WON, HYOSIG* AND SUSANNE S. RENNER. Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121. - Why so many dioecious species in Siparunaceae (Laurales)?
Siparunaceae are tropical evergreen shrubs or trees, composed of 2
genera and ~70 species. Different from other families in Laurales, which show
diverse mating systems, flowers of Siparunaceae are strictly unisexual,
with plants monoecious or dioecious. More than 60 species are dioecious,
while 12 species are monoecious. A few morphological characters covary
with mating system. To trace the evolution of dioecy in Siparunaceae, we
reconstructed a phylogeny using cpDNA trnL-trnF IGS and nrDNA ITS
sequences, and diverse outgroups. The phylogeny strongly supports
monophyly of Siparunaceae and evolution of dioecy from monoecy within Siparuna.
Dioecious Glossocalyx is placed as sister to all other Siparunaceae,
while the dioecious Siparuna species form a clade nested higher up in the
tree. This phylogeny is congruent with the geographical distribution of
Siparunaceae; monoecious species are distributed in the Amazonian
lowland, while most dioecious species are found at higher altitudes in the Andes.
Relatively small sequence divergences among the dioecious species and
their geographical distribution suggest rapid speciation of dioecious
populations with changes in ecological conditions.
Key words: dioecy, mating system, monoecy, phylogeny, Siparunaceae