Molecular evidence for natural hybridization between Ligularia nelumbifolia and Cremanthodium stenoglossum (Asteraceae, Senecioneae)

Natural hybridization occurred frequently in the sunflower family. To date, however, no study on natural hybridization involving in Ligularia and Cremanthodium has been reported. Here, we presented the molecular evidence for natural hybridization between Ligularia nelumbifolia (Bureau & Franch.) Hand.-Mazz. and Cremanthodium stenoglossum Ling & S.W.Liu. Four nuclear DNA regions were sequenced to test the natural hybridization hypothesis, and three chloroplast DNA regions were sequenced to determine the direction of hybridization. Analyses of the investigated DNA data suggested that all of the putative hybrid individuals were derived from hybridization between L. nelumbifolia and C. stenoglossum and that bidirectional hybridization occurred. Moreover, sympatric Ligularia tsangchanensis (Franch.) Hand.-Mazz. and Ligularia virgaurea (Maxim.) Mattf. ex Rehder & Kobuski were not apparently involved in the hybridization. Although NewHybrids analysis showed that all the putative hybrid individuals were F-1 class, a low frequency of backcrossing to C. stenoglossum might exist in the hybrid swarm. In such a case, hybrids might serve as a bridge facilitating gene flow between L. nelumbifolia and C. stenoglossum, and hybrid speciation is unlikely to happen for these hybrid individuals without asexual reproduction. Given the poorly resolved phylogenetic relationship between Ligularia and Cremanthodium, the occurrence of natural hybridization between L. nelumbifolia and C. stenoglossum might provide new insights into the recircumscription and redelimitation of these two genera.