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 RN A genes (SSU); as inferred from polymerase chain reaction (PCR)-amplif ied products, have been determined for Caulocystis cephalornithos (Lab illardiere) Areschoug (Cystoseiraceae), Hormosira banksii (Turner) Dec aisne (Hormosiraceae), Sargassum vestitum (R. Brown ex Turner) C. Agar dh (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 variou sly been placed in the Chordariales, the Fucales or the Notheiales. Ou r investigations indicate that the SSU gene provides suitable divergen ce for assessing relationships among the fucalean families. Phylogenet ic analyses of the partial SSU gene sequences ally the Notheiaceae wit h the Fucales, although not closely with its virtually obligate host, Hormosira banksii of the monotypic Hormosiraceae. The data are equivoc al as to the positioning of the Notheiaceae relative to the fucalean f amilies, and a review of anatomical and reproductive features is provi ded. We concur with earlier suggestions made on the bases of life hist ory and anatomy that the Notheiaceae is the sister group to the Fucale s sensu stricto. Although the issue may never be fully resolved, we su ggest that the evidence points strongly to Notheiaceae being included in the Fucales rather than constituting a separate order.