Validation and phylogenetic placement of the Placentophoraceae fam. nov. (Gigartinales, Rhodophyta)

Abstract

ABSTRACTDespite recent evidence that has shown a close phylogenetic relationship between Callophycus (familia incertae sedis) and the monotypic genus Placentophora (previously regarded as a member of the family Solieriaceae), the phylogenetic relationships of these genera within the order Gigartinales have not been unequivocally established. Although the family name Placentophoraceae was used for Callophycus and Placentophora in 2013, this taxon has yet to be properly validated in accordance with the rules of the International Code of Nomenclature for Algae, Fungi and Plants, thus rendering the Placentophoraceae a nomen nudum. Our present study has generated new rbcL and COI-5P sequences for the generitype species of Placentophora, P. colensoi, and combined them with corresponding data from several species of Callophycus, as well as from other representatives of the Gigartinales, to confirm that Callophycus and P. colensoi form a family-level clade within that order. The exact relationships of this clade to other gigartinalean families, however, is undetermined. In order to validate the Placentophoraceae, a detailed description of the family is supplied, based largely on the most recent molecular, morpho-taxonomic and phytochemical information. The Placentophoraceae are shown to consist of Callophycus (with 10 western Indo-Pacific species, eight of which are limited to Australia) and the monotypic New Zealand genus Placentophora.