The marine Cyanophyceae of southern Africa are poorly known. Several marine substrata, along the Kwa-Zulu Natal Coast (South Africa) have been examined for cyanophytes. Enrichment cultures were prepared using Provasoli's enriched culture medium, and incubated under 20°C and 2Omumol.m-2 sect. Sixty-six taxa were identified. Eight failed to grow in either enrichment or unialgal cultures. Two of these were studied based only on the enrichment cultures and six only on the wild material. The sixty-six taxa belong to three orders, fourteen families and thirty-four genera. Fifteen genera ( Cyanosarcina, Chlorogloca, Chamaecalyx, Stanieria, Chroococcidiopsis, Solentia, Cyanosaccus, Hyella, cf. Pleurocapsa, cf. Borzia, Pseudanabaena, Limnothrix, Leptolyngbya, Kyrtuthrix, Trichormus) and thirty species [ Glocothece cf. rupestris, Aphanocapsa concharum, A. Iitoralis, Chamaecalyx (Dermocarpella algarvensis), Stanieria cf. cyanosphaera, S. sublitoralis, Xenococcus cf. pyriformis, Cyanosaccus piriformis, Hyella cf. immanis, Leptolyngbya cf. antarctica, L. cf. lurida, L. norvegica, Phormidium cf. boryanum, Geitlerinema cf. exile, G. Iemmermannii, Porphyrosiphon martensianus f rupestris, Symploca atlantica, S. funicularis, Hydrocoleum confluens, H. Iyngbyaccum, Microcoleus cf: tenerrimus, Oscillatoria cf. willed, Spirulina labyrinthiformis, S. meneghiniana, Kyrtuthrix maculans, Scytonema cf. arcangeli, Calotrix cf. pilosa, C. scopulorum, Nostoc cf. minutum and Trichormus cf. subtropicus ] are recorded for the first time in South Africa. The taxa isolated into unialgal cultures were studied under selected photon flux densities and temperature conditions and the morphology and size of the specimens were studied. Twenty-nine percent of the specimens displayed morphological variation, in addition to size variation and the remaining taxa exhibited size variation of different structures such as vegetative cells, heterocytes and akinetes. Most of the differences were statistically tested and they were significant at the 5% level. This study strongly shows that some characteristics used in the taxonomy of the Cyanophyceae are not stable and may vary depending on the environmental/cultural conditions under which the specimen grows.