The difficulty in clarifying species of genus Ligularia Cass. has been attributed to rapid and continuous allopatric speciation in small and isolated populations, combined with interspecific diploid hybridization in the Qinghai‐Tibetan Plateau and adjacent areas. However, no concrete example has been reported to prove this hypothesis. We studied a natural mixed population of six species of Ligularia in which some individuals were morphologically intermediate between L. subspicata and L. nelumbifolia. Based on DNA sequences (trnC‐F, trnL‐rpL32, trnQ‐5′rps16, trnK‐rps16, and internal transcribed spacer) and inter‐simple sequence repeat data, we concluded that putative hybrids are primarily products of hybridization between L. nelumbifolia and L. subspicata. The other four species or additional, unknown species may also be involved in hybridization. This hybridization is bidirectional but asymmetrical. Hybrid individuals were mostly the first generation, but F2 and later‐generation hybrids were also present. Moreover, the backcrossed individuals detected indicate that natural gene flow occurs among at least three Ligularia species. Hybrids may become stabilized to form new species or may function as intermediates in evolutionary diversification.

Natural hybridization has been considered to represent an important factor influencing the high diversity of the genus Ligularia Cass. in the Hengduan Mountains, China. Natural hybridization has been confirmed to occur frequently in Ligularia. To date, however, it has been demonstrated only within a single population. In this paper, we present evidence of natural hybridization in Ligularia from four different locations. The internal transcribed spacer (ITS) region of the nuclear ribosomal DNA and three chloroplast intergenic spacers (trnK-rps16, trnL-rpl32 and trnQ-5'rps16) of 149 accessions of putative hybrids and their putative parents (L. cymbulifera and L. tongolensis) were analyzed for evidence of hybridization. The ITS data clearly distinguished two putative parental species and sympatric L. vellerea and supported the hypothesis that those morphological intermediates were products of natural hybridization between L. cymbulifera and L. tongolensis. Moreover, several identified morphological parents were actual introgressed products. Because of hybridization and introgression, chloroplast DNA sequences generated a poorly resolved network. The present results indicate that varying degrees of hybridization and introgression occur differently depending on the habitat context. We conclude that gene flow caused by natural hybridization in Ligularia indeed plays an important role in the species diversity.