Evolutionary Histories of and .

The genus is widely distributed, primarily in East Asia. is located at the northern limit of this genus distribution, and understanding changes in its distribution is crucial for understanding the evolution of plants in this region, as well as their relationship with geological history and climate change. Moreover, the classification of sect. in Japan has not been clarified. Therefore, this study aims to understand the evolutionary history of the Japanese sect. . The genetic population structure was analysed using SNP data and MIG-seq. The relationship between the Japanese sect. , including the related species in China, was further inferred from the phylogeny generated by RA x ML, SplitsTree and PCA. Population genetic structure was inferred using a Bayesian clustering method (ADMIXTURE). We subsequently employed approximate Bayesian computation, which was further supported by the coalescent simulations (DIYABC, fastsimcoal and Bayesian Skyline Plots) to explore the changes in population, determining which events appropriately explain the phylogeographical signature. Ecological niche modelling was combined with genetic analyses to compare current and past distributions. The analyses consistently showed that and are distinct, having diverged from each other during the Middle to Late Miocene period. Furthermore, differentiated into four major populations (North, South, Ryukyu-Taiwan and Continent). The Japanese sect. underwent speciation during archipelago formation, reflecting its ancient evolutionary history compared with other native Japanese plants. did not diverge from in snow-rich environments during the Quaternary period. Our results suggest that both species have been independent since ancient times and that ancestral populations of have persisted in northern regions. Furthermore, the population on the continent is hypothesised to have experienced a reverse-colonisation event from southern Japan during the late Pleistocene glaciation.