Brown algae are included under
Cyanophyceae are blue-green algae and not brown. Bacillariophyceae is a very common phytoplankton, but does not belong to the group of brown algae. Rhodophyceae is red algae and not brown. The Phaeophyceae is brown algae, of mostly marine multicellular algae, including many types of seaweed. They play an important role in marine environments, both as food and for the habitats they form. Some of them may extend to large areas and form underground forests. Sargassum, creates unique habitats in the tropical waters of the Sargasso Sea. Many brown algae, grow along rocky seashores like members of Fucales. Some brown algae such as kelp are used as food by humans. Thus, the correct answer is option C.