The largely Australian genus Hibbertia, containing ca. 150 species, has been characterized in the literature as containing a far greater amount of morphological variation with respect to floral bauplan, growth habit, and range of ecological adaptations than perhaps any other group of similar taxonomic rank. A familial-level phylogenetic analysis of Dilleniaceae utilizing sequences of the chloroplast gene rbcL strongly supports the monophyly of Hibbertia as currently conceptualized. Simultaneous maximum parsimony analysis of three data sets--cpDNA (rpl16 intron), nrDNA (ITS 1-2), and morphology--resolves two major clades within the genus that, with at least two notable exceptions, mirrors the morphological dichotomy of species with actinomorphic versus zygomorphic androecia and gynoecia. Hibbertia from the isolated, Mediterranean-climate region of southwestern Western Australia are largely clustered into a few large clades embedded within a grade of taxa indigenous to the eastern states of Australia. Western Australian species from these different clades frequently occur sympatrically, with different clusters of species found throughout the many vegetation types occurring in this part of the continent. In the extensive sclerophyllous shrublands (kwongan) occurring on nutrient-poor sands, sympatric Hibbertia species may show striking convergence on similar ericoid leaf forms, yet each co-occurring species will possess fundamentally different floral bauplans that are characteristic of its respective clade. This pattern of diversification is consistent with the concept of "leapfrogging" adaptive radiations put forth by Chase and Palmer (1997).

Key words: adaptive radiation, biogeography, Dilleniaceae, Hibbertia