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Two species of the coralline red algal genus Mesophyllum(Corallinaceae, Melobesioideae) are reported from the southernmost coral reefs in the western Indian Ocean at Sodwana Bay, Natal, South Africa. Specimens attributed to Mesophyllum erubescens(Foslie) Lemoine were compared with the type specimens of Lithothamnion erubescensFoslie and L. erubescensf. madagascariensisFoslie [= M. madagascariensis(Foslie) Adey]. The comparison showed that the local material and the type specimens are all conspecific, confirming previous suggestions that M. madagascariensisshould be subsumed in M. erubescens. Mesophyllum funafutiense(Foslie) Verheij was also recorded. These species are distinguishable on the basis of the structure of the roof and the pore of the tetrasporangial conceptacles, and on the size of tetrasporangial conceptacles and tetrasporangia.

Three species of Hydrolithonare reported from South Africa. Hydrolithon onkodesoccurs on the southernmost coral reefs in the western Indian Ocean at Sodwana Bay, Natal. Hydrolithon superficialesp. nov. is described on the basis of a distinctive layer of conceptacles that occur in a superficial layer of lightly calcified filaments with long, thin cells, that are sharply differentiated from the filaments of short cells in the thallus below. This species has been found only in the Sodwana Bay area of Natal Province. Lithophyllum samoënseFoslie is transferred to Hydrolithonon the basis of the anatomy of the tetrasporangial pore. It was also determined that H. samoënse(Foslie) comb. nov. is conspecific with Spongites wildprettiAfonso-Carrillo and Neogoniolithon illitus(Lemoine) Afonso-Carrillo. Hydrolithon samoënseis known to occur throughout South Africa.

The crustose coralline red alga, Sporolithon ptychoidesHeydrich, is recorded from tide pools, subtidal surge channels, and on rock substrate on the southernmost coral reefs in the western Indian Ocean, at Sodwana Bay National Park, Natal Province, South Africa. Sporolithon episporum(Howe) Dawson is reported from large tide pools, surge channels, and shallow subtidal rocks subjected to sand scour and inundation in the same area, as well as from the south-western Cape Province. The material of S. episporumis compared with the type specimen, and the latter is described and illustrated. The two species are distinguished on the basis of cell connections and the burying of sporangia. Sporolithon ptychoideshas both cell fusions and secondary pit connections, and sporangia buried in distinct rows. Sporolithon episporumhas secondary pits but not cell fusions, and generally sheds old sporangia.

Mesophyllum engelhartiiis a crustose coralline, melobesioid, red alga that is common in the Western Cape province and parts of the Eastern Cape province but becomes rare in KwaZulu-Natal. It occurs mainly on rocks and shells in the low intertidal and subtidal zones. The principal characters defining the species are the slightly to markedly prominent conceptacles and the structure of the tetra/bisporangial pore plate that is composed (in vertical section) of 4–6 somewhat elongate cells that are similar throughout and not specialized either in the conceptacle rim or in cells adjacent to pores.