Phylogenomics reveals distinct evolutionary lineages of Japanese Cinnamomum species in the Nansei Islands

Although Cinnamomum includes globally important spice and medicinal plants, genome-scale knowledge of Cinnamomum species native to Japan remains limited. The Nansei Islands are an approximately 1,200-km-long archipelago located between the Pacific Ocean and the East China Sea and represent a key biogeographic region shaped by deep-sea barriers such as the Tokara and Kerama Gaps. Here, we integrated chloroplast and nuclear genome data generated in this study with public datasets to examine the phylogenetic relationships of four Cinnamomum species native to the Nansei Islands and ten related species. Chloroplast genomes showed no major structural differences among the four island species, whereas nuclear genome data resolved two distinct evolutionary lineages in the Nansei Islands: C. yabunikkei, C. x durifruticeticola, and C. daphnoides formed a distinct Nansei Islands lineage separate from Sri Lankan, Indonesian, and Taiwanese lineages, whereas C. sieboldii was placed in a Taiwanese lineage. Ancestry estimation indicated that C. x durifruticeticola and C. daphnoides share a common ancestral component, while C. sieboldii exhibited a single homogeneous ancestral component, suggesting reduced ancestral diversity after divergence from a Taiwanese lineage. These findings reveal previously unrecognized genomic differentiation among Japanese Cinnamomum species and suggest that deep-sea barriers, dispersal, and long-term isolation shaped their diversification.