An account of Southern Australian Species of Mesophyllum (Corallinaceae, Rhodophyta)

Mesophyllum (Corallinaceae, Rhodophyta) is represented in southern Australia by at least four species. M. engelhartii and M. incisum have been reported from the region previously, M. macroblastum is newly recorded, and M. printzianum is newly described. Detailed accounts are provided for each species along with information on etymology, nomenclature and synonymy, collections examined, infraspecific taxonomy, and distribution, seasonality and habitat. Comparisons of southern Australian species with the type species of Mesophyllum, M. lichenoides, also are included. Of the nine additional entities that have been recorded from southern Australia under the generic name Mesophyllum, three (M. fumigatum, M. lemniscatum, M. versicolor) are considered heterotypic synonyms of M. engelhartii, three are referable to other genera of Corallinaceae (M. gabrielii to Lithothamnion; M. patena to Synarthrophyton; M. rupestre to Hydrolithon), two (M. lichenoides, M. neglectum) are based on misidentifications or questionable records, and one (M. squamuliforme) is treated as a species of uncertain status. Southern Australian specimens previously referred to Clathromorphum have been found to belong to Mesophyllum. As a prelude to the taxonomic accounts, a short historical introduction is provided along with a brief consideration of general morphological and anatomical features of Mesophyllum and a detailed analysis of characters that have been or could be used to delimit species within the genus. None of the at least 26 characters used by previous authors or the 34 quantitative characters examined during the present study were found to be of diagnostic value. By contrast, qualitative characters associated with tetrasporangial / bisporangial conceptacle roof morphology and anatomy have provided a reliable basis for delimiting the four southern Australian species from one another and from the type species of the genus, M. lichenoides. Concluding remarks, acknowledgments and references follow the taxonomic accounts.