Although differences in growth-form have been widely used in delimiting taxa of non-geniculate coralline red algae (Corallinales, Rhodophyta), there has been no consistent application of the more than 100 terms employed to describe the growth-forms present, and considerable confusion has resulted. This study of over 5000 populations of non-geniculate corallines from all parts of the world has shown that an intergrading network of growth-forms with 10 focal points is present: unconsolidated, encrusting, warty, lumpy, fruticose, discoid, layered, foliose, ribbon-like and arborescent. This focal point terminology can be used to describe any specimen or species of non-geniculate coralline in a consistent, easily interpretable manner. Details of the system are provided, the relationships of the system to past proposals are discussed, and the extent to which differences in growth-forms can be used as taxonomic characters in the non-geniculate Corallinales is reviewed.

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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.

Sporolithon (Sporolithaceae, Corallinales) is represented in southern Australia by S. durum (Foslie) Townsend et Woelkerling, comb. nov. The species and the development of male and female-carposporangial conceptacles and tetrasporangial compartments and sori are described in detail for the first time. Information on etymology, collections examined, distribution, seasonality and habit and comparisons with other species is also included. Published records of S. erythraeum from southern Australia have not been substantiated. Two further species have been reported under the generic name Archaeolithothamnion. Archaeolithothamnion australasicum is a species of uncertain status, while A. mirabile is conspecific with Lithothamnion muelleri Lenorrnand ex Rosanoff. Differences between the Sporolithaceae and the Corallinaceae, and the delimitation of genera within the Sporolithaceae, are reconsidered in relation to new data on S. durum. The Sporolithaceae is characterised by tetrasporangia that produce cruciately arranged spores and develop within calcified sporangial compartments, while the Corallinaceae is characterised by tetrasporangia that produce zonately arranged spores that do not develop in calcified sporangial compartments. Two genera of Sporolithaceae are recognised: Heydrichia, in which tetrasporangial compartments are enclosed by modified filaments to form sporangial complexes; and Sporolithon, in which tetrasporangial compartments are not enclosed by modified filaments and sporangial complexes are absent. The concepts of conceptacle and sorus also are reconsidered.

Lithothamnion (Corallinaceae, Rhodophyta) is represented in southern Australia by at least two species: L. muelleri, the type species of the genus, and L. indicum. Detailed accounts are provided along with a key to the species, and information on distribution, seasonality and habitat, nomenclature and synonymy, and infraspecific taxonomy. Two characters associated with tetrasporangial conceptacle roof anatomy are considered diagnostic of the two southern Australian species. Twenty-five characters used by other authors to separate species of Lithothamnion were examined; none were found to be diagnostic of L. muelleri or L. indicum, and only one (plant habit) was sometimes found to be useful as an ancillary character. None of the measured characters assessed could be used in a diagnostic or ancillary manner. The status and disposition of 22 other specific and infraspecific taxa ascribed to Lithothamnion and reported from southern Australia are summarised; 3 are considered synonyms of L. indicum or L. muelleri, 12 are referable to other genera, 6 are considered to be of uncertain status, and 1 constitutes an unconfirmed record.