Macrocystis pyrifera the “giant kelp,” is a common monospecific brown algae"plant" that can be up to about 200 feet (60 m) tall. It is not a true plant because it lack vascular tissue, roots, flowers, and seeds. It obtains its nutrients by absorbing them. It is the largest of all the kelps. Technically speaking, it is not a plant; rather it is a stramenopile.
It is common along the Pacific Ocean shoreline, from southeastern Alaska to Baja California. In cold, nutrient-rich waters, this kelp can grow at the rate of 2 feet (60 cm) per day, and is one of the fastest growing organisms on Earth. It lives in intertidal to shallow tidal depths. It anchors itself to the sea floor by means of a root-like tangle, called a "holdfast." Gas-filled bladders, located at the base of each leaf-like blade, provide buoyancy so the fronds can float vertically.
Figure 1. A typical kelp growth on the ocean floor, with a scuba diver standing next to, in order to show its relative size. This image was taken at the Aquarium of the Pacific in southern Los Angeles, California.
“Giant kelp forests” provide excellent cover and habitats for numerous kinds of marine animals. It can also be used as food for humans.
The genus is widespread and is found in subtropical, temperate, sub-artic, and sub-anarctic areas: from Alaska to Peru. South Africa, southern Australia, and New Zealand (Wikipedia, 2026).
