First report of the melobesioid alga (Corallinales, Rhodophyta) Mesophyllum incisum (Foslie) Adey in South Africa

Mesophyllum incisum is reported and studied for the first time in South Africa. It has a thallus surface (SEM) with Leptophytum-type epithallial cells. Tetra/bisparangial conceptacles are mound-like and lack a peripheral rim but have a flattened pore plate. The rosette cells surrounding the tetrasporangial pores are distinct from surrounding roof cells (SEM, surface view) in being narrower, and sunken below the level of the surrounding pore plate. The cells of filaments bordering the tetrasporangial conceptacle pore canal differ from the other roof cells within the pore plate in being more elongate, narrower, and often more densely staining. Pore canal filaments also generally contain fewer cells than the surrounding filaments of the pore plate and the pore canal is more-or-less parallel sided. Our material agrees closely with the species as reported in Australia.