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

Abstract

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.