NUCLEAR SMALL-SUBUNIT RIBOSOMAL-RNA GENE-SEQUENCES FROM REPRESENTATIVE CERAMIACEAE (CERAMIALES, RHODOPHYTA)

Recently published phylogenetic trees derived from nuclear small-subun it (SSU) ribosomal RNA gene sequences indicate particularly curious re lationships for two species of the Ceramiaceae: Ceramium nodulosum and Griffithsia globulifera. To test these earlier results we have determ ined the SSU sequences for Anotrichium furcellatum, Ceramium macilentu m, Crouania attenuata and Griffithsia monilis, all members of the Cera miaceae, as well as for Gelidium pusillum of the Gelidiales. These are included in a multiple alignment containing representatives of all th e 'higher' florideophyte orders. Our results indicate that an SSU sequ ence previously published for Griffithsia globulifera differs by only five nucleotide changes from a published gene for Gelidium vagum, as w ell as from the gene of Gelidium pusillum sequenced by ourselves. The two species of Gelidium differ from one another at four sites. In shar p contrast, our data for Griffithsia monilis strongly ally this specie s with other representative Ceramiales. The only other published ceram iacean SSU sequence, that of Ceramium nodulosum, allies only weakly, i f at all, with the representative gene sequences available for members of the Dasyaceae, Delesseriaceae and Rhodomelaceae (Ceramiales) in ph ylogenetic analyses. Addition of the Ceramium macilentum gene to the m ultiple alignment strongly indicates monophyly for the Ceramiales (exc luding G, globulifera) in ail the phylogenies generated from the molec ular data. We conclude that the lack of strength for a monophyletic Ce ramiales in previous reports is largely attributable to the effects of the Ceramium nodulosum sequence on phylogenetic analyses.