A new red alga from Japan, Dasya japonovillosa sp. nov. (Delesseriaceae, Ceramiales)

A new red alga from Japan, Dasya japonovillosa, is described. This new species and D. enomotoi, both of which have elongated axes densely covered with numerous soft monosiphonous filaments, may have been misidentified as D. villosa by previous investigators in Japan. Dasya villosa differs from D. japonovillosa and D. enomotoi in the distinct five pericentral cells in transverse sections and palisade‐like tetrasporangial cover cells. The new species is distinguished from several similar species by the combination of the following: an elongated axis (to 65 cm), subdichotomously divided axes and polysiphonous branches, indistinct pericentral cells in transverse sections except near the apices, and the presence of enlarged, inner cortical cells, radially arranged numerous soft monosiphonous filaments, three‐celled carpogonial branches, four tetrasporangia in each fertile segment of the stichidia, and one (rarely two) tetrasporangial cover cell that is not elongated longitudinally and rarely divided transversely.