Chloroplast DNA phylogeography ofRhodiola alsia(Crassulaceae) in the Qinghai–Tibet Plateau

Abstract

We studied the phylogeography of Rhodiola alsia (Fröderström) S.H. Fu, which is a perennial herbaceous plant endemic to the Qinghai–Tibet (Q–T) Plateau, by sequencing one intergenic chloroplast spacer, rpl20–rps12 (844 bp). The sampling design included 18 populations and 315 individuals, and spanned the entire distribution range of the species. Thirty-one haplotypes were characterized, and polymorphism was observed both within and among populations. Most haplotypes were restricted to single sites or to neighbouring populations, suggesting an extremely low level of long distance gene flow via seeds. Only three haplotypes were common and widespread throughout the distributional range of R. alsia. The present geographical distribution of haplotypes probably reflects an ancient geographical pattern between the platform and southeastern margin of the Q–T Plateau identified as genetic hotspot areas. We suggest that populations of R. alsia survived in isolated refugia located in the platform and the southeastern margin of the Q–T Plateau during the Quaternary glaciation, at least during the last glaciation maximum (LGM, 32 000–16 000 years ago). The populations of R. alsia were geographically isolated by a subsequent local range expansion and independent evolution. The genetic structure of R. alsia is very different from previous phylogeographical studies of Q–T Plateau alpine plants and illustrates the importance of species-specific characteristics such as distribution areas and life-history traits which are mainly responsible for different patterns of genetic variation. Our investigation thus provides a new pattern of several refugia on the plateau platform.