A revised classification of the Dictyoteae (Dictyotales, Phaeophyceae) based on rbcL and 26S ribosomal DNA sequence analyses

Dictyota is a genus of tropical to warm temperate brown algae characterized by parenchymatous, flattened thalli that grow from a single, transversely oriented apical cell. Dictyota is currently distinguished from allied genera of the tribe Dictyoteae (Dilophus, Glossophora, Glossophorella, and Pachydictyon) by the structure of the cortical and medullary layers, as well as the relative abundance of surface proliferations. Even though the traditional classification of the Dictyoteae has repeatedly been criticized in the past, the absence of sound molecular data has so far discouraged any new taxonomic proposals apart from a merger of Dilophus with Dictyota, which has been accepted by only part of the phycological community. Phylogenetic analysis of rbcL gene, partial 26S rDNA sequence, and combined data sets, including four of five generitypes, demonstrates that the traditional classification does not accurately reflect the evolutionary history of the group. None of the genera are resolved as a monophyletic clade. Hence, a merger of Glossophora, Glossophorella, and Pachydictyon in Dictyota is proposed. Two new genera, Canistrocarpus (incorporating D. cervicornis, D. crispata, and D. magneana) and Rugulopteryx (accommodating D. radicans, Dil. suhrii, and Dil. marginata), are proposed. Both genera are supported by molecular indications and a combination of reproductive and vegetative characters. The position of Dil. fastigiatus as a clade sister to Dictyota s.1. and the absence of Dil. gunnianus, the generitype of Dilophus, from the analyses, prevented us from making a more definite statement on the status of the latter genus