A multigene molecular phylogeny of <i>Eisenia</i> reveals evidence for a new species, <i>Eisenia nipponica</i> (Laminariales), from Japan

Recently, synonymizing <i>Eisenia</i> with <i>Ecklonia</i> was suggested based on a molecular phylogeny using the <i>rbc</i>L gene and ITS1–5.8S rDNA sequences. However, in a multigene molecular phylogeny based on mitochondrial <i>cox</i>1, <i>cox</i>3 genes and the <i>atp</i>8–16S rDNA region, as well as the plastid <i>atp</i>B, <i>psa</i>A, <i>psb</i>A and <i>rbc</i>L genes, <i>Ecklonia</i> spp. formed a monophyletic clade supported by high statistical values, and <i>Eisenia</i> spp. showed monophyly depending on analytical methods. The Japanese <i>Eisenia</i> species that used to be identified as <i>Eisenia arborea</i> (<i>E. arborea sensu</i> Arasaki) was shown to be genetically distant from <i>E. arborea</i> from the NE Pacific and <i>E. bicyclis</i> from Japan. <i>Eisenia</i> spp. were morphologically distinct in having a split meristematic zone in the mature thallus forming a dorsi-ventral blade with false branches. Therefore, we propose reinstatement of <i>Eisenia</i> as an independent genus and describe a new species, <i>Eisenia nipponica</i> (= <i>E. arborea sensu</i> Arasaki) from Japan. <i>E. nipponica</i> is distributed on the Pacific Coast of central Honshu, having a separate geographic range from <i>E. bicyclis</i>, which is distributed on the Pacific coast of eastern Honshu and the Sea of Japan coast of north-western Honshu and northern Kyushu.