Abstract
Abstract : The genus Rhynchosia Lour. was first introduced by Loureiro, to accommodate the species Rhynchosia volubilis Lour. It derives its name from the Greek word “rhynchos” which means a beak, snout or horn, in reference to the shape of the keel petals. Rhynchosia is a relatively large genus with more than 230 species occurring throughout the tropics and subtropics, with about 77 species indigenous to southern Africa. Within the subtribe Cajaninae, Rhynchosia is closely related to the genus Eriosema (DC) Desv. However, it can be distinguished from the latter by the structure of the funicular attachment of the seed in relation to the hilum. In Rhynchosia the funicular attachment is in the centre of the hilum, while in Eriosema the attachment is at the end of the hilum. It also has affinities with the genus Bolusafra Kuntze, however, previous preliminary molecular studies have shown that Bolusafra is congeneric with Rhynchosia. This project is part of ongoing taxonomic studies in the type section Rhynchosia, and its main aim was to revise the R. minima complex and provide a synopsis of the ethnomedicinally important species. The secondary aim of the study was to screen these plants for their antimicrobial activities based on their traditional use. However, due to unavailability of some of the plants in the field, despite numerous attempts, not all species could be screened. The third aim was to conduct qualitative evaluation of the phytochemical properties of these plants. The morphological studies were conducted by examining herbarium specimens and during field surveys, while type specimens were studied online. Taxonomic studies revealed that there are five infraspecific taxa in the R. minima complex in southern Africa, these include two newly described varieties (R. minima (L.) DC. var. glandularis M.S. Mothogoane and Moteetee and R. minima (L.) DC. var. magniflora M.S. vi Mothogoane and Moteetee). A taxonomic key to the infraspecific taxa of R. minima complex is provided, in addition, the correct nomenclature, typification, and distribution maps for all taxa studied are presented. Various literature sources and databases were consulted for the compilation of ethnomedicinal Rhynchosia species. The survey showed that in addition to R. minima, there are eight other ethomedicinally important species of Rhynchosia species in southern Africa, namely; R. adenodes Eckl. & Zeyh., R. albissima Gand., R. caribaea (Jacq.) DC., R. densiflora (Roth) DC., R. harveyi Eckl. & Zeyh., R. hirta (Schumach.) Meikle, R. resinosa (Hochst.ex A.Rich.) Meikle, and R. sublobata. These species are used for the treatment of various human infections, including gastrointestinal disorders, respiratory tract infections (RTIs), skin conditions, and sexually transmitted infections (STIs). However, only three of these species (R. adenodes, R. caribaea and R. harveyi) are used medicinally in southern Africa, while the others are used elsewhere across their wider geographical distribution ranges. Based on the microbial inhibitory concentrations (MIC) results, Rhynchosia hirta and R. sublobata showed noteworthy antibacterial activities against Escherichia coli and Staphylococcus aureus, which are the major causative pathogens for gastrointestinal problems such as diarrhoea (This explains the efficacy of these species in the treatment of stomach problems). The studied species (R.adenodes, R.albissima, R. caribaea, R.hirta, R.minima and R.sublobata) were found to contain a number of chemical constituents including, alkaloids, coumarins, flavonoids, phenols, saponins, tannins, and terpenoids, which might explain the ethnobotanical uses of these species in traditional medicine.
M.Sc. (Botany)