Phylogenetic Relationships, Character Evolution, and Two New Species in Hemiboea (Didymocarpoideae, Trichosporeae)

Two new species, Hemiboea xishuiensis X.X. Bai and Hemiboea cehengensis X.X. Bai, from Guizhou, China, are described here. We performed a molecular phylogenetic analysis of the two new species and 28 taxa within Hemiboea based on ITS and trnL-F, which shows that the phylogenetic tree of Hemiboea forms three major clades: H. fangii Chun ex Z.Yu Li occupies one clade exclusively (Clade I), H. xishuiensis, H. cehengensis, H. parvibracteata W.T. Wang & Z.Yu Li, H. ovalifolia (W.T. Wang) A. Weber & Mich. Möller, and H. kaiyangensis T. Peng & S.Z. He constitute a highly supported clade (Clade II), and the remaining taxa are clustered into the third clade (Clade III). Furthermore, this study traced the evolution of eight important morphological characters in Hemiboea and determined their ancestral states. The results show that the involucre is not early deciduous, the calyx is 5-sect from the base, the corolla is hairy outside, there are two protuberances and trichomes on the inner abaxial surface of the corolla, and there is a hairy ring above the base on the inner face of the corolla, the ovary is glabrous, and these characters may be the ancestral states of Hemiboea; H. fangii is the most primitive species of Hemiboea found to date; whether the involucre is early deciduous and whether there are two protuberances on the inner ventral surface of the corolla may be the key characters for the classification of sections under Hemiboea. This study not only enriches the species diversity of Hemiboea in China but also provides a new inspiration for the infrageneric classification of Hemiboea.