The largest genus of the Leguminosae, widely distributed in tropical and subtropical regions of the world, most common in Africa and Australia with approximately 900 species. In Australia this genus is widespread and abundant throughout the continent and is dominant especially in the arid and semi-arid regions. Recent estimates put the number of species in Australia at about 660 (S. D. Hopper and B. R. Maslin 1978) with quite a significant number still remaining undescribed.<P><b>Species distribution</b><P>The phytogeography (distribution) of <I>Acacia</I> species in Western Australia was presented by Hopper & Maslin (1978). The paper should be referred to for full details which are only partly relevant to South Australia. They demonstrate extreme species richness on the inland eastern margin of the South-West Botanical Province. Minor centres were found in the Pilbara, Desert and Northern Botanical Provinces. Approximately 80% of the 500 species occurring in Western Australia are confined to that area.