Molecular phylogenetic analyses of Euphorbiaceae tribe Epiprineae, with the description of a new genus, Tsaiodendron gen. nov., from south-western China

A phylogenetic analysis based on 18S nuclear ribosomal DNA and four plastid markers (atpB, matK, rbcL and trnLF) strongly supports the position of a new genus in Euphorbiaceae tribe Epiprineae (subfamily Acalyphoideae). Tsaiodendron dioicum gen. nov., sp. nov. is described and illustrated here as a new genus and species from Yunnan province, south-western China. The phylogenetic position of the new taxon is also supported by morphological and palynological evidence. Tsaiodendron is a distinct lineage sister to Cladogynos in tribe Epiprineae and is easily distinguished from related members of the tribe by the sexual system, inflorescence arrangement and presence of disc glands in the pistillate flower. Molecular divergence dating analysis based on matK, rbcL and trnL-F sequences suggests that Tsaiodendron originated in the late Miocene 10.42 Mya (95% HPD: 5.23-18.88 Mya). The origin of Tsaiodendron may be correlated with the Red River incision from south-western China. Tribe Epiprineae are shown to be monophyletic and phylogenetic relationships and evolutionary trends in the sexual system are also discussed based on our phylogenetic results.