any algae of the phylum Phaeophyta, such as the wracks and kelps, which contain a brown pigment in addition to chlorophyll
brown algae in American English
any of a class (Phaeophyceae, division Chromophycota) of large, photosynthetic, marine thallophytic algae, including kelp and fucus, having a brown pigment that obscures the green color of chlorophyll