Macrocystis is a genus of kelp (large brown algae). This genus contains the largest of all the phaeophyceae or brown algae. Macrocystis has pneumatocysts at the base of its blades. Sporophytes are perennial, and individual stipes may persist for many years. The genus is found widely in subtropical and temperate oceans of the Southern Hemisphere, and in the northeast Pacific from Baja California to Sitka, Alaska. Macrocystis is a major component of kelp forests.