Taxonomic studies of the genus Rhynchosia Lour. (Phaseoleae, Fabaceae) in South Africa: A review of section Chrysoscias

Abstract

BackgroundA taxonomic study of the genus Rhynchosia section Chrysoscias is presented. The section (as classified by Baker) comprises five taxa (four species and one variety). Previous revisions of the section by various botanists placed emphasis on leaflet shape and number of flowers as the primary characters to distinguish the species, however, these characters were found to be highly variable even within species. In addition, species distribution overlaps and therefore no conclusions can be made based on distribution patterns. ObjectivesThe aim of this paper is to provide diagnostic features of the four species of the section recognised in the current study, a key to the species, correct nomenclature, complete synonymy, typification, description, distribution maps as well as habitat notes. MethodologyWe studied herbarium specimens housed at BOL, JRAU, PRE, and those loaned from NBG (including SAM) supplemented by extensive field work. Morphological features were studied; measurements of characters recorded and illustrations were drawn using a camera lucida attachment. Anatomical and scanning electron microscopy studies were also carried out. ResultsThe current study revealed that there are four species in this section: Rhynchosia angustifolia, R. chrysoscias, R. leucoscias and R. microscias. The distribution and type of trichomes, degree of fusion in the uppermost calyx lobes and size of the standard petal are important taxonomic characters for distinguishing between the species. Leaflet shape can only be used in distinguishing R. angustifolia from the other species. The section is restricted to the Core Cape Subregion of the Greater Cape Region of South Africa. ConclusionFour species are recognised, Rhynchosia angustifolia, R. chrysoscias, R. leucoscias and R. microscias. R. leucoscias var. angustifolia is here synonymised with R. angustifolia and the latter name is preserved to take Jacquin's earlier name of Glycine angustifolia referring to the narrow leaflets. The distributions and types of trichomes are reported here for the first time.