NUCLEOTIDE-SEQUENCES OF SMALL-SUBUNIT AND INTERNAL TRANSCRIBED SPACERREGIONS OF NUCLEAR RIBOSOMAL-RNA GENES SUPPORT THE AUTONOMY OF SOME GENERA OF THE GELIDIALES (RHODOPHYTA)

The lack of homogeneity in all previously proposed, distinguishing cha racteristics has left the relationships of taxa within the Gelidiales as one of the most enduring taxonomic uncertainties in the Rhodophyta. Although a precise Knowledge of the taxonomy of commercially harveste d members of the Gelidiales would assist resource management, agronomi c practices, and marketing, even the distinction between two major gro ups, Gelidium and Pterocladia, has long remained controversial. In thi s study, the 18S ribosomal RNA (rRNA), internal transcribed spacer 1 ( ITS1), 5.8S rRNA, and ITS2 regions of Gelidium latifolium (Greville) B ornet et Thuret, G. sesquipedale (Clemente) Thuret in Bornet et Thuret , G. vagum Okamura, Pterocladia lucida (Brown ex Turner) J. Agardh, an d a recent segregate from Pterocladia, Pterocladiella cap illacea (Gme lin) Santelices et Hommersand, were sequenced and analyzed. The ITS1, 5.8S rRNA, and ITS2 regions of G. arbuscula (Montagne) Borgesen, G. ca nariensis (Grunow) Seoane-Camba, G. capense (Gmelin) Silva, and G. pri stoides (Turner) Kutzing were also sequenced. Phylogenetic analyses ba sed on the 18S rRNA genes from four Gelidium species, Pterocladia luci da, and Pterocladiella capillacea, compared with 18S rRNA genes from s everal other red algae confirmed the division between Gelidium and the Pterocladia/Pterocladiella isolates and were consistent with the rece ntly proposed segregation of Pterocladiella from Pterocladia. Analyses based on the ITS regions of seven Gelidium species, Pterocladia lucid a, and Pterocladiella capillacea were completely consistent with the c onclusions drawn from the 18S rRNA data. There were extensive length a nd sequence differences between Gelidium and Pterocladia/Pterocladiell a. In addition, there were larger sequence differences between Pterocl adiella and Pterocladia than exist among Gelidium isolates, in Keeping with the recently proposed separation of the former two taxa.