Historical migration and taxonomic entity of Korean endemic shrub Lespedeza maritima (Fabaceae) based on microsatellite loci

Various plant species are endemic to the Korean Peninsula, but their evolutionary divergence and establishment are poorly understood. One of these, Lespedeza maritima, has been proposed as either a hybrid (L. cyrtobotrya × L. maximowiczii) or a synonym of L. thunbergii. A distinct taxon, L. uekii, has been proposed for inland populations. We investigated genetic diversity and structure in L. maritima and related taxa to resolve this. Genotypes of L. maritima (n = 244, including L. uekii) were determined using 12 microsatellite loci, then compared with those of related species. Genetic diversity within L. maritima was estimated, and Bayesian clustering analysis was used to represent its genetic structure and that of related taxa. Its distribution during the last glacial maximum (LGM) was predicted using ecological niche modelling (ENM). Neighbour-joining (NJ) analysis and principal coordinate analysis (PCoA) were used to investigate relationships among species. Bayesian tree based on nuclear ribosomal internal transcribed spacers (nrITS) was also reconstructed to show relationships and divergence time among species. Morphological features were examined using flower characteristics. In result, expected heterozygosity (H(E)) and allelic richness (A(R)) within L. maritima were higher in southern than northern populations. Bayesian clustering analysis largely assigned populations to two clusters (K = 2) (south vs. north). The ENM showed that L. maritima occurred around the East China Sea and Korean Strait land bridge during the LGM. Compared with other Lespedeza species, L. maritima was assigned to an independent cluster (K = 2–5), supported by the NJ, PCoA, Bayesian tree and morphological examination results. Lespedeza maritima and L. uekii were clustered to one clade on Bayesian tree. Given results, current L. maritima populations derive from post-LGM colonization away from southern refugia. The type L. uekii, which grows inland, is thought synonym of L. maritima. In addition, L. maritima is considered a distinct species, compared with related taxa.