Species richness and endemism in the Western Australian flora

Aim Estimates of endemic and non-endemic native vascular plant species in e ach of the three Western Australian Botanical Provinces were made by East i n 1912 and Beard in 1969. The present paper contains an updated assessment of species endemism in the State. Location Western Australia comprises one third of the continental Australia n land mass. It extends from 13 degrees to 35 degrees S and 113 degrees to 129 degrees W. Methods Western Australia is recognized as having three Botanical Provinces (Northern, Eremaean and South-West) each divided into a number of Botanica l Districts. Updated statistics for number of species and species endemism in each Province are based on the Census of Western Australian Plants data base at the Western Australian Herbarium (Western Australian Herbarium, 199 8 onwards). Results The number of known species in Western Australia has risen steadily over the years but reputed endemism has declined in the Northern and Erema ean Provinces where cross-continental floras are common. Only the isolated South-West Province retains high rates of endemism (79%). Main conclusions With 5710 native species, the South-West Province contains about the same number as the California Floristic Province which has a sim ilar area. The Italian mediterranean zone also contains about this number b ut in a smaller area, while the much smaller Cape Floristic Region has almo st twice as many native species. The percentage of endemic species is highe st at the Cape, somewhat less in south-western Australia and less again in California. Italy at 12.5%, has the lowest value. Apart from Italy, it is u sual for endemism to reach high values in the largest plant families. In We stern Australia, these mainly include woody sclerophyll shrubs and herbaceo us perennials with special adaptations to environmental conditions. While t hose life forms are prominent in the Cape, that region differs in the great importance of herbaceous families and succulents, both of which are virtua lly absent from Western Australia. In California and Italy, most endemics a re in families of annual, herbaceous perennial and soft shrub plants. It is suggested that the dominant factor shaping the South-West Province flora i s the extreme poverty of the area's soils, a feature that emphasizes sclero phylly, favours habitat specialization and ensures relatively many local en demic species.