Transoceanic Dispersal in Sophora and other Genera

Abstract

THE existence of the same species in countries widely separated by oceans, an apparent exception to the hypothesis of single centres of creation, was explained by nineteenth century naturalists in two ways: by transoceanic dispersal or by continental extension. Darwin supported the first explanation, and argued against major continental extensions so recent as to be “within the period of existing species”1. Explanations by continental drift can be criticized on the same grounds2. But in most widely dispersed species we still lack detailed knowledge of the seed and its means of dispersal. Thus the possibility of long-distance dispersal by ocean currents of seed of certain species of Sophora (Papilionaceae) has long been discussed. Studies of S. tomentosa, a pan-tropic littoral species with buoyant seeds, show that this species must certainly be distributed in this way3–5; and since Darwin's time there has been speculation as to whether the close relation between the sophoras of New Zealand, southern Chile and Gough Island can be explained in the same way. We made the following observations on the problem on the Kermadec Islands (W. R. S.) and in New Zealand and southern Chile (E. J. G.).