Geography and dispersal of Galapagos Islands vascular plants

Abstract

NEARLY every naturalist who has dealt, with the Galapagos Islands since Darwin1 has pointed out the flora's obvious geographical affinities with tropical America, stressing relationships with South America, Mexico, Central America and the West Indies. But as the tropical American flora has become better known, most Galapagos species once thought to be only Mexican, Central American or West Indian in their extra-Galapagean distributions also have been found to occur in northern and western tropical South America (for example, the widespread Zanthoxylum fagara (L.) Sarg., Rutaceae) or to have been incorrectly identified (for example, the endemic Chamaesyce viminea (Hook, f.) Burch, Euphorbiaceae). Svenson2 first indicated the flora's lack of affinity with Mexico and Central America. The study reported here is the first to present evidence that West Indian relationships do not exist. After publication of the Flora of the Galapagos Islands3 and several subsequent papers4–12, it is now also possible to quantify the geographical relationships of the vascular flora and to study the plants' dispersal mechanisms. This study shows the flora's relationships to be with adjacent South America and and that birds have had the most important role in plant dispersal to the islands.