Molecular evolution of the leguminosae: Phylogeny of the three subfamilies based on rbcL-sequences

Abstract

The rbcL gene of 49 species (37 genera, 24 tribes of the Leguminosae and two species of the Polygalaceae) was amplified by polymerase chain reaction (PCR) and sequenced directly. rbcL sequences were evaluated with character state (Maximum Parsimony) and distance methods (Neighbour-Joining). The traditional classification of Leguminosae, especially in case of the basal groups, was assumed to be based on apparently ancestral or derived features. Analyses of molecular data show that such seemingly ‘old’ taxa, i.e. Cercideae, Gleditsia, Gymnocladus and Ceratonia, form distinct evolutionary lines, but not necessarily basal groups of the Leguminosae. Using Polygalaceae as an outgroup, the analysis of rbcL sequences showed that the tribes Detarieae/Amherstieae and Cercideae appear to have diverged earlier than the remaining tribes of Caesalpinioideae and might deserve a subfamily rank. The next groups to separate were the sister groups of Caesalpinieae/Cassieae and Papilionoideae. The closely interconnected Caesalpinieae/Cassieae complex forms the base of the Mimosoideae. Papilionoideae and Mimosoideae are monophyletic. Caesalpinioideae is paraphyletic to the other subfamilies, and the classical division of Leguminosae into three subfamilies is not supported. Within Papilionoideae, molecular data indicate that the tribe Sophoreae (and even the genus Sophora) is a heterogeneous collection of species that needs a comprehensive revision.