Observations of a Naturalist in the Pacific Between 1896 and 1899, Volume 2 / Plant-Dispersal

by H. B. Guppy

Grouping of the Plant-Genera of the Islands of the Tropical Pacific that possess both Littoral and Inland Species.

Section I. Where the littoral and inland species are most probably of independent origin, both possessing their own means of dispersal; Calophyllum, Hibiscus, Colubrina, Morinda, Scævola, Cordia, Ipomœa, Vitex, Tacca, Casuarina.

Section II. Where the littoral species have probably given rise to inland species, and both still exist in the group of islands: Vigna, Premna.

Section III. Where inland species have been probably developed from littoral species no longer existing in the group: Canavalia, Erythrina, Sophora, Ochrosia.

Section IV. Where the littoral and inland species are evidently of independent origin, and there is no means of accounting for the existence of the inland species by agencies of dispersal at present in operation: Barringtonia, Pandanus.

Section V. Where in the same genus some inland species are derivatives of the coast species and others are of independent origin: Guettarda.

Section VI. Where the coast species, having little or no capacity for dispersal by currents, are regarded as derived from the inland species in one group of islands and as afterwards distributed to those in the vicinity: Eugenia, Drymispermum, Acacia.

Section I

This group, which includes those genera where the coast and inland species are regarded as of independent origin, both possessing their own means of dispersal, contains about half of the total number of genera here concerned. We will first deal with the genera Calophyllum, Morinda, and Scævola, where the littoral species have buoyant fruits or seeds that are dispersed by currents, whilst the inland species have more or less non-buoyant fleshy fruits that could only be dispersed by frugivorous birds. Here the inland and coast species could have arrived independently at the island, and we are not called upon either on this ground or by reason of affinity of characters to connect the one with the other.

The genus Scævola is very typical of its kind and has been already in part discussed in [Chapter II.] The wide-ranging shore-species, S. Kœnigii, that is distributed over the Pacific may sometimes, as in Hawaii, be accompanied by numerous inland species, all endemic, seven of them being enumerated by Hillebrand; or, as in Fiji and Tonga, there may be associated with it a solitary inland species, S. floribunda (see [Note 51]); or, as in Tahiti, it may exist by itself. On the other hand, as in the Kermadec Islands, a single inland peculiar species may alone represent the genus. The inland species have fleshy drupes which, as far as examined, have no floating power and possess no buoyant tissues in their coverings; and their independent dispersal by birds cannot be doubted. The endemic character of most of the inland species of the Pacific islands is most probably due to the suspension of the transporting agency of frugivorous birds, just as the wide range of the solitary littoral species may be attributed to the uninterrupted agency of the currents. There is nothing in the description of the endemic species given in Hillebrand’s Hawaiian Flora to indicate any especial genetic connection between the inland species and the beach plant, S. Kœnigii; and the occurrence of a solitary inland peculiar species in the Kermadec Islands clearly proves an origin independent of any littoral plant.