Magniporophytum gen. nov. and Orientalilithon gen. nov. (Hapalidiales, Corallinophycidae): Two new genera of coralline red algae from the Pacific Ocean, including the description of three new species.

We propose, based on a robust set of molecular and morpho-anatomical data of specimens from warm-temperate Japan, two new genera of non-geniculate coralline algae accommodating both attached and rhodolith-forming species: Magniporophytum gen. nov. containing M. variabile sp. nov. (the generitype) and M. epizoicum sp. nov. as well as Orientalilithon gen. nov. containing O. confluens sp. nov. (the generitype) and two undescribed Orientalilithon spp. Our multigene phylogenies inferred from psbA, rbcL, and SSU rDNA gene sequences demonstrated the distinct phylogenetic placements of Magniporophytum and Orientalilithon within the Hapalidiales; however, their generic positions have yet to be confirmed. In the psbA gene analyses, an undescribed Hapalidiales sp. 2 from Canada was separately grouped with the congeners of Magniporophytum from Japan, while an undescribed Lithothamnion sp. 5 from Taiwan was conspecific with Orientalilithon sp. 2 from Japan. Morpho-anatomically, the two new genera share some degrees of overlapping characters but can be distinguished by the shape of epithallial cells and the size of tetra/bisporangial pore openings compared to the surrounding rosette cells in surface view. The new genera differ from other phylogenetically related or morpho-anatomically similar genera by a suite of characters regarding epithallial cells, sub-epithallial initials, and tetra/bisporangial conceptacle characters. Within Magniporophytum, M. variabile and M. epizoicum are barely distinguishable, with a single difference in growth form. This study has highlighted a plausible generic character within the Hapalidiales along with the crypticity of coralline algae at both genus and species ranks and the extended distributions of Magniporophytum and Orientalilithon in the North Pacific Ocean.