Historical biogeography of Florestina (Asteraceae: Bahieae) of dry environments in Mexico: evaluating models and uncertainty in low-diversity clades

Mexican dry environments are widespread and characterized by a rich flora and fauna in terms of both overall species diversity and endemism, but the factors that have shaped this diversity remain unclear. In this study, we evaluated hypotheses concerning the biogeographical origin and evolutionary history of Florestina (Asteraceae) in Mexican dry environments. For this, we generated a time-calibrated phylogenetic tree from the nuclear non-coding external and and internal transcribed spacers (ETS, ITS), using the program BEAST. Based on this phylogenetic tree, we employed the package BioGeoBEARS to infer the historical biogeography of the genus, comparing different biogeographical models and estimating the ancestral range probabilities. Our time-calibrated phylogenetic tree suggested that the genus Florestina diverged during the early Pliocene c. 5.2 Mya and diversification continued throughout the Pleistocene. Furthermore, results suggest that the biogeographical origin of the Hymenothrix/Palafoxia/Florestina clade was in Nearctic regions, not in Neotropical regions as previously suggested. We hypothesize that the ancestor of Florestina became disjunct and isolated in tropical dry forests of southern Mexico from Palafoxia after the rifting of the Baja California peninsula from the Mexican mainland.