Accurate species delimitation is essential for most areas of research concerning biological organisms. Integration of multiply lines of evidences such as morphological, geographical and molecular data has been proven to be useful in the delimitation of species boundaries. Sibbaldia procumbens is a perennial herb which has a wide distribution area in the alpine region of the northern hemisphere. The S. procumbens complex has a complex history of classification, the boundaries within species are still unclear, this taxonomic uncertainty mainly concerns the local species in Qinghai-Tibet plateau (QTP) and adjacent regions. 

To elucidate the species boundaries, ZHANG huajie, Ph. D from Wuhan Botanical Garden, supervised by Prof. WANG Hengchang, revised exhaustive morphological character based on specimen and abundant fresh samples collected from southeast of China. Ten pairs simple sequence repeats (SSRs) were used to assess the genetic diversity and relationships among accessions collected from different regions at the population level. A total of 246 accessions were tested with SSR markers. 

The result showed all the individuals were classified into 3 clusters. Stable variation in the morphology of leaflets, epi-sepal and achenes was found between individuals from eastern and western Tibet, and this corresponded to the observed genetic structure when K = 2.

The combined analysis of morphology and SSRs suggests 3 species should be recognized in the complex in China (S. procumbens, S. cuneata and S. aphanopetala). The ranges of these 3 species are mostly geographically separate from each other. S. procumbens has a circumpolar distribution with a center diversity in Europe and North America, whereas S. aphanopetala (Handel-Mazzetti) has narrow distribution which concentrated in the Hengduan mountains of China, where the microenvironment is heterogeneous, which often leads to intra-specific divergence. S. aphanopetala has often been treated as a variety of S. procumbens, but here they restore it to species rank. S. cuneata (Hornem.ex Ktze) has a wider distribution which distributed in Qinghai-Tibet plateau and extends to Europe Mediterranea floristic region.  

This study was supported by National Natural Science Foundation of China, and results were published in the Botanical Journal of the Linnean Society entitled “Circumscription of the Sibbaldia procumbens complex (Potentilleae: Rosaceae) in China based on evidence from simple sequence repeat markers and morphology”  

STRUCTURE analysis of 246 individuals of the Sibbaldia procumbens complex. (Image by ZHANG Huajie)