A taxonomic reassessment of Hydrolithon Foslie, Porolithon Foslie and Pseudolithophyllum Lemoine emend. Adey (Corallinaceae, Rhodophyta) and their relationships to Spongites Kützing

Critical studies of relevant generitype specimens and of numerous southern Australian populations have led to the conclusions that diff erences in trichocyte occurrence and arrangement, basal region organization and cell size cannot be used to delimit genera within the Spongites complex (Corallinaceae, Rhodophyta). Hydrolithon Foslie and Porolithon Foslie therefore are treated as heterotypic synonyms of Spongites and Pseudolithophyllum sensu Adey is also considered congeneric with Spongites. Solitary trichocytes, vertical rows of trichocytes and horizontal rows or fields of trichocytes all can occur within single plants. Plants otherwise identical may or may not produce trichocytes. Both unistratose and multistratose basal regions can develop in primary portions of the same plant and abrupt transitions from one to the other can occur. Cell sizes of generitype specimens overlap and a broad continuum of cell sizes occur in southern Australian plartts. The circumscription of Spongites has been altered to take account of these results and the relationships of Spongites to other genera of nongeniculate Corallinaceae are then considered. Relevant historical and nomenclatural data are included.