SWENSEN, SUSAN M.1*, WENDY L. CLEMENT1, LAURA L. FORREST2, and MARK C. TEBBITT3. 1Ithaca College, Ithaca, NY; 2Royal Botanic Garden Edinburgh, Scotland; 3Brooklyn Botanic Garden, Brooklyn, NY. - Hillebrandia sandwichensis: Evolutionary relationships and biogeography.
Hillebrandia is a monotypic genus of the Begoniaceae, a family
that currently includes two other genera, Begonia (1400
species) and Symbegonia (12 species). Hillebrandia is
distinguished by its semi-inferior ovary, which is fully inferior in
other Begoniaceae, and by the presence of 8-10 perianth segments
compared to 2-5(8) perianth segments in other members of the family.
In addition, Hillebrandia is the only begonia that is endemic
to the Hawaiian Islands. Parsimony-based phylogenetic analyses of
nuclear-encoded genes (ribosomal 18S and ITS, the internal transcribed
spacer region) and chloroplast-encoded genes (rbcL and the atpB-rbcL
spacer region) place Hillebrandia at the base of a clade that
includes the remainder of family Begoniaceae. Begoniaceae are globally
distributed in the tropics, but lack a fossil record to indicate its
age or geographic origin. Molecular studies have indicated that
Begonia had its origins in Africa and the African begonias are
the closest species to Hillebrandia. By comparing rbcL
sequences from Hillebrandia and two African begonias, and by
using fossil information from close outgroup species, we have
estimated the divergence time of Hillebrandia and
Begonia to be approximately 40 million years ago, an age that
predates the oldest of the current Hawaiian Islands. Our data suggest
that Hillebrandia is an island relict on a relatively young
archipelago. Various hypotheses as to Hillebrandia’s origin are
considered.
Key words: Begoniaceae, biogeography, Hillebrandia sandwichensis, phylogeny