A new variety of Sargassum miyabei Yendo, Sargassum miyabei var. okiense nov. (Sargassaceae, Phaeophyta) is described from the Oki Islands, the Sea of Japan.
This new variety is usually 1-3.7 m in length of thallus, provided with crookednesses and spiral twists in the principal branch, male receptacles of 3-18 mm, 0.5-1 mm in length and diameter, and the female receptacles of 3-11 mm, 0.5-1 mm in length and diameter.
Key Index Words; Phaeophyta, Sargassaceae, Sargassum miyabei var. oliense, the Sea of Japan.