Phytogeography of Acacia in Western Australia

Abstract

Distributions of the 373 described and c. 113 undescribed species of Acacia occurring in Western Australia were plotted on state maps divided into 1° latitude by 1.5° longitude grids. The number of species per grid was determined, and species richness was shown to be highest along the inland eastern margin of the South-West Botanical Province. Minor centres of richness were found associated with mountainous areas of the Pilbara Region, Desert Region and Northern Botanical Province. It is proposed that the centres of species richness have been foci of recent evolutionary divergence and also refugia favouring the persistence of some relict forms. It is suggested that recent speciation has been promoted by recurrent migration, extinction and isolation of populations as a result of Pleistocene climatic fluctuations and their erosional consequences in climatically transitional areas.

An analysis of the distribution of selected closely related species groups occurring in a range of habitats throughout Western Australia indicates that geographical isolation has played an important role in speciation in the genus.