HORN, JAMES W. Department of Botany, Box 90338, Duke University, Durham, NC 27708. - Phylogeny, biogeography, and patterns of morphological evolution in Hibbertia (Dilleniaceae).
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