Sargassum muticum is a large brown seaweed. Its lenght varies a lot depending on the growing conditions and the regions where it is found. The stem has regularly alternating branches with flattened oval blades and spherical gas bladders. It attaches to the substrate with a disc-shaped holdfast. S. muticum is an highly distinctive seaweed, with olive-brown color. It is an non-native seaweed, considered an invasive specie.

Pereira,L. Guia Ilustrado das Macroalgas. 2009. Imprensa da Universidade de Coimbra