Molecular phylogeny of small brown algae, with special reference to the systematic position of Caepidium antarcticum (Adenocystaceae, Ectocarpales)

Nuclear ribosomal DNA (3'-SSU, ITS, 5'-LSU) and plastid-encoded (rbcL and R ubisco spacer) sequences were determined in Caepidium antarcticum and compa red to homologous sequences of relatives from Ectocarpales, Scytothamnales, and other brown algae. Plastidial sequences confirmed a previous conclusio n from nuclear ribosomal sequences that some taxa with stellate plastids (A sterocladon and relatives) form the closest outgroup to the Ectocarpales as yet identified. To reconcile nomenclature with the clades resolved in rece nt molecular studies, we propose a subdivision of the Ectocarpales in five families. Plastidial sequences support the recent proposal of Adenocystacea e, and all sequences suggest that Caepidium should be included in this fami ly. As a further result, Geminocarpus was shown to belong to the same clade as Pylaiella and a number of other brown algae with an isomorphic life his tory and discoid plastids. We recognise this clade, whose correct name is A cinetosporaceae, as another family in the Ectocarpales. We also propose to unite a number of genetically related taxa, which were formerly classified in different families, in an extended Chordariaceae. The remaining species of the Ectocarpales belong to Scytosiphonaceae and to Ectocarpaceae, the la tter containing only Ectocarpus and Kuckuckia. (C) 2001 Adac/Editions scien tifiques et medicales Elsevier SAS.