæ are found at heights of 10,000 to 14,000 feet on the mountains of Central Africa; and it should be noticed that Sir Harry Johnston observed “francolins” on the slopes of Ruwenzori up to 13,000 feet (Uganda Protectorate, vol. 1; Trans. Linn. Soc. Bot., Ser. II. vol. 2). Sir Martin Conway in the Bolivian Andes found geese, ducks, gulls, snipe, &c., numerous in suitable places up to 17,000 feet (Journ. Roy. Geogr. Soc., 1899); whilst geese and teal were noticed by Sir Joseph Hooker and others at elevations of 17,000 feet in the mountains of Tibet (Hooker’s Himalayan Journals; Journ. Linn. Soc. Bot., vol. 35, p. 147). These are all birds, as shown in [Chapter XXXIII.], that are likely to disperse plants, and probably none more effectually than the goose, of which Hawaii possesses a particular variety or species. It may be remarked that geese, ducks, gulls, and other birds use Cotula plumosa in Kerguelen for making their nests (Dr. Kidder quoted by Mr. Dixon in his book on Birds’ Nests).

Sea-birds were probably the principal agents in carrying the achenes of the early genera of the Compositæ to Hawaii. Dr. Hillebrand attached importance to the tropic-bird (Phaethon) in the distribution of species (Introd., p. 30); and since these birds breed at the crater of Kilauea in Hawaii, 4,000 feet above the sea, and also high up in Tahiti (Moseley), its agency is not unlikely, I am inclined to think, however, that birds like the petrels and puffins, that in nesting burrow in the ground, choosing places where the vegetation is thickest, and where they would be likely to get seeds on their feathers, would be more efficient agents. This is the view expressed by Prof. Moseley in Wallace’s Island Life, p. 250. He considered that albatrosses, petrels, and puffins have played a great part in the distribution of plants, and to some degree especially account for the otherwise difficult fact that widely distant islands in tropical seas have similar mountain plants. Birds, he says, that in high latitudes, as at Tristan da Cunha and Kerguelen, often burrow near the sea-level, in the tropics choose the mountains for their nesting-place; and he refers to a puffin that nests on the top of one of the high mountains of Viti Levu at an altitude of 4,000 feet, to a petrel nesting among ferns at Tahiti at an elevation of 4,400 feet, and to another petrel breeding in like manner in the high mountains of Jamaica at a height of several thousand feet above the sea. He gives point to these interesting remarks, which might be supplemented by data from other parts of the world, by observing that it is not necessary that the same species should now cover the range of the plants concerned. The ancestor of the species might have carried the seeds, and the range of the genus is alone sufficient. It may be added that, as I have shown in [Chapter XXXIII.], sea-birds have been far more active agents in the distribution of plants than many people might imagine. The more recent observations of Ekstam in Spitzbergen have thrown considerable light on this subject.

Having in the first place formed the opinion that the achenes of the early Hawaiian Compositæ are suited for dispersal by birds, and then shown that sea-birds were probably the principal agents, we are met with the curious difficulty that in the case of the early Hawaiian genera of Compositæ the complete suspension for ages of the means of dispersal is involved in the circumstances that these genera are confined to the Hawaiian group. We can attribute to the agency of existing sea-birds the occurrence of the genus Lagenophora in the uplands of Hawaii, on the mountain-tops of Fiji, and in Australia and New Zealand; but the agency of birds as at present in operation does not assist us except indirectly in the case of the genera restricted to Hawaii or to Tahiti. Is it possible, we may inquire, to penetrate this mystery? Why, we may ask with Mr. Hemsley, has the agency ceased acting, and why have its operations been confined to the conveyance of seeds to the islands and not from the islands as well (Intr. Bot. Chall. Exped., p. 66)? I need scarcely add that the same question presents itself with all the other peculiar genera of these islands, and in fact with endemic genera all over the world. What can be stranger, it may be remarked, than the limited distribution of the Pandanaceous genus Sararanga in the Western Pacific, although suited for dispersal by frugivorous birds. This is not, indeed, a special difficulty connected with oceanic islands; it applies to the whole plant-world; yet it is possible that, as it is exhibited by the Compositæ in these islands, we may be in a better position to grapple with the problem. But before doing so it will be requisite to look a little closer at these early Hawaiian genera of the Compositæ.

The distribution within the archipelago of the genera and species of the early Compositæ of Hawaii is worthy of notice from the light it throws, not only on the relative antiquity of the genera, but also on the subsequent conditions of isolation. Of the nine genera here referred to five are distributed over most of the islands of the group. These include all the genera possessing a number of species, namely, Tetramolopium with seven species, Lipochæta with eleven, Campylotheca with twelve, Dubautia with six, and Raillardia with twelve species. Of the four genera remaining all have only two species, and are restricted to two or three islands, Remya and Wilkesia being in both cases found in Kauai and Maui, whilst Argyroxiphium is confined to the adjacent islands of Maui and Hawaii, and Hesperomannia to those of Oahu, Lanai, and Maui. These four genera that are restricted to only two or three islands are the same before referred to as regarded by Hillebrand as the oldest, partly on account of their isolated generic position, and partly because in each case they only possess two species.

Although the early Hawaiian Compositæ were evidently originally transported to most of the islands of the group, it is noteworthy that their subsequent isolation from the rest of the world has in the later ages been repeated within the limits of the archipelago. Of the 56 species, all of which are now endemic, 28, or just half, as shown in the table on the following page, are confined to a single island. Of the remainder, almost all are restricted to two or three adjacent islands. Hillebrand gives only a solitary species, Lipochæta connata, as occurring in all the islands. This suspension, to a great extent, of the means of dispersal between the islands is also strikingly illustrated by the Lobeliaceæ.

We have only to mention the flora of Fiji and those of the adjacent groups of Samoa and Tonga to exclude them from any share in the early era of the Compositæ in the Pacific. The prevailing adventitious character of the Fijian Compositæ is indicated in the fact that the species of the majority of the genera are included by Seemann in his list of Fijian weeds. There are only one or two Fijian Compositæ, such as the mountain species of Lagenophora and the littoral species of Wedelia, that merit the special attention of the student of dispersal. So also with Samoa, Reinecke enumerates eight species, of which six are weeds either of aboriginal or of European introduction, the others being the littoral Wedelia above alluded to, and a species of Blumea found also in Fiji.

Distribution of the Endemic Genera of Compositæ in the Hawaiian Islands.

Genus.Distribution of the Species.Total.
One island.Two islands.Three islands.Four islands.General.
Remya2————2
Tetramolopium142——7
Lipochæta343—111
Campylotheca543——12
Argyroxiphium11———2
Wilkesia2————2
Dubautia4—2——6
Raillardia91—2—12
Hesperomannia11———2
2815102156

We have now, I venture to think, gone far to establish the existence of an early “Composite” flora with mainly American affinities in the Pacific islands, an ancient flora of which only the remnants now occur in the uplands of Hawaii, Tahiti, and Rarotonga. That the achenes were originally transported in birds’ plumage is, as we have seen, probable; but we are still quite in the dark as to the causes of the subsequent suspension of the means of dispersal and of the resulting period of isolation, during which the original immigrant plants acquired their endemic characters. In our uncertainty, therefore, we will look to Fiji in the hope that in the absence of the early Compositæ from that group we may find a clue that will enable us to divest this problem of some of its difficulties.

It might be at first considered that since these peculiar genera of Compositæ occur in the higher levels of Hawaii and Tahiti their absence from Fiji might be connected with the relatively low altitude of those islands, a character that is concerned with the exclusion from the Fijian flora of many Hawaiian and Tahitian mountain plants (see Chapters [XXIII.] and [XXIV.]). But this view is at once negatived by the fact that Fitchia thrives in Rarotonga, an island which does not far exceed 2,000 feet in elevation. It is negatived also by the extensive development of shrubby and arborescent Compositæ in the Galapagos Islands, on the equator, in St. Helena in 16° South latitude, and in other tropical islands, which are less than, or do not exceed, the Fijian Islands in their altitude.

During the age of the Compositæ it is reasonable to suppose that the dispersal was general over the Pacific. The absence of genera indicating this era from the islands of the Fijian region, that is, from Fiji, Tonga, and Samoa, would become intelligible if these groups were submerged during this age of the general dispersal of the order over this ocean. In my volume on the geology of Vanua Levu in Fiji, I have shown that these island-groups of the Western Pacific emerged from the sea towards the close of the Tertiary period, a conclusion that would enable us to assign the age of the general dispersal of the Compositæ over the tropical Pacific to an earlier portion of the same period.

In order, however, to make further progress in the discussion of this difficult problem we are obliged to approach it from the outside. We must in fact regard these genera from the standpoint of their position as members of the vast and ancient order of the Compositæ. It is now more than thirty years since Mr. Bentham completed his remarkable memoir on the classification, history, and geographical distribution of the Compositæ (Journal Linnean Society, Botany, London, Vol. 13, 1873). Like De Candolle, when dealing with the facts of distribution, he handled thousands of species, and as a result he drew certain inferences which are of prime importance to students of plant-dispersal. In his time the order included nearly 10,000 known species, and although this number has since no doubt been considerably increased, it is not likely that his main conclusions, in so far as they are free from purely hypothetical considerations, will be materially affected by the later discoveries.

Accepting the antiquity of the order, and regarding it as probably dating far back in geological time, he observes that the evidence points to a very wide dispersion of its original stock at an early period. Africa, West America, and possibly Australia, possessed the order at the earliest recognisable stage. There must have existed, he contends, at this early period some means of reciprocal interchange of races between these regions. Then followed a stoppage of communication, or a suspension of the means of dispersal, between the tropical regions of the Old and New Worlds; but long after communication was broken off in the warmer regions, it still existed, as he holds, between the alpine heights in those regions and also between the high northern latitudes of both hemispheres. Referring particularly to the Hawaiian Group, he considers that the large endemic element among the Compositæ indicates that the ancient connection, whether with America or with Australasia, has been so long severed as not to have left a single unmodified common form. Fitchia, the Tahitian genus, as we have already remarked, is regarded as the only remnant of an ancient Composite flora in the tropical islands of the South Pacific.

In the light of these reflections it will be interesting to glance at the general distribution of the shrubby and arborescent or woody Compositæ. Mr. Hemsley, having generally discussed the subject, arrived at the conclusion that, “although they form so large a proportion of the floras of St. Helena, Juan Fernandez, the Sandwich Islands, and some other islands, they are not specially insular.” There are scores of them, he goes on to say, in South America, Africa, Madagascar, India, Australia, and New Zealand from twenty to forty feet high, and more truly arboreous than the insular ones; whilst nearly every sub-order has its arboreous representatives. He was, however, unable to form any definite opinion of the method of distribution of the woody Compositæ. Taking those of St. Helena and Juan Fernandez, he observes that they are not more closely allied to the Compositæ of the nearest continents than they are to those of more distant regions. The occurrence of arboreous Compositæ, belonging in each case to different tribes, in so many remote oceanic islands, coupled with the distribution of the genera to which they bear the greatest affinity, seems, he observes, to indicate that they are the remains of very ancient types (Introd. Bot. Chall. Exped., pp. 19-24, 66, 68; also Parts ii. p. 61, and iii. p. 23).

The further discussion of this subject would lead us into a wide field of inquiry, quite beyond the scope of this work. There is, however, an inference that I think we may legitimately draw from geological evidence in this region. With respect to the antiquity of the woody Compositæ of the Pacific as illustrated by the endemic genera, both Mr. Bentham and Mr. Hemsley view them as belonging to ancient types. Mr. Wallace, in his Island Life, a book that becomes more and more indispensable for the student of dispersal as years progress, dwells on the importance of these ancient Compositæ in the floral history of the Pacific islands. We may look upon the Hawaiian Compositæ, he remarks, as representing the most ancient portion of the existing flora, carrying us back to a very remote period when the facilities for communication with America were greater than they are now. The date of this period of oceanic dispersal of the Compositæ we can now approximately determine, since these plants are absent from the Fijian region, an area of submergence during the Tertiary era. Before the island-groups of the Fijian region had emerged towards the close of the Tertiary period the achenes of the early Compositæ had been dispersed far and wide over the tropical Pacific.

But this is not all that we can infer from the convergence of these independent lines of botanical and geological investigation. Mr. Bentham observes that the tribes of the Compositæ had acquired the essential characters now employed in classification before the dispersion of the order over the Pacific. Since this general dispersion took place, as we hold, during the Tertiary submergence of the island-groups of West Polynesia (Fiji, Tonga, Samoa), it follows that the birth of the tribes of the Compositæ antedates that period. If this interesting order could supply us with a “datum-mark” in the history of the Pacific floras, it would be stated in terms of the development of specific and generic characters, but not of those of a tribe.

Summary of Chapter.

(1) The Hawaiian Islands present the same contrast with the Fijian and Tahitian groups as regards the development of new species in the case of the flowering plants that they offer in the case of the vascular cryptogams (ferns and lycopods). But the contrast is intensified, and it is further emphasised as respecting the flowering plants by the evolution of a large number of endemic genera.

(2) This great preponderance of peculiar species and genera in Hawaii is not to be connected with the relative antiquity of the group but with its degree of isolation.

(3) The earliest stage of the flowering plants of the islands of Hawaii and of Eastern Polynesia (the Tahitian region) is indicated by the endemic genera, particularly those of the Compositæ and Lobeliaceæ. Such genera are numerous in Hawaii, and occur also in the Tahitian region, as in Tahiti and Rarotonga; but do not exist in the groups of the Fijian region (Fiji, Tonga, and Samoa).

(4) The endemic genera of the Hawaiian Compositæ are mainly American in their affinities. The relationship of the solitary Tahitian genus (Fitchia) is still a subject of discussion.

(5) In the Hawaiian Islands, as well as in Tahiti and Rarotonga, the plants of the endemic genera of Compositæ are, as a rule, arborescent or shrubby; and in the first two localities they are mainly restricted to the higher levels.

(6) In discussing the mode of dispersal of the achenes of the original genera we have also to explain why the process of dispersal has been in the main suspended.

(7) It is shown that the achenes of these early Compositæ were in all probability suited for dispersal in birds’ plumage.

(8) Yet the isolating influence that cut off these genera from the outside world has, in later ages, been active within the limits of the Hawaiian archipelago, with the result that half the species are not found in more than a single island. Inter-island dispersal has, therefore, been also largely suspended.

(9) The absence of endemic genera of Compositæ from Fiji, Tonga, and Samoa cannot be attributed to unsuitable climatic conditions connected with the relatively low elevation of those islands as contrasted with those of Hawaii, since a species of Fitchia abounds in Rarotonga, which is not far over 2,000 feet in elevation. Shrubby and arborescent Compositæ of peculiar types also occur in the Galapagos and other tropical islands not more elevated than the Fijis.

(10) These endemic genera are the remains of an ancient Composite flora in the islands of the tropical Pacific, and ages have elapsed since the severance of their connections with regions outside.

(11) According to Mr. Bentham the Compositæ were distributed over Africa, West America, and possibly Australia, at an early period, but subsequent to the differentiation of the tribes of the order. Some means of reciprocal interchange of races between these regions then existed. Then followed a suspension of the means of dispersal between the tropical regions of the Old and New Worlds except between the alpine heights of those latitudes.

(12) It is inferred by the author of this volume that the general dispersion of the early Compositæ over the Pacific took place during the Tertiary submergence of the island-groups of the Fijian region (Fiji, Tonga, and Samoa), and that their absence from that region may be thus explained. At the time of this general dispersion, as above pointed out, the tribes of the Compositæ had been already differentiated.

CHAPTER XXII
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.

Genus.No. of species.Distribution of genus.Distribution in the group.Height of plant.Nature of Station.
Elevation. Station.
Brighamia1Endemic.Molokai, Niihau.5 to 12 feet.Islands not exceeding 3,500 feet.Steep palis or mountain gaps.
Lobelia5Non-endemic.General.4 to 6 feet.2,000 to 6,000 feet.Bridges, gulches and woods.
Clermontia11Endemic.General.Usually 10 to 20 feet.[[2]]2,000 to 6,000 feet.Open woods.
Rollandia6Endemic.Oahu.Usually 4 to 6 feet, one species 10 to 15 feet.Higher parts of Oahu, which is 4,000 feet high.Woods.
Delissea7Endemic.General.5 to 10 feet.1,000 to 5,000 feet.Woods and gulches.
Cyanea28Endemic.General.Usually 6 to 15 feet.[[3]]1,000 to 5,000 feet.Woods, ravines, gulches.
East Polynesian or Tahitian Islands.
Sclerotheca4Endemic in E. Polynesia.Tahiti, Rarotonga.6 to 25 feet.1,500 to 3,000 feet.Humid wooded slopes.
Apetahia.1Endemic.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:—