Phylogenetic and molecular dating analyses of Catasetum (Orchidaceae) indicate a recent origin and artificial subgeneric groups

Catasetum species have an intriguing mechanism of pollinarium ejection after a mechanical stimulus of the column extensions, the antennae, of staminate flowers. The subgeneric classification of Catasetum is based on antenna morphology, although the subgenera have not been tested phylogenetically yet. With this in view, our goal was to test the monophyly of the subgeneric groups through a maximum likelihood approach with representatives of all groups of Catasetum, for which two nuclear and four plastid regions were sequenced and combined. Divergence times were estimated under an uncorrelated lognormal relaxed clock model, and nodes were calibrated using previous estimates. As a result, all subgeneric groups are non-monophyletic, and antenna morphology possibly does not reflect the evolutionary history of Catasetum, even though it is related to sexual reproduction in the genus. The very short branches in the Catasetum clade indicate a relatively recent origin of the genus, estimated between the Late Miocene and Pliocene. The low support in internal nodes could be due to past hybridisation events or due to incomplete lineage sorting. We suggest that Catasetum had a wide ancestral geographic distribution, and we detected two main dispersal events. One was the diversification of the clade from the Mesoamerican and Pacific areas. Later recolonisation events of these areas from Amazonian ancestors indicate that the Andes are not a barrier to dispersal for the genus. The second main dispersal event marked the occupancy of the Atlantic Forest by Amazonian ancestors, which supports hypotheses of past connections between the Amazonian and the Atlantic forests after the Dry-Diagonal formation.