Infrageneric classification of the genus Eleutherococcus Maxim.: (Araliaceae) with a new section Cissifolius

The genus Eleutherococcus Maxim. is divided into five sections based on the morphology; Eleutherococcus, Cissifolius C.H. Kim and B.-Y. Sun (sect. nov.), Acanthopanax (Decne. & Planch.) H. Ohashi, Cephalopanax (Baill.) H. Ohashi and Zanthoxylopanax (Harms) H. Ohashi. Section Acanthopanax is further divided into two subsections; Acanthopanax and lonostachyae (Nakai) C.H. Kim & R.-Y. Sun (comb. nov.). The new sect. Cissifolius is distinguished from others in having five fused carpels with free styles, solitary umbels at the end of branches, dioecious sexuality, and absence of tufted hairs in abaxial surface of leaf veins. The new section is most closely related to Acanthopanax in having free styles, solitary umbels, and dioecious sexuality. It is also related to Eleutherococcus in having five carpels and lacking tufted hairs on abaxial surface of leaves. Section Cephalopanax shares all characteristics other than the number of carpels with Eleutherococcus. Section Zanthoxylopanax is closely related to Acanthopanax in having two carpels with free styles, while it is also related to Cephalopanax by having bisexual flowers and umbels arranged in a simple cyme. Considering the evolutionary trend in the family Araliaceae, five-carpellate sections Eleutherococcus and Cissifolius are more primitive than two-carpellate sections Acanthopanax, Cephalopanax, and Zanthoxylopanax. Section Zanthoxylopanax seems to be intermediate between Acanthopanax and Cephalopanax.