SOLTIS, DOUGLAS E.*, LARRY HUFFORD, AND ROBERT K. KUZOFF. School of Biological Sciences, Washington State University, Pullman WA 99164. , Section of Molecular and Cellular Biology, University of California, Davis CA 95616. - Gynoecial diversification in Saxifragaceae: clarifying the evolution of epigyny.
Variation in the gynoecia of Saxifragaceae provides an excellent
system to explore the implications of developmental change in the
generation of floral diversity within a phylogenetic framework. The
traditional view has been that ovary position evolves from superior to
inferior. Saxifragaceae are of interest because the complete range of
ovary positions, from superior to inferior, has been reported not only
across the family, but within individual genera. Most angiosperms
with superior ovaries have an hypogynous floral ground plan and,
hence, have ovaries that are "truly superior." In contrast,
most inferior ovaries arise from an appendicular epigynous ground
plan. Using a phylogenetic hypothesis based on 6-genes, we found that
the evolution of ovary position in the family is complex, with
evolution to greater inferiority occurring in some taxa, whereas in
other instances there is evolution toward increasing superiority.
Significantly, we found that members of Saxifragaceae reported to have
superior ovaries actually possess an appendicular epigynous ground
plan. Hence, these taxa do not have truly superior ovaries; rather,
they represent "superior mimics." Furthermore, all gynoecia
in Saxifragaceae are technically inferior. Our data also indicate
that differences in ovary position at anthesis are a result of
allometric shifts in the growth proportions of the superior vs.
inferior regions of the ovary. These results have broad
implications, potentially providing insights into gynoecial
diversification throughout the angiosperms.
Key words: floral ontogeny, gynoecial diversification, Saxifragaceae