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Phylogeny of Chamaecrista ser. Coriaceae (Leguminosae) Unveils a Lineage Recently Diversified in Brazilian Campo Rupestre Vegetation

Premise of research. Chamaecrista sect. Chamaecrista ser. Coriaceae comprises 22 species, mostly distributed in the highlands of Brazil in Cerrado (Neotropical savanna) and Campo Rupestre (upland rocky field) vegetation. Phylogenetic studies for plant taxa of these rich and endemic Brazilian floras are still scarce. In this context, the main objective of our study was to examine the phylogenetic history of a plant group diversified in the mountainous areas of central Brazil. Methodology. The phylogeny of Chamaecrista ser. Coriaceae was examined with combined data from two nuclear regions (ETS [external transcribed spacer] and ITS), two plastid regions (trnD-T and trnL-F), and morphological evidence from comprehensive sampling of the series. We used phylogenetic analyses to evaluate morphological-character evolution to identify putative synapomorphies, and we used Bayesian estimation to explore the timing of diversification of the group. Pivotal results. The series, as currently circumscribed, appears as polyphyletic in all of the analyses, but most of the species ascribed to it form a well-supported clade endemic to highland areas in the Brazilian Cerrado, referred to as the Coriaceae clade. The plastid regions provided high support for the monophyly of this clade, with the nuclear regions providing better resolution within the clade. In addition to molecular evidence, two putative morphological synapomorphies were found. The age-estimation analyses show a recent diversification in the group. Conclusions. Molecular and morphological data indicated that a narrower definition of Chamaecrista ser. Coriaceae as a monophyletic group is required. In addition to two clear deletions in the plastid sequences studied, the presence of a woody underground system and flowers with one stamen displaced to the same side as the gynoecium appear as putative morphological synapomorphies. The low resolution found among species within the clade may reflect a recent radiation that has occurred in the past 5 Myr—a common pattern in other groups restricted to highland areas in South America.