XVI International Botanical Congess

Previous phylogenetic analyses of the order Malvales suggested a basal lineage of four tribes of Sterculiaceae (Byttnerieae, Theobromeae, Lasiopetaleae and Hermannieae), although exact relationships among them were unclear. Here we analyze sequences of the chloroplast gene ndhF for 35 species of these Byttnerioideae." The monophyly of this diverse group is supported with the inclusion of Kleinhovia from a fifth tribe. Only the Hermannieae is monophyletic. These results have strong implications for petal and stamen evolution. The unusual cup-shaped petals of the Byttnerieae (e.g. Theobroma cacao) are plesiomorphic in the Byttnerioideae with transitions to large, flat petals and small, scale-like petals. Stamen number and the presence of staminodes have been used to distinguish the tribes. However, our analyses indicate that these characters show extensive homoplasy.