MOLECULAR AND MORPHOLOGICAL INVESTIGATIONS OF 3 BROWN ALGAL GENERA WITH STELLATE PLASTIDS - EVIDENCE FOR SCYTOTHAMNALES ORD. NOV. (PHAEOPHYCEAE)

Recent molecular phylogenies of the Phaeophyceae have demonstrated tha t the morphologically simple ephemeral species referred to as Ectocarp ales sensu Into are not primitive in a phylogenetic sense. They form a monophyletic group and share parietal plastids with pyrenoids. The cl ade is distant from the orders of morphologically advanced brown algae with discoid plastids and no or reduced pyrenoids. Sequences of parts of the nuclear ribosomal cistron of species of the genera Scytothamnu s Stereocladon, and Splachnidium, which have stellate chloroplasts wit h a single pyrenoid in the center of the cells, provide strong evidenc e that none of these algae belong to the Ectocarpales sensu lato. Neit her do they group with the Fucales. with which Splachnidium shares rec eptacles and conceptacles. Although an analysis of small subunit seque nces fails to clearly separate them from the Laminariales, with which they do not share morphological, cytological, or reproductive characte rs, a combined analysis of partial small subunit sequences and more co nserved parts of the otherwise highly variable internal transcribed sp acers (ITS1 and ITS2) places them between Laminariales and Ectocarpale s sensu late. We propose Scytothamnales ord. nov. with the two closely related genera Scytothamnus and Stereocladon in the family Scytothamn aceae and the more distant Splachnidium in its own monotypic family. A denocystis utricularis (Bory) Skottsberg, which previously has been in cluded in Scytothamnaceae despite its different, discoid plastid type, remains a member of Ectocarpales sensu into.