In continuing studies on the taxonomy of non-geniculate, coralline algae from South Africa, stipes of the kelp, Ecklonia maxima, in the subtidal zone of Western Cape Province, were frequently observed to be covered with rosy-pink encrusting coralline algae. The reproductive morphology and anatomy of these plants show that they belong to the subfamily Melobesioideae and the genus Synarthrophyton. The specimens agree closely with the holotype of Lithothamnion capense f. eckloniae described by Foslie on the basis of South African material. Synarthrophyton eckloniae is described in detail; the species appears to be endemic to Western Cape Province. Another crustose coralline alga from the subtidal zone of South Africa was found to be conspecific with a syntype of Lithothamnion magellanicum and the lectotype and isolectotype of Lithothamnion muelleri f. neglecta. These are now shown to conform to the generic concept of Synarthrophyton on the basis of their concordance with the characters of that genus. South African material of S. magellanicum is compared with the type specimen of Lithophyllum schmitzii with which it had been synonymized and it is concluded that the two species are distinct. It can be distinguished from type specimens of Lithothamnion lamellatum and L. chatamense, with which previous authors had suggested it might be conspecific, on the basis of anatomical characters, despite similarity in habit. The last two species have not been recorded in South Africa.