A REVISION OF THE SYSTEMATICS OF THE NIZYMENIACEAE (GIGARTINALES, RHODOPHYTA) BASED ON POLYSACCHARIDES, ANATOMY, AND NUCLEOTIDE-SEQUENCES

Australian endemic family Nizymeniaceae, based on Nizymenia australis Sender, consists of three species in the two genera Nizymenia (1 sp.) and Stenocladia (2 spp.). We have reassessed the generic composition o f the family based on evidence from nonfibrillar wall polysaccharides, vegetative anatomy, and the nucleotide sequences of an internal trans cribed spacer, ITS 2, of the nuclear ribosomal cistron. Investigation of the polysaccharides by constituent sugar analysis, sulfate content determination, and methylation analysis, combined with gas chromatogra phy-mass spectrometry and infrared analysis, showed that the polysacch arides elaborated by the three species were branched, highly sulfated xylogalactans. These polysaccharides also contained significant amount s of mono-O-methyl galactose (5-8 mol% of total sugars), mainly 4-O-me thyl galactose. Although no discrete chemical structures could be assi gned to the polysaccharides, the analyses showed that those from Nizym enia australis and Stenocladia australis (Sender) Silva were more alik e than either was to that from S. furcata (Harvey) J. Agardh. This pol ysaccharide affinity was echoed by a suite of vegetative anatomical fe atures. However, the only likely synapomorphy was the presence of refr active, thick-walled medullary rhizines in both N. australis and S. au stralis. The ITS 2 sequences were inferred from direct sequencing of t he products of polymerase chain reaction amplification. Comparison of the ITS 2 sequences of its three species with those of two outgroups i ndicated that the family Nizymeniaceae is monophyletic but that inters pecific relationships within the family could not be resolved. We conc lude that there is insufficient evidence to separate any of the specie s from the rest at the genus bevel. Therefore, all three species are c onsolidated into the genus Nizymenia. This necessitates nomenclatural changes of Stenocladia australis to Nizymenia conferta (Harvey) Chiovi tti, Saunders, et Kraft comb.. nov.