MAST, AUSTIN R.* AND THOMAS J. GIVNISH. Department of Botany, University of Wisconsin, Madison, WI 53706. - Historical biogeography of Banksia and Dryandra (Proteaceae) in Australia’s Southwest Botanical Province.
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