Sixty-three of the seventy-nine species of Banksia and all ninety-three species of Dryandra are restricted to Australia’s Southwest Botanical Province. The Province – isolated from the rest of the continent by Australia’s arid middle – is one of the world’s great centers of floristic endemism (80% of the 4000 native species are endemic). Our cpDNA and nrDNA sequence data strongly support the paraphyly of Banksia with respect to a monophyletic Dryandra. Dryandra and the lineage of southwestern banksias from which it arose appear to form the largest documented radiation of plants wholly restricted to the region. We examined the historical processes generating this diversity by (1) defining areas of endemism and then (2) using cladistic biogeography to identify relationships among these areas. We analyzed presence/absence data for >130 taxa of Banksia and Dryandra in 170 50 km x 50 km cells using clustering and ordination techniques, as well as parsimony analysis of endemism. Cells with the greatest diversity of Banksia and Dryandra center around the northern and southern sandplains (as has been shown for Banksia alone by Byron Lamont). When areas of endemism are plotted onto the cladograms, we see at the broad scale several migrations (dispersal and/or vicariance with subsequent extinction) of ancestral taxa from the southern to the northern sandplains. Within Banksia, migrations in the reverse direction appear largely limited to range expansions of widespread species. At a finer scale, we are examining the importance of the Stirling and Barren Ranges (southern sandplains) and the Mt. Lesueur region (northern sandplains) as local refugia during climatic fluctuations.

Key words: areas of endemism, Australia, Banksia, cladistic biogeography, Dryandra, molecular systematics