XVI International Botanical Congess

Sequences of the ITS region of nrDNA obtained from 16 species representing all 6 genera of Fucaceae (Ascophyllum, Fucus, Hesperophycus, Pelvetia, Pelvetiopsis, Xiphophora) plus one outgroup (Hormosira) indicate that the Fucaceae are monophyletic, although the northern hemisphere taxa are highly divergent from the only southern hemisphere genus, Xiphophora. Pelvetia is not monophyletic. Fucus is monophyletic and not ancestral in Fucaceae. ITS sequences identified two lineages within Fucus, one with F. serratus sister to the clade containing F. gardneri, F. distichus, and F. evanescens, and a second including F. vesiculosus, F. spiralis, F. ceranoides and F. virsoides. These results show that the reproductive ecology of the Fucaceae has followed evolutionary trends that are distinct from those proposed by previous models, in particular 1) number of eggs per oogonium has not followed a gradual reduction and 2) monoecy/dioecy has changed several times during evolution of this family.