THE MELOBESIOID ALGA MESOPHYLLUM-ENGELHARTII (RHODOPHYTA, CORALLINACEAE) IN SOUTH-AFRICA

Mesophyllum engelhartii is 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. The following type specimens, described by Foslie on the basis of South African material, are shown to be conspecific with M. engelhartii: the lectotype and isolectotype of Lithothamnion discrepans, and the holotype of Lithothamnion synanablastum f. speciosa. The isotype of Goniolithon elatocarpum is probably also conspecific but bears only non-diagnostic carposporangial conceptacles. As the epithet engelhartii has nomenclatural priority, the other taxa are now subsumed in Mesolphyllum engelhartii which is a common southern Australian species.