Evolution of the Fucaceae (Phaeophyceae) inferred from nrDNA-ITS

Sequences of the internal transcribed spacer region (ITS-1, 5.8S, and ITS-2 ) of nuclear ribosomal DNA were obtained from 16 species representing all s ix genera of Fucaceae (Ascophyllum, Fucus, Hesperophycus, Pelvetia, Pelveti opsis, and Xiphophora) plus one outgroup (Hormosira), Parsimony analysis in dicated that the family Fucaceae is monophyletic and that the northern hemi sphere taxa are highly divergent from the only southern hemisphere genus, X iphophora, The genus Pelvetia is not monophyletic because the European P, c analiculata is more closely related to Fucus, Hesperophycus and Pelvetiopsi s than to other Pelvetia species. We establish Silvetia, gen, nov. and tran sfer the 3 Pacific species of Pelvetia to the new genus. Fucus is monophyle tic and not ancestral in the Fucaceae, The ITS sequences identified two str ongly supported lineages within Fucus, one with F. serratus sister to the c lade containing F, gardneri, F, distichus, and F, evanescens and a second i ncluding F, vesiculosus, F, spiralis, F, ceranoides, and F, virsoides, The ITS was not useful for resolving relationships within each of these cluster s and between populations of F, vesiculosus, Within-individual variation in ITS sequences is high in Fucus, a derived genus, compared to Ascophyllum, a more ancestral genus. Mapping of the two characters that form the basis o f Powell's model for speciation in the Fucaceae showed that 1) number of eg gs per oogonium has not followed a gradual reduction and that 2) monoecy/di oecy has changed several times during evolution of this family.