The Sporolithaceae (Corallinales, Rhodophyta) in south-eastern Australia: taxonomy and 18S rRNA phylogeny

Abstract

The family Sporolithaceae (Corallinales, Rhodophyta) is represented in south-eastern Australia by two species: Heydrichia homalopasta and Sporolithon durum. Morphological and anatomical accounts are provided, including a key to species, and information on distribution, seasonality, habitat and nomenclature. Analyses of characters previously proposed for the delimitation of genera within the Sporolithaceae show similarities, overlaps or uncertainties for most character states. The presence of an involucre surrounding the tetrasporangial compartments in Heydrichia (and the absence of an involucre in Sporolithon) has proven a useful and stable character in delimiting these genera. Data from south-eastern Australian collections of H. homalopasta have also shown that features relating to tetrasporangial compartments are useful in delimiting H. homalopasta from other species of Heydrichia. These include the presence of solitary tetrasporangial compartments and the absence of successive tetrasporangia. New 18S rRNA sequence data from S. durum and H. homalopasta were combined with selected published sequences of coralline red algae. All phylogenetic reconstruction methods resolved H. homalopasta and H. woelkerlingii as sibling taxa in a strongly supported clade. Molecular data are consistent with the known morphological data and with recognition of H. homalopasta as a distinct species. Phylogenetic reconstructions consistently placed Sporolithon and species of Heydrichia in a strongly supported clade with Rhodogorgon carriebowensis, a species generally regarded as belonging to a separate order (Rhodogorgonales). This result is inconsistent with known morphological and reproductive features.