Phaeophyta (brown algae) A division of algae which includes no single-celled species; almost all are marine, growing mostly in the intertidal regions (but species of Bodenella and Heribaudiella occur in fresh water). They are the dominant seaweeds in the colder waters of the northern hemisphere. They are typically olive-brown or greenish in colour (at least when wet) owing to the presence of the pigment fucoxanthin in the chloroplasts. There are at least 13 orders, and many genera.

Phaeophyta (brown algae) A phylum of algae in which the green chlorophyll pigments are usually masked by the brown pigment fucoxanthin. Brown algae are usually marine (being abundant in cold water) and many species, such as the wracks (Fucus), inhabit intertidal zones. They vary in size from small branched filaments to ribbon-like bodies (known as kelps) many metres long.