Molecular markers provide evidence for a broad-fronted recolonisation of the widespread calcareous grassland species Sanguisorba minor from southern and cryptic northern refugia.

Calcareous grasslands belong to the most species-rich and endangered habitats in Europe. However, little is known about the origin of the species typically occurring in these grasslands. In this study we analysed the glacial and post-glacial history of Sanguisorba minor, a typical plant species frequently occurring in calcareous grasslands. The study comprised 38 populations throughout the whole distribution range of the species across Europe. We used molecular markers (AFLP) and applied Bayesian cluster analysis as well as spatial principal components analysis (sPCA) to identify glacial refugia and post-glacial migration routes to Central Europe. Our study revealed significant differences in the level of genetic variation and the occurrence of rare fragments within populations of S. minor and a distinct separation of eastern and western lineages. The analyses uncovered traditional southern but also cryptic northern refugia and point towards a broad fronted post-glacial recolonisation. Based on these results we postulate that incomplete lineage sorting may have contributed to the detected pattern of genetic variation and that S. minor recolonised Central Europe post-glacially from Iberia and northern glacial refugia in France, Belgium or Germany. Our results highlight the importance of refugial areas for the conservation of intraspecific variation in calcareous grassland species.