Phylogenetic analyses of 18S rDNA gene data for Choreonema thuretii (Corallinales, Rhodophyta) and available data for other coralline red algae indicated that Choreonema belongs to the same lineage as other taxa of Corallinales possessing tetra/bisporangial conceptacles with multiporate plates. These results, when integrated with extant morphological/anatomical data, ultrastructural data, and taxonomic data led to the conclusion that all taxa of Corallinales possessing multiporate conceptacles belong to a distinct family, the Hapalidiaceae. Recognition of the Hapalidiaceae as a distinct family was supported both phylogenetically and phenetically. The Hapalidiaceae includes those taxa of Corallinales whose tetrasporangia produce zonately arranged spores and whose tetra/bisporangia are borne in conceptacles, produce apical plugs, and develop beneath multiporate plates. The Hapalidiaceae includes the subfamilies Choreonematoideae, Melobesioideae, and Austrolithoideae, formerly placed in the Corallinaceae sensu lato. The Choreonematoideae lack cell connections between adjacent vegetative filaments and have a multiporate plate that is acellular at maturity, consisting only of a calcium carbonate matrix. The Austrolithoideae and Melobesioideae both have cellular pore plates; taxa of Melobesioideae have cell fusions between cells of adjacent vegetative filaments, whereas taxa of Austrolithoideae lack cellular connections between adjacent vegetative filaments. Inclusion of the Austrolithoideae in the Hapalidiaceae was based entirely on morphological/anatomical evidence; molecular evidence currently is lacking. Relevant historical and nomenclatural data are included.

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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.

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.

Research purpose and findingsCoralline algae are key biological substrates of many carbonate systems globally. Their capacity to build enduring crusts that underpin the formation of tropical reefs, rhodolith beds and other benthic substrate is dependent on the formation of a calcified thallus. However, this important process of skeletal carbonate formation is not well understood. We undertook a study of cellular carbonate features to develop a model for calcification. We describe two types of cell wall calcification; 1) calcified primary cell wall (PCW) in the thin-walled elongate cells such as central medullary cells in articulated corallines and hypothallial cells in crustose coralline algae (CCA), 2) calcified secondary cell wall (SCW) with radial Mg-calcite crystals in thicker-walled rounded cortical cells of articulated corallines and perithallial cells of CCA. The distinctive banding found in many rhodoliths is the regular transition from PCW-only cells to SCW cells. Within the cell walls there can be bands of elevated Mg with Mg content of a few mol% higher than radial Mg-calcite (M-type), ranging up to dolomite composition (D-type).Model for calcificationWe propose the following three-step model for calcification. 1) A thin (< 0.5 μm) PCW forms and is filled with a mineralising fluid of organic compounds and seawater. Nanometer-scale Mg-calcite grains precipitate on the organic structures within the PCW. 2) Crystalline cellulose microfibrils (CMF) are extruded perpendicularly from the cellulose synthase complexes (CSC) in the plasmalemma to form the SCW. 3) The CMF soaks in the mineralising fluid as it extrudes and becomes calcified, retaining the perpendicular form, thus building the radial calcite. In Clathromorphum, SCW formation lags PCW creating a zone of weakness resulting in a split in the sub-surface crust. All calcification seems likely to be a bioinduced rather than controlled process. These findings are a substantial step forward in understanding how corallines calcify.

This paper provides the first monographic account of south-eastern Australian representatives of the Hapalidiaceae (Corallinales, Rhodophyta). The Hapalidiaceae includes those Corallinales whose tetrasporangia produce zonately arranged spores, and whose tetrasporangia/bisporangia are borne in conceptacles, produce apical plugs, develop beneath multiporate plates or roofs, and are not enclosed individually within calcified sporangial compartments. The Hapalidiaceae contains the subfamilies Choreonematoideae, Melobesioideae and Austrolithoideae, all formerly placed in the Corallinaceae sensu lato. The Choreonematoideae is represented in south-eastern Australia by a single species, Choreonema thuretii. The Melobesioideae is represented by five genera (Melobesia, Lithothamnion, Phymatolithon, Mesophyllum, Synarthrophyton) and eight species. Synarthrophyton pseudosorus sp. nov. is newly described. The presence of tetrasporangial conceptacles occurring in irregularly shaped dense clusters that contain both discrete conceptacles and fused groups of conceptacles delimits this species from all other species of Synarthrophyton. Morphological and anatomical accounts are provided, including keys, information on distribution, habitat and nomenclature. Brief biogeographic comparisons between south-eastern Australia and neighbouring regions are also made.

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