Abstract: A natural hybrid species in Petrocosmea named Longianthera in Yanshan County, Yunnan Province is confirmed for the first time based on molecular and morphological evidence. The character count procedure of the variable characters show that Longianthera populations are characteristic of the intermediate morphological traits between its putative parents Yanshan and Petrocosmea martinii. The nuclear ribosomal internal transcribed spacer region and three chloroplast regions of matK, trnL-F, and trnT-L are sequenced in the putative hybrid and the related species. Both alignment of DNA sequences and the phylogenetic trees could exclude all the other species in Petrocosmea as the parental species except for Yanshan and P. martinii. Eight haplotypes in the 31 internal transcribed spacer sequences and six haplotypes in 42 cpDNA sequences were found from 14 individuals of Longianthera populations. The analyses of DNA sequences, haplotypes, and phylogenetic trees indicate that Longianthera is likely a hybrid species between its putative parents Yanshan and P. martinii, in which Yanshan might be the most possible maternal parent. Several factors may contribute to the natural hybridization between these two parental species in Petrocosmea, such as the overlapped geographic distribution, habitats, flowering periods, and shared pollinators. Finally, the new species of Yanshan and the natural hybrid species of Longianthera are described.

Key words: chloroplast DNA, Gesneriaceae, ITS, morphology, natural hybridization, Petrocosmea.