2015 Volume 8 Issue 1 Pages 1-10
Sargassum glaucescens is distributed in the tropical and subtropical regions in the western Pacific including Japan and Southeast Asian countries. In Japan, this species was first reported in 1993, inhabiting the coastal zone of Shimaura Island, Miyazaki Prefecture. However, the morphological description of this species, in addition to its distribution in Japan, has remained unclear, due to limited subsequent reports. Between 2004 and 2013, we collected specimens of a species resembling S. glaucescens from southern Japan, to clarify the status of this species in Japan using both morphological and molecular diagnostic techniques. The specimens examined in this study exhibited the following morphological characteristics of S. glaucescens : (1) terete or slightly compressed main branches with a smooth surface, which extend from a short stem with a holdfast ; (2) linear oblong to lanceolate shaped leaves ; (3) spherical-shaped vesicles with a round apex ; (4) slightly compressed dioecious receptacles with zygocarpic characters. Moreover, we determined the nucleotide sequences of specimens collected from several sites around Japan, and compared them with morphologically closely related species. The results of both the morphological and molecular analyses indicated that the specimens examined in this study were S. glaucescens, and that at present, it is one of the dominant species in southern Japan.