Background and aims – The grasslands of southern Africa are threatened by habitat transformation and invasive alien species. However, the resultant plant species loss per unit area cannot be quantified, as the true richness of grassland have not been determined accurately and current estimates of richness are generally based on once-off site visits. The aim of this study was to quantify and compare the species richness of selected transformed and untransformed grasslands of tropical and temperate regions in South Africa. The study sites were located in four grassland vegetation units: KwaZulu-Natal Coastal Belt and Maputaland Woody Grassland (tropical), and Paulpietersburg Moist Grassland and Rand Highveld Grassland (temperate). Methods – Thirty-two plots of 10 × 10 m were sampled at the four sites, namely eight in each of the vegetation units. At each site four plots were sampled in untransformed grassland and four in adjacent transformed grassland. Thorough floristic sampling of each plot was undertaken three times during the peak growing seasons. Key results – Plant species richness was higher for untransformed grassland than transformed grassland, and is higher than what was previously estimated. Species richness is not severely affected by alien cover and richness, as species losses are made up by better adapted native and alien species entering the transformed habitat. Rare species and habitat specialists are displaced. The type of transformation has a pronounced effect on species richness. Conclusion – Plant species richness of grassland is higher than previous estimates. Increasing alien cover and richness reduces the species richness of certain grassland growth forms and replaces species of conservation importance such as endemics.