Premise: The formation of isolated montane geography on islands promotes evolution, speciation and followed radiation with ecological changes. Thus, investigating evolutionary history of montane species and associated ecological changes may help efforts to understand how endemism formed in islands’ montane floras. To explore this process, we investigated the evolutionary history of the Rhododendron tschonoskii alliance, which grows in montane environments of the Japanese Archipelago and Korean Peninsula.

Methods: We studied the five species of the R. tschonoskii alliance and 30 outgroup species, using genome-wide single nucleotide polymorphisms and cpDNA sequences, in association with environmental analyses.

Results: The monophyletic R. tschonoskii alliance diverged since the late Miocene, and its cold climatic niche largely differentiated from those of outgroup species. We observed clear genetic and niche differentiations between the taxa of the alliance.

Conclusions: The association of the evolution of the alliance with formation of cooler climates on mountains indicates that it was driven by global cooling since the mid-Miocene and rapid uplift of mountains since the Pliocene. The combination of geographic and climatic isolations promoted high genetic differentiation between taxa, which has been maintained by climatic oscillations since the Quaternary.

Please read the README document ("README.md") and the accompanying published article: Yoichi W, Tamaki I, Oh S-H, Nagano AJ, Uehara K, Tomaru N, Abe H. 2023. The evolutionary history of rice azaleas (Rhododendron tschonoskii alliance) involved niche evolution to a montane environment. American Journal of Botany. https://doi.org/10.1002/ajb2.16166