High Quality Content by WIKIPEDIA articles! Macrocystis is a genus of kelp (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. Common along the coast of the eastern Pacific Ocean, from central California to Baja California and north to southeast Alaska (Sitka).