Spatial distribution of species richness and endemism of the genus Acacia in Australia

The aim of this study is to identify and map the spatial distribution of species richness and endemism of the genus Acacia in Australia. A database of 171 758 geo-referenced herbarium records representing 1020 Acacia species was assembled and aggregated to a 0.25 degrees grid cell resolution. A neighbourhood analysis of one-cell radius was applied to each of the grid cells to map the spatial patterns of species richness and endemism. The primary centres of species richness are in accordance with previous results, occurring in the South-West Botanical Province in Western Australia, the MacPherson-Macleay overlap and the Central Coast of the Sydney Sandstone region. We identify 21 centres of endemism, of which six were previously unrecognised. The primary centres of endemism are located in South-West Western Australia, the Kimberley District and the Wet Tropics in Queensland. The South-West Botanical Province in Western Australia contained the greatest number of regions with the highest number of endemic species of Acacia. A randomisation test showed that our 21 centres of endemism were significantly different from random. The majority of centres of Acacia endemism were incongruent with the centres of species richness, with only three grid cells in the top 1% for both measures. We also confirm that South-West Western Australia is a region of very high species richness and endemism, in accordance with its status as a global hotspot of biodiversity.