Abstract: The ITS of ribosomal DNA was sequenced to investigate the difference between ITS sequences for 13 populations of Opisthopappus taihangensis（8 populations）and O. longilobus（5 populations）of Opisthopappus. The results indicated that the total length of ITS was 682 bp containing 15 parsimony informative sites. Eighteen nrDNA haplotypes were identified. High haplotype diversity and nucleotide diversity had occurred into O. taihangensis（hd = 0.558，πd = 0.00158）and O. longilobus populations（hd = 0.908，πd = 0.00537）. Some haplotypes were unique ones for O. taihangensis and O. longilobus respectively，some were shared by this two species. All indentified haplotypes clustered into two lineages，Hn8 might be an ancestral haplotype for the lineageⅠ，Hn1 was the predominant and widespread one in the cladeⅡ. The all studied populations of O. taihangensis and O. longilobus was gathered a monophyletic clade. Five O. longilobus populations were not gathered together，LLS and SBY of O. longilobus were gathered together with all eight O. taihangensis populations which indicated exchange of genes or interspecific hybridization occurred between O. taihangensis and O. longilobus.During the process of evolution，long-distance dispersal and colonization may be a major historical event for O. longilobus；A pattern of population expansion and re-colonization was observed in O. taihangensis before the uplift of Taihang Mountains.

Key words: Opisthopappus taihangensis, O. longilobus, ribosomal DNA, ITS