Spatiotemporal evolution of the global species diversity of Rhododendron

Abstract How large cosmopolitan plant genera survived great environmental changes and rediversified remains largely unknown. Here we investigated mechanisms underlying the rediversification of Rhododendron, the largest genus of woody plants in the Northern Hemisphere. Using 3437 orthologous nuclear genes, we reconstructed the first completely resolved and dated phylogeny of Rhododendron. We found that most extant species of Rhododendron originated by Neogene rediversification from Paleogene relicts during southern migration. The geographically uneven rediversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was driven by two main environmental variables, i.e., habitat heterogeneity represented by elevation range and annual precipitation related to the Asian monsoons, and can be explained by leaf functional traits that show strong phylogenetic signals and correspond well with leaf-forms and geographical regions. Our study highlights the importance of integrating phylogenomic and ecological analyses in revealing the spatiotemporal evolution of species-rich cosmopolitan plant genera.