Phylogenetic reconstruction of Didymocarpus and related genera in Gesneriaceae with establishment of two new genera

Abstract

The genus Didymocarpus Wall. is a core group of the subfamily Didymocarpoideae in Gesneriaceae with a complex taxonomic history. It has long been controversial to delimit Didymocarpus and its allies. We conducted phylogenetic reconstructions with high‐density sampling of Didymocarpus and related genera by using four nuclear ribosomal DNAs (external transcribed spacer [ETS], internal transcribed spacer [ITS], 18S, 26S) and five chloroplast DNAs (atpB‐rbcL, rpl16, rps16, trnH‐psbA, and trnL‐F). The results indicated that neither Didymocarpus nor Allocheilos are monophyletic. Based on molecular phylogenetic and morphological analyses, we delimitated the range of the Didymocarpus sensu stricto (s. str.) with two‐section division, and established a new genus Palmatiboea for species originally placed in Didymocarpus. This genus is remarkably distinguished from Didymocarpus s. str. not only in molecular phylogeny and morphology but also in its specific geographic distribution, in that it is found only in Southeast China. In addition, we proposed a new monotypic genus Hequnia for Allocheilos guangxiensis that is completely isolated in phylogeny, consistent with a range of remarkably distinctive morphological characteristics. Our results clarify the systematics of Didymocarpus and the delimitation between it and related genera with establishment of two new genera.