Phylogeography of Potentilla fruticosa (Rosaceae) in the Qinghai-Tibetan Plateau revisited: a reappraisal and new insights

Background: Most empirical studies to date have suggested that alpine plants in the central Qinghai-Tibetan Plateau (QTP) originated from the south-eastern QTP. However, previous phylogeographcial analysis of Potentilla fruticosa suggested that it diversified in the central QTP, which has also been assumed to have been a glacial refugium, and expanded to the north-eastern regions during the mid-Holocene period. Aim: We reappraise this claim in the light of information acquired from sampling, haplotyping and analysing additional populations. Methods: We sequenced the chloroplast trnT-L intergenic spacer of 346 individuals collected from 52 populations. We reconstructed phylogenetic relationships among haplotypes through Bayesian and Network analysis, and used several methods for demographic analysis. Results: Some common and highly divergent haplotypes were distributed in the central, western and south-eastern QTP. Mismatch and other population genetic analyses applied to our data suggested that a distinct range expansion had occurred between approximately 30,000 and 325,000 years ago (kya). Conclusions: Besides the possible postglacial expansion in the north-eastern QTP, our results further suggested that the range of the species radically expanded across the whole Plateau before the last glacial maximum (around 18 kya) and the south-eastern, western and central QTP regions had together provided important refugia during recent glacial stages. These findings, in contrast to the previous conclusions, highlight the importance of adequate sampling strategies in phylogeographical studies.