Brown algae

Phylum: Heterokontophyta
Class: Phaeophyceae

Brown algae contain most of the large conspicuous algae seen on rocky shorelines and in shallow waters. Brown algae are the heaviest and largest seaweeds, and the fastest growing of all the algae. Almost wholly restricted to the marine environment, they are generally shades of brown, except for some that can appear blue underwater. Nearly all species of brown algae remain fastened on rocky or other firm habitats by a holdfast, although some species are free-floating.