Sargassum muticum, commonly known as Japanese Sargassum, is a cylindrical brown macroalgae that can reach several meters in height. It has an olive green color, with a basal disc that anchors it to the ground and from which its branches extend. These branches have small leaves that decrease in size along the length of the branches, in the axils of the ‘leaves’ have pedunculated aerocysts, alone or in groups. Native to Japan, this species was accidentally introduced to other regions, such as the coast of Europe and North America, where it proliferated significantly, becoming invasive. In Portugal, it occupies a large part of the habitat of the native algae Sargassum vulgare.