Geographical barrier and Quaternary climate change promoted allopatric divergence and disjunct geographic distribution in an endemic and vulnerable species (<i>Morella adenophora</i>) on the continental island of South China

Abstract Hainan Island and Taiwan Island are two well-known continental shelf islands, but few studies have explored their biogeographic relationships with the adjacent Chinese mainland. To explore their biogeographic patterns, nine SSR markers, five chloroplast DNA markers, and one nuclear ribosomal DNA (nrDNA) marker (ITS) were used to analyse the inheritance of Morella adenophora (Hance) J. Herb., an endemic, vulnerable species. Niche modelling, Bayesian skyline plot, Reconstruct Ancestral State in Phylogenies, and phylogenetic analyses were also used to investigate the geographic structure and evolutionary history of this continental shelf island system. Our results revealed that M. adenophora comprises two groups: M. adenophora var. adenophora, which is distributed in mainland China and Hainan Island, and M. adenophora var. kusanoi, which is endemic to Taiwan Island. These two groups show no shared haplotypes and exhibit clear phylogeographic structure. In addition, the long-distance geographical barriers and climate change were the main factors contributing to the formation of M. adenophora var. kusanoi. Overall, our findings highlight the importance of geographic barriers and Quaternary climate fluctuations in shaping the genetic structure and biogeographic patterns of M. adenophora. This study contributes valuable insight into the evolutionary history of species on continental shelf islands.