Macrocystis pyrifera, commonly known as giant kelp or giant bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus Macrocystis. Giant kelp is common along the coast of the easternPacific Ocean, from Baja California north to southeast Alaska, and is also found in the southern oceans nearSouth America, South Africa, and Australia. Individual algae may grow to more than 45 metres (148 ft) long at a rate of as much as 2 feet (61 cm) per day. Giant kelp grows in dense stands known as kelp forests, which are home to many marine animals that depend on the algae for food or shelter. The primary commercial product obtained from giant kelp is alginate, but humans also harvest this species on a limited basis for use directly as food, as it is rich in iodine, potassium, and other minerals. It can be used in cooking in many of the ways other sea vegetables are used, and particularly serves to add flavor to bean dishes.

M. pyrifera is the largest of all algae. The stage of the life cycle that is usually seen is the sporophyte, which is perennial and individuals persist for many years.The giant kelp receives its name from its incredible size. Individuals may grow to up to 50 metres (160 ft) long or more. The kelp often grows even longer than the distance from the bottom to the surface as it will grow in a diagonal direction due the ocean current pushing against the kelp.^[2] The stalks arise from a holdfast and branch three or four times from near the base. Blades develop at irregular intervals along the stipe, with a single pneumatocyst (gas bladder) at the base of each blade.^[3]

A related and similar-looking, but smaller species, M. integrifolia, grows to only to 6 metres (20 ft) long. It is found on intertidal rocks or shallow subtidal rocks along the Pacific coast of North America (British Columbia toCalifornia) and South America.^[4][5]

(From Wikipedia, August 2015)