Heydrichia cerasina sp nov (Sporolithales, Corallinophycidae, Rhodophyta) from the southernmost tip of Africa

A new species of Heydrichia (Sporolithales), Heydrichia cerasina sp. nov., is described, found only on pebbles in the low intertidal zone along a 10 km stretch of the South African south coast from Cape Agulhas to Struisbaai. The species is characterized by the following suite of features that distinguish it from the other two species of Heydrichia found in South Africa: (1) unusual cherry-red colour when freshly collected; (2) uniformly warty growth form; (3) relatively thin crust (up to 1400 mu m thick); (4) tetra/bisporangial son comprised of mostly single sporangial chambers; and (5) unbranched spermatangial structures distributed on the floor, walls, and roof of the mature male conceptacle. The species appears to be most closely related to Heydrichia homalopasta from Australia. This study has affirmed that the distribution of spermatangial structures within male chambers is a feature that cannot be used to separate Heydrichia from Sporolithon, the only other genus in Sporolithales, although features of thallus construction and tetra/bisporangia continue to distinguish the genera. A key to the southern African species from the order Sporolithales is provided.