Woody plant richness across southern Africa was analysed and related to climate–based water–energy dynamics. The analyses, which were based on an equal–area grid system, were undertaken at the genus and family levels and compared with results previously obtained at the species level. In all cases– climate accounts for most of the variation in richness (74–79%,). with richness being a linear function of liquid water and a parabolic function of energy. There is some variation in the particulars of climate's relationship to richness between the three taxonomic levels considered. But, the overall similarity of the outcomes at all three taxonomic levels supports the view that independent and predictable geographic variation in water-energy dynamics exerts a first-order control on the realised distributional ranges, and thus richness, of surviving and evolving taxa.