The validity of morphology-based species boundaries between the southern African representatives of the genus Tricolia Risso, 1826 was assessed using mitochondrial COI and 16S rRNA sequence data. Most phylogenies obtained from individual and combined genetic datasets recovered 10 of the southern African members of the genus as a monophyletic clade. No COI sequences of the 11th species (T. adusta) were available, but this species clustered among the other African species in the 16S rRNA phylogeny. Discrepancies between morphology and genetics were identified in two clades within which there was limited genetic variation and no differentiation between two groups of nominal species, comprising respectively T. africana (Bartsch, 1915) and T. capensis (Dunker, 1846), and T. bicarinata (Dunker, 1846), T. insignis (Turton, 1932) and T. kraussi (Smith, 1911). In both cases the distributions of the nominal taxa coincide with well-known biogeographic disjunctions, and there is evidence of overlapping and intergrading shell characters. We propose that both of these unresolved clades be recognized as single, phenotypically plastic species, for which the oldest available names are respectively T. capensis and T. bicarinata. Despite the resultant reduction in number of recognized species, the phasianellid fauna of southern Africa remains the most diverse in the world, with 10 endemic species and 3 tropical species extending south into KwaZulu-Natal.