LAUSR

Rheum tanguticum (Polygonaceae), an endangered traditional Chinese and Tibetan medicines, is distributed in the Tibetan Plateau. To investigate endangered reasons and protect the wild resources, we collected 87 individuals fromnine populations of R. tanguticum, and estimated the genetic diversity of this speciesbased on the cpDNAtrnS⁃G region. The results showed that there was high genetic diversity within this species. The length of the total trnS⁃G region of the 87 individuals ranged from 944 to 954bp, and covered 965 nucleotide positions after being aligned. Variations were detected in 23 nucleotides, including 13 nucleotide substitutions and 10 indel sites. On the basis of these nucleotide mutations, a total of four nucleotide haplotypes (H1—H4) were identified. The development of a parsimony network showed that the four haplotypes made up a shallow star genetic tree. Haplotypes H1, H2, and H4 were located at the tips of the network, representing recent haplotypes.Haplotype H3 and three missing haplotypes were in the center of the star network.Moreover, since haplotype H3 had the highest frequency, it was identified as an ancestral haplotype.The total diversity (Ht) among the individuals collected was 0. 694, indicating a high genetic diversity. In addition, a high level of population differentiation was observed (GST = 0.960), as determined by PERMUT analysis, showing 95.97% genetic differentiation between populations, whereas the remainder of the total genetic variation ( 4. 03%) was attributed to within⁃population htt p:/ /w ww .ec olo gic a.c n http: / / www.ecologica.cn diversity (Hs= 0.028). AMOVA analysis (FST = 0.9631) also indicated that the genetic diversity among populations was greater than that within populations. The value for gene flow was fairly low (Nm = 0.01), indicating a limited gene flow between populations, which is consistent with the findings of PERMUT and AMOVA analysis.The NJ tree of populations based on genetic distance revealed three supported groups. However, populations with close geographic distance did not cluster together, indicating that there was no direct relationship between the geographic distances and genetic distances of the nine populations, which was confirmed by the Mantel test( r = 0.2461, p = 0.2060). The high genetic diversity of the examined populations is probably associated with the long evolutionary history and life history of R. tanguticum.The large genetic differentiation between populations might be related tothe alpine geographical environment and human activity. Therefore, we suggest that more wild populations with high genetic diversity should be protected by an in⁃situ conservation program at sites distant from human activity. We also recommend the collection and conservation of seeds from populations with rich genetic diversity for the ex⁃situ conservation of genetic stocks and their propagation. These conservation measures will certainly provide the basic resources required to increase the number of populations of this species and extend its range of distribution.