The genus Bauhinia s.l. (Leguminosae): a phylogeny based on the plastid trnL-trnF region

As the largest genus in tribe Cercideae, the pantropical genus Bauhinia has been the subject of a number of regional treatments in which it has been recognized either as a single genus with several subgenera or as several distinct genera. With the aim to better understand the taxon relationships within Bauhinia and between it and related genera, we have sequenced the plastid trnL-trnF region for 85 species, which together are representative of the eight genera recognized within Bauhinia sensu lato by some workers. In addition, representative taxa were verified for the presence or absence of the plastid rpl2 intron, which previous studies indicated might be a marker for specific lineages within Bauhinia s.l. Both Bayesian and parsimony analyses indicate that Bauhinia s.l. is paraphyletic with the monospecific genus Brenierea clustered within it. This genus, usually described as sister to Bauhinia s.l., forms a clade with the genera Piliostigma and Bauhinia sensu stricto. The remaining genera (Gigasiphon, Tylosema, Barklya, Phanera, Lasiobema, and Lysiphyllum) form a second clade sister to the first. All of these segregate genera are monophyletic except for Phanera, which is divided into two lineages comprising the Asian Phanera species together with the genus Lasiobema, and the second comprising the American Phanera species. The relationship between the Brenierea - Bauhinia s. str. - Piliostigma clade, the Gigasiphon-Tylosema-Barklya-Phanera-Lasiobema-Lysiphyllum clade and the genus Griffonia is not well resolved, but Adenolobus is sister to this large monophyletic group and the genus Cercis is sister to all other Cercideae. Preliminary analyses of the rpl2 plastid region also support the Piliostigma - Brenierea - Bauhinia s. str. clade, suggesting a unique loss event of the intron prior to the diversification of this clade.