A Revision of the Genus Agarum (Laminariaceae, Phaeophyceae) from the Far Eastern Seas with a Description of Agarum undulatum sp. nov. from the Kuril Islands

A revision of the species composition of the genus Agarum from the Far Eastern seas is based on specimens collected personally by the authors, those deposited at the LE and SAP herbaria, and also obtained during the expeditions of the Zhirmunsky Institute of Marine Biology FEB RAS and SakhalinNIRO to the Kuril Islands. A multigene analysis using the rbcL + cox1 and ITS2 + rbcL+cox1 sequences has shown that the genus Agarum comprises three species. Two of them, A. clathratum Dumortier and A. turneri Postels et Ruprecht, were previously reported from the Asian algal flora. The third species, A. undulatum sp. nov., is here described as new to science. It differs from A. clathratum in ITS2 + rbcL + cox1 by 5.51%; from A. turneri, by 7.5%. The new species, growing in habitats with depths of 15–43 m, is widely distributed in waters along the middle Kuril Islands and the Lesser Kuril Chain. In the phylogenetic tree, A. clathratum splits into two clades, of which one includes specimens belonging to the type form of this species, and the other includes specimens having traits of A. yakishiriense. The difference between the two clades in ITS2 + rbcL + cox1 constitutes only 1.7%. This allows considering A. yakishiriense as a subspecies of A. clathratum. In waters of the Russian Far Eastern seas, it is found in the Sea of Japan and the southern Sea of Okhotsk.