Conservation genetics of Pitcher's thistle (Cirsium pitcheri), an endangered Great Lakes endemic

Pitcher's thistle (Cirsium pitcheri Torr. ex Eaton (Torr. & Gray)) is a Great Lakes endemic that in Canada is designated as threatened at both the provincial (Ontario) and national levels. Management plans will benefit from conservation genetic data, which can provide insight into population genetic diversity and differentiation. We obtained genetic data from nuclear and chloroplast microsatellite markers from 17 populations of C. pitcheri around the Great Lakes. The nuclear data revealed overall low levels of diversity, high levels of inbreeding, and low levels of population connectivity. The chloroplast data identified a single haplotype, which is consistent with reduced genetic diversity following postglacial colonization. The high levels of inbreeding within populations will likely pose a serious threat to populations in the short term ; these have resulted from a combination of low connectivity between populations, and small and fluctuating population sizes. Future management of C. pitcheri populations should consider human-mediated dispersal of plants or seeds among sites.