A large-scale phylogenetic analysis of dioscorea (Dioscoreaceae), with reference to character evolution and subgeneric recognition

Abstract

Dioscorea (Dioscoreaceae) is a diverse genus of more than 600 species. To understand relationships and character evolution within the genus, 273 samples from 183 species (including 28 newly sequenced species) based on four cpDNA regions were analyzed phylogenetically. The phylogenetic tree obtained comprised eleven well-supported major clades, most of which further consisted of more than two subclades. Comparisons with previously proposed infrageneric taxa (23 to 58 sections and associated ‘genera’) showed that some sections/‘genera’ are monophyletic and others polyphyletic. As in previous studies, ‘D. sect. Stenophora’ was sister to the rest of the genus. The present analyses of character state distribution on the tree confirmed that ‘D. sect. Stenophora’ is characterized by having rhizomes, monosulcate pollen and a diploid chromosome number based on x = 10 (plesiomorphies), whereas the rest of the genus has tubers and bisulcate pollen (apomorphies), but is diverse in regard to chromosome number, stem twining direction, fruit types and seed wing morphology. Based on molecular and morphological evidence, two subgenera, Dioscorea (= ‘D. sect. Stenophora’) and Helmia, are proposed. For subgenus Helmia, a revision of the infrageneric classification, especially for the species in the Old World, is needed.