A new species, Sargassum boreale Yoshida et Horiguchi is described. It belongs to the subgenus Bactrophycus section Teretia, with cylindrical receptacles and is distinct from Sargassum confusum C. Agardh, S. pallidum (Turner) C. Agardh and Sargassum microceratium (Turner) C. Agardh in having a rather elongated stem with smooth surface and distantly issuing main branches, with narrow leaves. The distinction between S. boreale and these species is also revealed by a difference in internal transcribed spacer 2 (ITS-2) sequences. In addition to the base substitutions, the existence of a large gap in S. boreale distinguishes this species from others. Sargassum boreale is distributed around Hokkaido and Saghalien to 50°N latitude. A key to the species of section Teretia is provided

本文描述了一个新物种Sargassum Boreale Yoshida et Horiguchi.，它属于Bactrophycus亚属的Teretia部分，它具有圆柱形容器，该物种与Sargassum confusum C. Agardh（海蒿子）、S. pallidum(Turner) C. Agardh、和Sargassum microceratium(Turner) C. Agardh不同的是其具有细长的茎干，表面光滑，主枝较远，藻叶窄。S.Boreale和这些物种的区别还表现在内部转录间隔区2(IT-2)序列的差异。除了碱基替换，该物种中存在一个大的间隙（空缺），从而使S.Boreale区别于其他物种。 Sargassum boreale分布在北海道和库页岛到北纬50度的区域。这提供了Teretia部分（研究）的关键物种。

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Sargassum boreale sp. nov. (Fucales, Phaeophyceae) from Hokkaido, Japan