Secondary contact, hybridization and polyploidization add to the biodiversity in the Hengduan Mountains, exemplified by the widespread Corallodiscus lanuginosus (Gesneriaceae)

Corallodiscus lanuginosus is distributed 12,000 km across its northeast–southwest boundaries, showing its highest morphological diversity in the Hengduan Mountains, Southwest China. We investigated the mechanisms behind the high diversity in this species. We acquired ITS sequence data across the distribution range of the genus, reconstructed dated phylogenies, projected the resulting clades onto geographic maps and linked the results with inferred ploidy levels of the populations. We found strong geographic patterns for the ITS clades but with extensively overlapping ranges, particularly in the Hengduan Mountains area. We deduced an origin of C. lanuginosus in the mid-Oligocene. We used the presence of ITS polymorphisms to infer a high level of hybridization events mainly in areas of clade overlap, where we also inferred repeated tetraploidization events to have taken place. Pre- and post-Quaternary climate oscillation-driven expansions and contractions of distribution ranges have allowed secondary contacts, hybridization and introgression that shaped the current patchy distribution of morphological diversity in the species. Polyploidization as a reinforcing genetic barrier added to the genetic diversity in space and time particularly in the Hengduan Mountains.