Molecular phylogenies support taxonomic revision of three species of Laurencia (Rhodomelaceae, Rhodophyta) with the description of a new genus

The systematics of the Laurencia complex was investigated using a taxon-rich data set including the chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) gene only and a character-rich data set combining mitochondrial cytochrome oxidase 1 (COI-5P), the rbcL marker, and the nuclear large subunit of the ribosomal operon (LSU). Bayesian and ML analyses of these data sets showed that three species hitherto placed in the genus Laurencia J.V.Lamour. were not closely related to Laurencia s. str. Laurencia caspica Zinova & Zaberzhinskaya was the sister group of the remaining Osmundea Stackh. species, L. crustiformans McDermid joined Palisada and L. flexilis Setch. consisted of an independent lineage. In light of these results a new genus, Ohelopapa F.Rousseau, Martin-Lescanne, Payri & L.Le Gall gen. nov., is proposed to accommodate L. flexilis. This new genus is morphologically characterized by four pericentral cells in each vegetative axial segment; however, it lacks ‘corps en cerise’ in cortical cells and secondary pit connections between cortical cells, which are characteristic of Laurencia. Three novel combinations are proposed to render the classification closer to a natural system: Ohelopapa flexilis (Setch.) F.Rousseau, Martin-Lescanne, Payri & L.Le Gall comb. nov., Osmundea caspica (Zinova & Zaberzhinskaya) Maggs & L.M.McIvor comb. nov. and Palisada crustiformans (McDermid) A.R.Sherwood, A.Kurihara & K.W.Nam comb. nov