The objective of the study was to determine whether the species could be arranged in a competitive hierarchy and to establish whether the interactions were symmetrical or asymmetrical. Indices of competitive ability indicated a hierarchy, namely Senecio arenarius > Dimorphotheca sinuata > Ursinia cakilefolia. The stronger competitors (S. arenarius and D. sinuata) were characterized by intraspecific competition having a stronger effect than interspecific competition from U. cakilefolia. The weakest competitor (U. cakilefolia) was characterized by interspecific competition from D. sinuata and S. arenarius having a greater effect than intraspecific competition. Total above-ground dry mass per plant of the stronger competitors was enhanced in a mixture, especially when grown with U. cakilefolia. However, U. cakilefolia performed just as well or better in a monoculture than in a mixture. Results indicated that some degree of niche differentiation exists, which may allow coexistence between the stronger competitors (S. arenarius and D. sinuata) and the weakest competitor (U. cakilefolia). Long-term coexistence between S. arenarius and D. sinuata, with similar competitive abilities, may be brought about by temporal or spatial refuges. The constantly changing conditions in Namaqualand promote coexistence, as no species is able to retain a competitive advantage long enough to exclude the others. In general, biomass allocation patterns showed no specific trend in response to competitive stress.