The Dunbar Valley serpentinite outcrop has a flora comprising 254 taxa (species and below) in 172 genera and 63 families. Dunbar Valley has more species than other studied serpentinite sites in the Barberton Greenstone Belt (BGB). The genus Senecio is the most speciose genus in the BGB. The level of species endemism at Dunbar Valley is 2.0%. Most of the serpentinite endemics in the BGB show phytogeographical affinities with the Sudano‐Zambezian Region. Six modified‐Whittaker plots, three on serpentinite and three on non‐serpentinite soils, were sampled. Sørenson's index was 0.312, indicating low similarity in species between serpentinite and non‐serpentinite sites (β‐diversity) at Dunbar Valley, as at other sites in the BGB. α‐diversity (using the Shannon–Wiener index) for the serpentinite was 2.631 ± 0.901 and for the non‐serpentinite, 2.886 ± 0.130. However, a Student's t‐test showed no significant difference in α‐diversity between the two habitats. There was also no significant difference in species richness between serpentinite and non‐serpentinite sites. Total species showed negative correlations with total nickel, altitude and serpentinite outcrop size (area) for six sites in the BGB. Number of endemic taxa showed no correlation with environmental variables. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143, 271–285.