Impact of calibration points and molecular dating methods lead to different biogeographical scenarios in Vernonieae (Asteraceae)

Abstract The tribe Vernonieae (Asteraceae) comprises ∼1500 species, one of the largest in the family, with a complex evolutionary history. Here, we reconstructed a phylogenetic tree of the tribe using both newly generated and previous data from 466 species and four genetic markers (rpl32, trnL-F, ndhF, and ITS). We explored and assessed the impact of three molecular dating methods (Bayesian, penalized likelihood and RelTime) and two calibration schemes, employing the pairwise Wilcoxon test. RelTime yielded significantly younger divergence times than Bayesian and penalized likelihood in both calibration sets. Thus, methodological choices fundamentally alter the temporal framework and subsequent evolutionary interpretations. Subsequently, biogeographical (BioGeoBEARS) and diversification (BAMM) analyses were conducted. The biogeographical history appears to be divided into two major temporal blocks: from the Oligocene to the Miocene and from the Pliocene to the Holocene. The origin of Vernonieae was traced back to the Ethiopian region ∼27 Mya, near the Oligocene–Miocene transition, with the colonization of the New World driven by long-distance dispersal rather than ancient vicariance. Four shifts in diversification rates were uncovered corresponding to important Neogene environmental changes, such as the Middle Miocene cooling. These findings provide a refined temporal framework, critical for disentangling the drivers of pantropical diversification.