Patterns of genetic and morphological variation among eight populations of Patella barbara along the coast of South Africa were examined to see whether reported differences in shell morphology and behaviour between the west and east coasts were mirrored by other morphological and/or genetic differences. Morphological analyses of radular structure, gut-loop coiling and sperm microstructure revealed no differences between the populations. Discriminant functions analysis based on shell morphometrics showed major overlap between populations and failed to separate them. Electrophoretic analysis of 17 enzyme loci gave an overall genetic identity (Nei) value of 0.995, a value which lies within the generally accepted range for conspecific populations. In two of the populations, at Dwesa and Arniston, individuals were found to be ‘gardening’ algal resources. At Clovelly, a ‘normal’ form of P. barbara was found on the rocks, whereas a reduced and tall-shelled form occurred on the ascidian Pyura stolonifera, demonstrating phenotypic morphological plasticity. It was concluded that different populations of Patella barbara are both morphologically indistinguishable and genetically homogenous along the coast of South Africa, thus providing good evidence for widespread gene flow.