THE PHYLOGENETIC AFFINITIES OF NOTHEIA-ANOMALA (FUCALES, PHAEOPHYCEAE) AS DETERMINED FROM PARTIAL SMALL-SUBUNIT RIBOSOMAL-RNA GENE-SEQUENCES

Partial nucleotide sequences of the nuclear small-subunit ribosomal RNA genes (SSU); as inferred from polymerase chain reaction (PCR)-amplified products, have been determined for Caulocystis cephalornithos (Labillardiere) Areschoug (Cystoseiraceae), Hormosira banksii (Turner) Decaisne (Hormosiraceae), Sargassum vestitum (R. Brown ex Turner) C. Agardh (Sargassaceae) and Notheia anomala Harvey et Bailey (Notheiaceae). These taxa art referred to three of the six families currently placed in the order Fucales, plus the monotypic Notheiaceae, which has variously been placed in the Chordariales, the Fucales or the Notheiales. Our investigations indicate that the SSU gene provides suitable divergence for assessing relationships among the fucalean families. Phylogenetic analyses of the partial SSU gene sequences ally the Notheiaceae with the Fucales, although not closely with its virtually obligate host, Hormosira banksii of the monotypic Hormosiraceae. The data are equivocal as to the positioning of the Notheiaceae relative to the fucalean families, and a review of anatomical and reproductive features is provided. We concur with earlier suggestions made on the bases of life history and anatomy that the Notheiaceae is the sister group to the Fucales sensu stricto. Although the issue may never be fully resolved, we suggest that the evidence points strongly to Notheiaceae being included in the Fucales rather than constituting a separate order.