WHITLOCK, BARBARA A. Harvard University Herbaria, Cambridge, MA 02138. - Phylogenetics of Byttneria and Ayenia (Sterculiaceae or Malvaceae s.l.): Biogeography and evolution of growth form in a large group of tropical woody plants.
The genera Byttneria and Ayenia (Sterculiaceae or
Malvaceae s.l.) are characterized by their unusual fly-pollinated
flowers, with five petals that are clawed at the base and apically
adnate to the top of the staminal column. The only character that
consistently can be used to distinguish these two genera from each
other is the number of anther thecae (two in the pantropical
Byttneria and three in the exclusively neotropical
Ayenia). Although basic construction of the flowers remains
remarkably constant, habit and leaf morphology show extraordinary
variation. Phylogenetic analyses of chloroplast DNA sequences
indicate that Ayenia is monophyletic and nested within
paraphyletic Byttneria. These results have important
implications for the evolution of stamen number and further
demonstrate the plasticity of this character within Byttnerioideae.
This study contributes to a growing body of empirical work that
examines the biogeography of tropical plants in a phylogenetic
context. In the case of Byttneria and Ayenia, changes
in growth form coincide with radiations into new geographical areas
and habitats.
Key words: Ayenia, Byttneria, Malvaceae, Sterculiaceae