The new genus Crassothonna B. Nord. is described with 13 species transferred from the large and polymorphic genus Othonna L. Crassothonna species are perennial herbs, shrublets or shrubs with terete succulent leaves. The genus is mainly South African with a centre in Little Namaqualand and adjacent parts of the Western Cape, but is also represented by a few species in the eastern Cape Province, Natal and southern Namibia. Several species belong to the Gariep floristic element.