Studies of tetrasporangial conceptacle development and anatomy have led to the conclusion that Spongites and Hydrolithon (of which Porolithon is considered to be a heterotypic synonym) are distinct genera of the Corallinaceae (Rhodophyta). In Australian populations of Hydrolithon reinboldii (Weber van Bossee et Foslie) Foslie, the type species of Hydrolithon, and Porolithon onkodes (Heydrich) Foslie, the type species of Porolithon, the tetrasporangial conceptacle pore canal is 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 roof surface. In Spongites fruticulosus Kutzing, the type species of Spongites, the pore canal is lined by cells that arise from peripheral roof filaments, protrude into the canal and are oriented more or less parallel to the roof surface. Tetrasporangial conceptacle development in Hydrolithon reinboldii and Porolithon onkodes is compared with that of Spongites fruticulosus, and Porolithon onkodes is transferred into Hydrolithon. Generic classification within the subfamily Mastophoroideae is discussed, and relevant historical and nomenclatural data are also included.
