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. Contrary to 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 their 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 geographical distribution suggest rapid speciation of
dioecious populations with changes in ecological conditions.
Key words: dioecy, mating system, monoecy, phylogeny, Siparunaceae