Biogeography of Psilosiphon (Batrachospermales, Rhodophyta) in Australia and New Zealand

The freshwater red algal genus Psilosiphon. (Batrachospermales) is :known f rom the northern tip of North Island (New Zealand), the central coast of Ne w South Wales (Australia) and southwest Tasmania (Australia). There is litt le morphological variation among or within collections from these disjunct regions and sexual reproduction has not been convincingly demonstrated. All known locations - five collections (four along one stream reach) from sout hwest Tasmania, and one collection each from New South Wales and North Isla nd - were sampled for molecular study. Trees based on the rbcL chloroplast gene and the limited ITS1-5.8S rDNA-ITS2 nuclear region show the Tasmanian collections grouped together, with the rbcL data supporting the New Zealand collection as a sister taxon, and the New South Wales collection basal to this clade (the unrooted ITS data are uninformative outside the Tasmanian c lade). Because this phylogeny is strongly supported by the rbcL data, and t he rbcL base-pair differences between collections from the three regions ar e large (4.4-7.7 %), it is proposed that three genetic races be recognised within Psilosiphon scoparium. Due to the absence of corroborating morpholog ical data and sufficient independent molecular data for complete congruence , these races are not given formal taxonomic recognition. However the phylo geny supports an origin for these genetic races prior to the separation of New Zealand from Gondwana. (C) 2000 Adac/Editions scientifiques et medicale s Elsevier SAS.