Hydrolithon cymodoceae (Foslie) comb. nov. (Corallinaceae, Rhodophyta) in southern Australia and its relationships to Fosliella

Abstract An examination of southernAustralian populations of Hydrolithon cymodoceae (Foslie) comb. nov. (Basionym: Melobesia cymodoceae Foslie) (Corallinaceae, Rhodophyta) has shown that plants vary considerably in thallus thickness. Tetrasporangial conceptacles have pore canals lined by a ring of conspicuous, elongate cells that arise from filaments interspersed amongst sporangial initials, do not protrude into the canal, and are oriented more or less perpendicularly to the thallus surface. These conceptacle features are considered diagnostic of Hydrolithon, and thus the species has been transferred into this genus. In addition, the species shows a number of distinctive features associated with reproduction. Tetrasporangial conceptacles usually contain a single zonately divided tetrasporangium lying horizontally within the chamber. Irregularly divided tetrasporangia, bisporangia, and undivided sporangia resembling monosporangia are also sometimes formed. Carposporangial conceptacles contain a single carp...