Distribution of genetic variation over time and space is relevant to demographic histories, and tightly linked to ecological disturbances as well as evolutionary potential of an organism. Therefore, understanding the pattern of genetic diversity is a primary step in conservation and management projects for rare and threatened plant species. We used 8 microsatellite markers to examine the level of genetic diversity, spatial structure and demographic history of Plagiorhegma dubium, a rare myrmecochorous herb, populations sampled across northeast Asia and Siberia. We found low within-population genetic variation associated with historical bottlenecks. Although pairwise FST values were not much higher than the ones found in similar life form species, STRUCTURE and PCoA revealed a clear broad-scale spatial pattern of genetic structure. Bayesian clustering (best K=6) and PCoA identified three populations that are distinctive from neighboring populations in the Korean peninsula, which suggests potential units for conservation and management plans in Korea. MIGRATE-N and BAYESASS showed that both contemporary (0.003-0.045) and historical migration rates (2e-5-4.6e-4) were low. Our findings provide a good example, where genetic considerations should be integrated for conservation and management plans of rare and threatened species.