Molecular phylogeny of the Dictyotales and their position within the Phaeophyceae, based on nuclear, plastid and mitochondrial DNA sequence data.

For the first time, on the basis of nuclear, plastid and mitochondrial sequence data, the most comprehensive molecular phylogeny of the Dictyotales to date is presented, in a broad context where all brown algal orders are included (except Discosporangiales, Ascoseirales and Nemodermatales). A veto supertree approach was used here to evaluate congruency and conflicts between genes: phylogenetic signal was congruent and mainly carried by chloroplastic information. Supermatrix analyses (BI, ML and MP) revealed that Dictyotales is sister to Onslowiales, this ensemble being sister of a clade also encompassing Sphacelariales and Syringodermatales. The family Scoresbyellaceae is merged into the family Dictyotaceae. Furthermore, the current subdivision of the Dictyotaceae into two tribes was not supported. The enigmatic genus Stoechospermum was shown to belong to the same clade as Dictyota, Rugulopteryx, Scoresbyella and Canistrocarpus. Homoeostrichus and Dictyopteris did not appear monophyletic. Zonaria stipitata clustered with the Spatoglossum species; since this is consistent with its morphological features, the new combination Spatoglossum stipitatum is proposed accordingly.

A comprehensive phylogeny of the Phaeophyceae based on nrDNA sequences resolves the earliest divergences.

The present study is the first comprehensive phylogeny of the class of the Phaeophyceae. For 67 species representing all orders of the class, the sequences of the 3'-end of the small and the 5'-end of the large subunit nrRNA genes were aligned and analysed. A further analysis based on sequences of the 3'-end of the small and of the complete sequences of the 28S gene of the large subunits was also performed, but for only eight taxa. In both analyses, Tribonema marinum (Xanthophyceae) was used as outgroup. The analyses showed the Dictyotales as diverging first, followed by the Sphacelariales, then the Syringodermatales. Most of the orders currently accepted were confirmed as monophyletic groups but the Laminariales and Tilopteridales remained polyphyletic. The relationships of the remaining orders to each other were not resolved with the present data set. Ascoseira, included for the first time in a molecular study, appeared as a separate lineage without any clear relationship with other algae possessing conceptacles (Splachnidium and Fucales). Algae with stellate plastids, never studied in a global context, were polyphyletic; this result is consistent with their plastid ultrastructure and is discussed in detail. As further result of the present study, the South African genus Bifurcariopsis appeared as the sister taxon of the North Atlantic genus Himanthalia, and Xiphophora appeared as the sister taxon of Hormosira rather than as a member of the Fucaceae; the taxonomic position of these genera is discussed.

Low divergence in rDNA ITS sequences among five species of Fucus (Phaeophyceae) suggests a very recent radiation.

Sequences from the two ribosomal DNA internal transcribed spacers (ITS1 and ITS2) were compared among five species of Fucus. Based on the present taxon sampling, parsimony analysis showed that Fucus serratus is the sister-group of the remaining Fucus species when Ascophyllum nodosum was used as an outgroup. The topology of the tree was (Fucus serratus (F. lutarius (F. vesiculosus (F. spiralis + F. ceranoides)))). The extremely low variation observed suggests a very recent radiation of the genus which supports the view widely accepted that the Fucales are among the most evolutionarily advanced of the brown algae. We further note that sequence differences between Fucus and Ascophyllum were 28%: this does not rule out the utility of ITS sequences within the Fucaceae. The very low number of informative positions allows to demonstrate empirically that distance matrix methods group on the basis of symplesiomorphies.