Recognition of Rubrointrusa membranacea gen. et comb. nov., Rhodonematella subimmersa gen. et comb. nov. (with a reinterpretation of the life history) and the Meiodiscaceae fam. nov. within the Palmariales (Rhodophyta)

Clayden S.L. and Saunders G.W. 2010. Recognition of Rubrointrusa membranacea gen. et comb. nov., Rhodonematella subimmersa gen. et comb. nov. (with a reinterpretation of the life history) and the Meiodiscaceae fam. nov. within the Palmariales (Rhodophyta). Phycologia 49: 283–300. DOI: 10.2216/09-43.1Two members currently classified in the florideophyte Colaconematales, Colaconema membranaceum and C. subimmersum, display life history and morphological/anatomical characteristics suggestive of some Palmariales, prompting the current investigation. We observed a direct life history by regenerative tetrasporangia for C. membranaceum as previously reported and provide the first evidence of sexual reproduction in C. subimmersum from the Pacific northeast, corroborating reports from Japan. However, the life history pattern in C. subimmersum is reinterpreted as intermediate between that typical of the Palmariaceae and Rhodophysemataceae. We addressed the phylogenetic affinities of these two species by sequencing large-subunit ribosomal DNA and the ‘DNA barcode’ (5′ region of the cytochrome oxidase subunit I gene), which was also used to assess species diversity. In phylogenetic analyses both C. membranaceum and C. subimmersum were unequivocally supported as members of the Palmariales. Colaconema membranaceum displayed a weak affinity for species of Meiodiscus but is distinct in its endozoic basal system, and we propose Rubrointrusa gen. nov., typified by Rubrointrusa membranacea (Magnus) comb. nov. Colaconema subimmersum, consistently grouped with species of Rhodophysema but is divergent from these species in habit, life history, and molecular signature, so that we propose a new monotypic genus Rhodonematella, typified by Rhodonematella subimmersa (Setchell & N.L. Gardner) comb. nov. Rhodonematella, is provisionally placed in the Rhodophysemataceae. We concomitantly examined the phylogenetic affinities of Halosacciocolax kjellmanii and Meiodiscus spp., both tentatively included in the Rhodophysemataceae. Halosacciocolax kjellmanii is retained in the Rhodophysemataceae and transferred to Rhodophysema, Rhodophysema kjellmanii (S. Lund) comb. nov., based on our molecular results and new anatomical observations. Conversely, Meiodiscus species resolved independently of other palmarialean families, and we propose the Meiodiscaceae fam. nov. to accommodate them, as well as Rubrointrusa. Meiodiscus concrescens is restricted to populations from the northeast Pacific; whereas, so-called Atlantic M. concrescens is conspecific with M. spetsbergensis.