| Abstract | The lack of homogeneity in all previously proposed, distinguishing characteristics 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 harvested members of the Gelidiales would assist resource management, agronomic practices, and marketing, even the distinction between two major groups, Gelidium and Pterocladia, has long remained controversial. In this study, the 18S ribosomal RNA (rRNA), internal transcribed spacer 1 (ITS1), 5.8S rRNA, and ITS2 regions of Gelidium latifolium (Greville) Bornet et Thuret, G. sesquipedale (Clemente) Thuret in Bornet et Thuret, G. vagum Okamura, Pterocladia lucida (Brown ex Turner) J. Agardh, and a recent segregate from Pterocladia, Pterocladiella capillacea (Gmelin) Santelices et Hommersand, were sequenced and analyzed. The ITS1, 5.8S rRNA, and ITS2 regions of G. arbuscula (Montagne) B=orgesen, G. canariensis (Grunow) Seoane-Camba, G. capense (Gmelin) Silva, and G. pristoides (Turner) Kützing were also sequenced. Phylogenetic analyses based on the 18S rRNA genes from four Gelidium species, Pterocladia lucida, and Pterocladiella capillacea, compared with 18S rRNA genes from several other red algae confirmed the division between Gelidium and the Pterocladia/Pterocladiella isolates and were consistent with the recently proposed segregation of Pterocladiella from Pterocladia. Analyses based on the ITS regions of seven Gelidium species, Pterocladia lucida, and Pterocladiella capillacea were completely consistent with the conclusions drawn from the 18S rRNA data. There were extensive length and sequence differences between Gelidium and Pterocladia/Pterocladiella. In addition, there were larger sequence differences between Pterocladiella and Pterocladia than exist among Gelidium isolates, in keeping with the recently proposed separation of the former two taxa. |
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