Based on specimen records, published sources and own observations, an updated list of plant species is presented for the Sperrgebiet, the southwestern corner of Namibia. This area is in the transitional zone of winter and summer rainfall in Namibia and a remarkable 1038 species of flowering plants, 13 ferns and 22 mosses and their relatives occur. This comprises nearly 25% of the entire flora of vascular plants in Namibia and some 21% of the plant diversity of the Succulent Karoo Biome. We conclude that the Sperrgebiet is undoubtedly one of Namibia's prime plant diversity hotspots.