Phylogeography of <i>Bistorta plumosa</i>, an amphi-Beringian Arctic herb with high genetic variation

The geographic origins of the present-day Arctic flora are complex. Studies of genetic structure provide valuable insights, but remain based on too few species. The Bistorta officinalis complex, poorly known but widely distributed in both alpine and Arctic regions of the Northern Hemisphere, includes the Arctic tundra species Bistorta plumosa (Small) Greene in northwestern North America and eastern Asia. We sequenced two plastid DNA regions in 73 samples of B. plumosa and related species from Yukon, Alaska, and Russia, performed Bayesian phylogenetic analysis, and analyzed phylogeographic variation in B. plumosa. We show that B. plumosa represents a distinct amphi-Beringian lineage within the B. officinalis complex. We identified strikingly high genetic diversity within B. plumosa, higher than in most Beringian plant species that have been studied and similar to other species with a long history of persistence in Arctic habitats. The current geographic range of B. plumosa is restricted mostly to unglaciated areas but has high levels of genetic diversity in all parts of the sampled range, indicating little range shift at least since the Last Glacial Maximum. This contrasts with many Arctic tundra species, and emphasizes the variety in patterns of post-Pleistocene range expansion that can underlie similar geographic ranges.