Phylogeographical patterns match the floristic subdivisions: the diversification history of a widespread herb in...

Subtropical China is dominated by evergreen broad-leaved forests (EBLFs) and is acknowledged as a critical region for its high floristic richness and endemism. Our understanding of the evolutionary mechanisms of such global biodiversity hotspots comes almost exclusively from long-lived tree species. Herbaceous plants represent critical biodiversity components in forests, but the diversification history of understorey herbs in subtropical EBLFs remain poorly understood. Here, we investigated the phylogeographical patterns and demographic history of Oreocharis auricula, a widespread perennial herb endemic to the EBLFs of subtropical China.

Both chloroplast DNA sequences and single-copy nuclear genes were used to investigate the genetic variation among 657 individuals from 68 populations. Evidence from molecular dating, demographic history construction and species distribution modelling was also combined to infer the phylogeography and evolutionary history of O. auricula.

Strong phylogeographical signals have been congruently observed using nuclear and plastid DNA markers, with the diversification patterns generally consistent with the recognized floristic subdivisions of subtropical China. Notably, we revealed an important phylogeographical barrier along the Nanling mountain range, which is also around a climatic transition at 24-26°N latitude in subtropical China, separating the south monsoon subtropical EBLFs from the mid-subtropical EBLFs. Demographic expansion and significant niche divergence were detected among the extant lineages, which may have diverged during the early Pleistocene.

The inherent characteristics of understorey herbs with limited dispersal and short generation time intensify the genetic divergence response of O. auricula to abiotic forces, contributing to the profound phylogeographical imprints of mountains and climate in such herbaceous flora. To further substantiate the generality of the identified patterns, it is paramount to extend phylogeographical investigations to other understorey herbaceous taxa in subtropical China. These results have expanded our understanding of the diversification processes of subtropical forests in China.