BRUNET, JOHANNE* AND AARON LISTON. Department of Botany and Plant Pathology, Oregon State University , Cordley Hall 2082, Corvallis, OR 97331- 2902. - Breeding system evolution in the genus Thalictrum (meadow rue) Ranunculaceae.
The phylogeny of 20 Thalictrum species and four outgroups was
reconstructed using two molecular loci, the nrDNA ITS region (internal
transcribed spacers of nuclear ribosomal DNA) and the chloroplast DNA
rpl16 intron, and 37 morphological characters. The 20 species
represent 10 of 14 sections in this genus of 190 species. The nuclear
data provided better-resolved trees than the morphological data. The
combined analysis consensus tree had bootstrap support above 70% for
the majority of clades. Thalictrum species vary in their
breeding system and pollination mechanisms within a breeding system.
Species can be hermaphroditic (all flowers have both male and female
organs), dioecious (male and female individuals), or andromonoecious
(male and hermaphroditic flowers on an individual) and are pollinated
by wind, insect, or both. While wind-pollination is common in
dioecious and andromonoecious species, and insect-pollination in
hermaphroditic species, both insect- and wind-pollination occur in
some dioecious and some hermaphroditic species. The evolution of the
breeding system and the pollination mechanism were examined using the
methods of character optimization. Two separate origins of dioecy were
detected in North America, and no reversal back to hermaphroditism was
observed. There was one origin of andromonoecy, and it was separated
from the origins of the dioecious clades. Of the known ecological
correlates of dioecy (woodiness, fleshy fruits, islands, tropical
habitats, and wind-pollination), only wind-pollination is correlated
with dioecy in this genus. Preliminary results suggest that
wind-pollination preceded the evolution of dioecy and andromonoecy in
this genus.
Key words: breeding system evolution, character optimization, phylogeny, pollination, Ranunculaceae, Thalictrum