Abstract
M.Sc. (Botany)
The genus Rhynchosia Lour. (commonly known as snout bean) is the largest in the subtribe Cajaninae, comprising about 230 species distributed throughout the tropics and subtropics with about 73 species native to southern Africa and one species (R. phaseoloides (Sw.) Kuntze) that is cultivated in the region. In southern Africa the genus is widely distributed throughout the entire region with abundance more on the north easterly parts. A taxonomic revision of four of the five sections of the genus Rhynchosia Lour. (Fabaceae, Phaseoleae) in South Africa (Arcyphyllum (Ell.) Torrey and Gray, Chrysoscias E.Mey., Cyanospermum (Wight and Arnott) Benth., Polytropia (Presl) Harv.) is presented. Details of the recognised species are illustrated, diagnostic characters of the sections and for the first time aspects of the anatomy of the genus in South Africa are reported. Results obtained from morphology and anatomical study support the current sectional classification and recognises 2 spp. in sect. Archyphyllum, 5 spp. in sect. Chrysoscias, 1 sp. in sect. Cyanospermum and 3 species in sect. Polytropia. Anatomical studies of the leaf blade and petiole revealed that there are three types of glandular trichomes that occur in the genus: spherical capitate, ellipsoid capitate, bulky capitate. These glandular trichomes have unicellular or multicellular bases and are often found in depressions on the epidermis, sometimes connected to vascular units by a parenchymal sheath on the epidermis of the petiole and abaxial surface of the leaf. Non-glandular trichomes are also present consisting of normal and bulbous-based hairs consistently throughout the four sections and consist of uni- to multicellular cells with one to three cells. Sectional and species nomenclature, complete typification, descriptions and geographic distribution for each taxon are presented. A key to the species in each section, based mainly on the leaf characters and the type and distribution of trichomes is presented. The anatomical structure of the trichomes has given an insight into taxonomic relationships between species, especially in the section Chrysoscias.