Trichophorum planifolium, like many Canadian species-at-risk, reaches the northern extent of its range in Canada, but is common farther south in the United States. Peripheral populations may be important sources of adaptive and evolutionary potential, possessing unique genetic diversity and/or adaptations to local conditions. However, such populations are typically small and isolated and may therefore be susceptible to extinction. Using microsatellite markers, we compared the level and spatial distribution of genetic diversity and environmental characteristics between the Canadian and American populations of T. planifolium. Overall, low diversity and high inbreeding were detected, with all populations exhibiting comparable levels. This suggests inbreeding depression is not limiting recruitment in the Canadian population, as previously hypothesized. We also found high differentiation between populations and unique environmental conditions at the northern range margin. Consequently, efforts to bolster genetic diversity in the Canadian population are not presently warranted and should be avoided in the future.