ABSTRACT Background Lepidagathis Willd. (Barlerieae, Acanthoideae, Acanthaceae) is a pantropical plant genus with about 156 species. Classification of Lepidagathis and Lophostachys has been under debate for long. The genus is mainly Asian in distribution, followed by Africa, with an odd distribution of over a quarter of its diversity in the Neotropics. Aims Given its pantropical distribution, we hypothesised that this pattern may be due to long distance dispersal followed by radiation in either the Old World or New World. Therefore, we aimed to test the monophyly of the Old World and New World species and trace its ancestral area using molecular dating and biogeographical analysis. Materials and Methods We used 28 Lepidagathis sensu lato (s.l.) species, with seven molecular markers (ITS, trnL‐LF , trnSG , trnGR , psbA‐trnH , rps16 and rbcL ), and conducted single‐gene phylogenies. Later, we used a concatenated dataset of five markers (ITS, trnL‐LF , trnSG , trnGR and rps16 ) to perform molecular dating based on secondary calibration as well as primary calibration. For historical biogeography, we applied two schemes: one treating peninsular India—home to about 35 species—as a distinct region, and another grouping it with Southeast Asia. Results Our study of the 28 species resolved Lepidagathis into three well‐supported clades and supported its broad circumscription ( sensu lato ), including the former Lophostachys . The combined gene phylogeny places the African monotypic genus Schaueriopsis variabilis and the Asian genus Chroesthes within Lepidagathis s.l . Historical biogeography under the DIVALIKE+J model identified Africa as the most likely ancestral area for the genus, with Indian endemic species derived from Neotropical ancestors. In an alternative scheme, which included India within Asia, it was inferred that Lepidagathis s.l . has evolved from Asia, with all three lineages within Lepidagathis s.l . also with Asian ancestry. Discussion The timing of the dispersal events out of Africa into the neotropics, and dispersal into the paleotropics, was during the late Oligocene, suggesting that it must have been long‐distance dispersal, as there were no land bridges connecting the Americas with the Old World. Conclusion This phylogenetic study, together with the biogeographical analysis demonstrates that Lepidagathis and Lophostachys represent independently evolving lineages that can be recognised as distinct subgenera. Moreover, Lepidagathis s.l . provides strong evidence for long‐distance intercontinental dispersal events, inferred to have occurred during the late Oligocene. Our biogeographical analysis, along with the genus's greatest species diversity in Asia, supports an Asian origin for Lepidagathis as the more plausible scenario.
Surveswaran et al. (Sun,) studied this question.