Kelp transcriptomes provide robust support for interfamilial relationships and revision of the little known Arthrothamnaceae (Laminariales).

If ever there were "charismatic megaflora" of the sea, the Laminariales (kelp) would undoubtedly meet that designation. From the Northeast Pacific kelp forests to the less diverse, but nonetheless dense, kelp beds ranging from the Arctic to the cold temperate waters of the Southern Hemisphere, kelp provide habitat structure and food for a variety of productive marine systems. Consequently, kelp are well represented in the literature, however, understanding their evolution has proven challenging. We used a 152-gene phylogenomics approach to better resolve the phylogeny of the "derived" kelp families (viz., Agaraceae, Alariaceae, Laminariaceae, and Lessoniaceae). The formerly unresolved Egregia menziesii firmly joined a significantly expanded Arthrothamnaceae including Arthrothamnus, Cymathaere, Ecklonia, Macrocystis, Nereocystis, Pelagophycus, Postelsia, Pseudolessonia, Saccharina, and Streptophyllopsis, which rendered both the Laminariaceae and Lessoniaceae monogeneric. A published eight-gene alignment, the most marker-rich prior to this study, was expanded and analyzed to facilitate inclusion of Aureophycus. Although the topology was unchanged at the family level between the transcriptome data set relative to eight-gene analyses, the superior resolving power of the former was clearly established.