Molecular and morphological evidence for a new species of Pogostemon (Lamiaceae) from Hainan Island, China

Pogostemon hainanensis, a new species of Lamiaceae from Hainan Island, China, is described. The phylogenetic position of the new species within Pogostemon was investigated based on analyses of the nuclear ribosomal internal transcribed spacer (nrITS) and five plastid markers (viz. matK, psbA-trnH, rbcL, rsp16, trnL-F). The results show that P. hainanensis is supported to be a member of subgenus Pogostemon and is sister to P. parviflorus, a species widely distributed from Eastern Himalaya, through the Indo-China peninsula to China. Morphologically, the new species can be distinguished from all the other taxa of subgenus Pogostemon in having long petioles usually 4.5-11.5 cm in length, and the calyx teeth 2/3 to subequal as long as the calyx tube. The new species differs from P. parviflorus further by its obviously double serrate leaf margin, spikes of inflorescence usually 2.5-8.0 cm long, calyx 4-5 mm long and corolla 6-7 mm long.