Phylogenetic relationships and floral evolution of the Byttnerioideae ("Sterculiaceae" or Malvaceae s.l.) based on sequences of the chloroplast gene,ndhF

Previous studies of the Malvales have shown that the Sterculiaceae are not monophyletic. However, members of four traditionally recognized tribes of S terculiaceae (Byttnertieae, Theobromeae, Hermannieae, Lasiopetaleae) appear to constitute a clade named Byttnerioideae. Here we analyze sequences of t he chloroplast gene ndhF for 37 species of Byttnerioideae. The monophyly of this diverse group of plants is supported with the inclusion of Kleinhovia from a fifth tribe of Sterculiaceae (Helictereae). The Hermannieae is the only tribe that appears to be monophyletic as traditionally circumscribed. Rulingia and Commersonia, two genera formerly placed in the Byttnerieae, ar e in a clade with all members of the Lasiopetaleae, The remaining Byttnerie ae, Theobromeae, and Kleinhovia form two clades at the base of the Byttneri oideae. These results imply that the unusual hooded petals of many Byttneri oideae (e.g., Theobroma cacao) are plesiomorphic for the clade, with subseq uent transitions to large, flat petals or small, scale-like petals that lac k a distinct hood. Stamen number has traditionally been used to distinguish tribes in the Sterculiaceae. However, our analyses indicate that this char acter shows extensive homoplasy, with both increases and decreases in stame n number occurring within the Byttnerioideae.