CHAPTER XXVI

THE MALAYAN ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS (_continued_)

THE AGE OF WIDE DISPERSAL OVER THE TROPICAL PACIFIC (_continued_)

The widely dispersed genera that are as a rule not entirely represented by endemic species in any archipelago.—Elæocarpus.—Dodonæa.—Metrosideros.—Alyxia.—Alphitonia.—Pisonia.—Wikstrœmia.—Peperomia.—Eugenia.—Gossypium.—The last stage in the general dispersal of plants of the Malayan era as illustrated by the widely-dispersed genera having as a rule no peculiar species.—Rhus.—Osteomeles.—Plectronia.—Boerhaavia.—Polygonum.—Pipturus.—Dianella.—Summary.

A LATER period in the era of the general dispersal of Malayan plants over the Pacific is indicated by those genera that as a rule are never entirely represented by endemic species in any archipelago. Hawaii now comes into touch with the world outside, and all the groups possess some connecting link. But the beginning of the effect of the isolating influence is shown in the association in each principal archipelago of peculiar species with those that occur in other groups.

We see here illustrated in all but the final stage that process by which a solitary widely-ranging species, alone representing its genus, becomes ultimately in each group the parent of a number of peculiar species. The polymorphous, or extremely variable, species plays in this period the all-important part. The earliest stage is exhibited by such genera as Alphitonia, Dodonæa, Metrosideros, Pisonia, and Wikstrœmia, that possess in the tropical Pacific a solitary widely-ranging species, varying independently in every group and giving rise to forms that, in their degree of differentiation, sometimes approach a specific value. Later stages are shown when the polymorphous species, having done its work of distributing the genus, settles down and “differentiates” in every group; and this we see now illustrated in the genera Elæocarpus, Alyxia, Peperomia, and others.

The bulk of the genera of this period, of which only a few can be mentioned here, hail from the tropics of the Old World through Malaya. Thus Alyxia, Elæocarpus, Morinda, and Wikstrœmia are Malayan; whilst genera like Eugenia, Peperomia, and Pisonia, that occur in the Old and New Worlds, can similarly be traced to the Asiatic side of the ocean by the distribution of their species. Others again have their home in New Zealand like Metrosideros, or in Australia, as with Dodonæa and Scævola. None are exclusively American. Some of the genera, as Morinda and Scævola, have littoral as well as inland species; but, as shown in