From Rainforests to Open‐Vegetation: The Biogeographic History of <i>Chamaecrista</i> (Leguminosae) in the Neotropics

ABSTRACT Aim We reconstructed the biogeographical history of a species‐rich legume genus by testing alternative hypotheses on the origin and expansion of neotropical open‐vegetation areas, with particular emphasis on the campos rupestres . Location Neotropics. Taxon Chamaecrista (Leguminosae), one of the most speciose genera of the neotropical region. Methods We reconstructed a fossil‐calibrated phylogeny of Chamaecrista species and built a comprehensive database of species occurrences. We fitted and compared nine biogeographic models that differed in area availability and dispersal rates across time frames. These time frames were defined based on major climatic processes that have influenced neotropical open‐vegetation areas. Results and Main Conclusions Under the best‐fitting biogeographical model, Chamaecrista originated in the Amazon during the Mid Eocene. A single ancestral Chamaecrista lineage colonised the campos rupestres before the Late Oligocene–Mid Miocene, when climatic shifts presumably expanded lowland open‐vegetation areas in the Neotropics. Most diversification of Chamaecrista species occurred in the campos rupestres from the Late Miocene to the Quaternary. Multiple ancestral Chamaecrista lineages dispersed from the campos rupestres to the Cerrado from the Mid Miocene onwards, while few lineages dispersed into the Caatinga during the same period. We propose that the campos rupestres might have functioned as a montane reservoir of plant diversity, harbouring lineages that later dispersed into adjacent lowland areas.