Diversity and pasture potential of legumes indigenous to southern Africa

Abstract

This study records all known legume (Leguminosae/Fabaceae) species indigenous to South Africa, Lesotho and Swaziland to establish distribution patterns and optimum climatic and soil conditions for growth. The main purpose was to propose a list of legume species for further evaluation of their pasture potential. Collection data supplied by the National Herbarium (PRE) Computerised Information System were recorded to establish the distribution patterns of species based on the bioregions vegetation map. A total of 1 654 species are known to be indigenous, representing 24 tribes and 122 genera. The grouping of legume species into five main clusters and 16 Leguminochoria is ecologically described, with the highest legume species richness found in the Northern Mistbelt Forest. Key and diagnostic species are provided for each Leguminochorion. Soil pH and mean annual minimum temperature were found to be the main drivers for distinguishing between legume assemblages. The optimum climatic and soil conditions for growth are described as well as the available descriptive attributes for species recorded. Information on the range of tolerance of most species to abiotic factors is presented. Mean annual rainfall and soil pH are highly correlated with the distribution pattern of most species, followed by mean annual minimum temperature. Legume species adapted to a wide range of soil pH levels and low soil phosphorus levels are recorded. Existing data on the cultivation and grazing or browsing status of indigenous legumes were used to select 584 species found mainly in the Central Bushveld, Mopane and Lowveld Bioregions to be further evaluated for their pasture potential. Known characteristics were used to categorise species. Species contained in the tribe Phaseoleae are of special interest since it contains most of the genera with present-day agricultural value, i.e. Eriosema, Rhynchosia and Vigna species are listed as having high potential as pasture species. This study has shown that the descriptive and distribution data accumulated by botanists (notably taxonomists) could be of beneficial use in meeting agricultural objectives. Indigenous legumes are adapted to a wide range of soil and climatic conditions and represent a valuable but largely unexploited natural resource for pasture development and soil conservation practices.