Patterns of genomic variation and population structure suggest the strong influence of allopatry between peninsular and island distributions of seashore spatulate aster on the Korean east coast region.

The long and varied coastline of the Korean Peninsula is home to plants that thrive in the transition zone between terrestrial and marine ecosystems. The Korean east coast, and the volcanic island of Ulleungdo facing it, is a region where species populations and lineages are allopatrically distributed, including those of the seashore spatulate aster (Aster spathulifolius Maxim.). In this study, we examined the disjunct distribution of this coastal specialist by employing genome-wide SNP markers to evaluate its genomic diversity and structure, and infer its number of independently evolving lineages in this region. Our findings suggest that the genetically distinct population structure between the peninsular and island distributions, and the significantly reduced genetic variation patterns, more so for the insular populations, appeared to be the classic signatures of the mainland-island model. The vicariant population distribution was further found to be delineated by a genetic barrier, i.e., the East Sea geographic break, although isolation by distance may have also influenced the divide. Along with the molecular line of evidence, the nomenclatural and taxonomic implications of the findings are also discussed in this paper.