A new infrageneric classification of the pantropical genus Chamaecrista (Fabaceae: Caesalpinioideae) based on a comprehensive molecular phylogenetic analysis and morphology

Abstract

Chamaecrista with > 330 species, six sections, three subsections and 39 series has had a long and complex taxonomic history. The genus is monophyletic, but most of its traditional infrageneric categories are not. To test the monophyly of sections, subsections and series of Chamaecrista, we used two molecular phylogenetic approaches. The first (Broad) based on two DNA regions (ITS and trnL-F) includes a comprehensive sampling of Chamaecrista spp. and infrageneric taxa. The second (Multilocus) is based on four molecular regions (ITS, ETS, trnL-F and trnE-T) for a smaller but representative sampling. We performed ancestral character reconstructions to identify morphological characters that could serve as synapomorphies for major clades. Both molecular approaches support Chamaecrista and sections Apoucouita, Grimaldia and Xerocalyx as monophyletic, but sections Chamaecrista, Caliciopsis and Absus and most of the series are not monophyletic. The four main clades recovered are all characterized by a combination of morphological characters: a clade of tree species with cauliflorous inflorescences (including species of section Apoucouita); a mostly Brazilian campo rupestre clade (including all species of subsections Adenophyllum, Baseophyllum and Otophyllum); a clade of mostly herbaceous/shrubby species with solitary flowers or fascicles (including sections Chamaecrista, Caliciopsis and Xerocalyx and extra-American species) and a clade (with three main subclades) of species with viscous indumentum (including section Grimaldia and section Absus subsection Absus). We propose a new infrageneric classification for Chamaecrista supported by molecular phylogenetic analyses and morphology, recognizing the four main clades as sections Apoucouita, Baseophyllum, Chamaecrista and Absus, the last with three subsections (Absus, Viscosa and Zygophyllum), but we do not recognize any previously circumscribed series. Our taxonomic treatment includes descriptions of and a key to the newly defined infrageneric taxa and an updated species list for the genus under the new classification.