Phylogeny of Chamaecrista Moench (Leguminosae­Caesalpinioideae) based on nuclear and chloroplast DNA regions

Chamaecrista Moench is a genus of caesalpinioid legumes with about 330 species mostly from the New World. The phylogeny of the genus was studied using sequence data from nuclear ITS and plastid trnL-F DNA spacers, representing all six sections of Chamaecrista. Separate and combined analyses recovered the same major clades with high bootstrap and posterior probabilities support, except for the subclades of representatives of sections Caliciopsis, Chamaecrista, and Xerocalyx. The monophyly of Chamaecrista was highly supported in all analyses. Sections Apoucouita and Xerocalyx were supported as monophyletic, sect. Absus was paraphyletic and subsect. Baseophyllum was resolved more closely related to species of sections Chamaecrista, Caliciopsis, and Xerocalyx than to subsect. Absus. The monotypic section Grimaldia was embedded within subsect. Absus. Section Chamaecrista was paraphyletic with respect to sections Caliciopsis and Xerocalyx. Our analyses suggest that the diversification patterns in Chamaecrista occurred through an initial shift from rainforest trees to a more diverse clade of savannah shrubs. Within the latter group, two main subclades were recovered: (1) a planaltine and high-mountain clade characterized by absence of extrafloral nectaries and the appearance of sticky glandular hairs; and (2) a mostly herbaceous clade with axillary fascicled inflorescences and reduced chromosome numbers. This last group is more diverse in open grassland areas and includes many colonizers of waste ground.