External morphological, palynological, chemotaxonomic, and molecular biological studies were conducted to evaluate the validity of the present classification system for the genus Dioscorea in Korea. In addition, the limits and variations of major taxonomic characters were identified, evolutionary trends were inferred, and interspecies relationships were estimated. External morphological characters, including the type of under-ground parts, direction of stem twining, presence or absence of bulbils, and direction of fruit growth, were confirmed to be useful characters for distinguishing infrageneric sections. Traits such as a papillate petiole, leaf shape, lobe splitting, presence or absence or hairs on the abaxial and adaxial surfaces of leaves, type of inflorescence, flowering form, color of the perianth, shape of fruit, position and shape of seeds, and shape of seed wings were found to be useful diagnostic characters distinguishing species.
Among the taxa of Dioscorea, the distinct characters of D. polystachya, D. japonica, D. nipponica, D. quinquelobata, D. coreana, and D. dokoro investigated to establish unambiguous diagnostic features that could be used to differentiate similar taxa.
Diagnostic characters such as the number of apertures and patterns on the surface of pollen grains were identified in palynological research, and are considered useful diagnostic characters for differentiating species. Hierarchical clustering analyses was conducted using the quantitative data of six useful features of Dioscorea to identify new diagnostic characters with respect to chemotaxonomy. In terms of sections, adenine and adenosine profiles were found to be consistent with the classification based on external morphology, and were thus deemed to be novel diagnostic characters supporting the morphological classification system.
Analysis of the cpDNA matK gene of Korean Dioscorea indicated that the classification system for taxonomic ranks above the section level was well reflected, and that Sect. Enanatiophyllum and Sect. Stenophora were clearly distinguished, which is consistent with the results obtained for cluster analysis based on 27 external morphological characters.
Taxonomic re-analysis revealed that Sect. Enanatiophyllum and Sect. Stenophora in the genus Dioscorea are clearly distinguished morphologically, and that Sect. Enanatiophyllum includes D. polystachya and D. japonica, whereas Sect. Stenophora includes D. nopponica, D. quinquelobata, D. tenuipes, and D. coreana. Moreover, we found the specific epithet of D. quinquloba to be erroneous. D. quinquloba has accordingly been renamed as D. quinquelobata, which has priority over the existing scientific name.
On the basis of the findings, we established a classification system for Korean taxa in the genus Dioscorea, for which we have prepared an associated species table and descriptions.