Flower morphology and phylogenetic analysis of some Dioscorea species of the section Stenophora (Dioscoreaceae)

The section Stenophora is the most basal clade in the phylogeny of the genus Dioscorea. Most of the species in the section have not been morphologically and embryologically investigated and phylogenetic relationships among species of this section are not very clear. Embryological features, such as the structure of anthers, pollen, ovules, embryo sacs etc., less undergo phenotypic variability and can be used as important characters for systematics and phylogeny. Comparative morphological and embryological analyses of the reproductive structures in 5 Dioscorea species of the section Stenophora (D. balcanica, D. caucasica, D. deltoidea, D. nipponica, D. villosa) are presented. Four characters, which may be significant for systematics of this section as well as the whole genus Dioscorea, were designated: (1) heteromorphism of the stamens in the male flower; (2) the structure of the stigma; (3) the structure of the ovule; (4) the type of female gametophyte development. It was shown that D. balcanica, D. caucasica, D. deltoidea are characterized by similar morphological features and differ from D. nipponica and D. villosa. Analysis of haplotype networks showed that the section Stenophora consists of genetically close species, that was confirmed by the phylogenetic tree of this section. The morphological similarity of D. balcanica, D. caucasica and D. deltoidea is consistent with their location on the phylogenetic tree. However, detailed morphological, embryological and molecular phylogenetic studies of a larger number of species are needed for more accurate interpretation of the Stenophora phylogenetic system.