[5] The genus is found widely in subtropical, temperate, and sub-Antarctic oceans of the Southern Hemisphere and in the northeast Pacific.

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.

[12] The smaller morphs, formerly identified as Macrocystis integrifolia, have deep brown color on flattened rhizomes which are profusely dichotomously branched.

These blades bear various sori containing sporangia, which release haploid spores, which will grow into microscopic female and male gametophytes.

The Macrocystis sperm consists of biflagellate non-synthetic antherozoids, which find their way to the oogonia following the lamoxirene.

To establish itself, a young kelp produces one or two primary blades, and begins a rudimentary holdfast, which serves to anchor the plant to the rocky bottom.

[citation needed] Growth occurs with lengthening of the stipe (central stalk), and splitting of the blades.

At the growing tip is a single blade, at the base of which develop small gas bladders along one side.

[7][27]: 226–227 Macrocystis typically grow forming extensive beds, large "floating canopies", on rocky substrata between the low intertidal.

[31][32] Where surface waters are poor in nutrients, nitrogen in the form of amino acids is translocated up the stipe through sieve elements that very much resemble the phloem of vascular plants.

[35] In 2009 and 2010, however, two studies that used both morphological[36] and molecular[3] assessments demonstrate that Macrocystis is monospecific (as M. pyrifera), which is currently accepted by the phycological community (see AlgaeBase).

[16] Macrocystis pyrifera has been utilized for many years as a food source;[42][43] it also contains many compounds such as iodine, potassium, other minerals vitamins and carbohydrates and thus has also been used as a dietary supplement.

[43] The demand for M. pyrifera is increasing due to the newfound uses of these plants such as fertilizers, cultivation for bioremediation purposes, abalone and sea urchin feed.

[49] In recent years, the kelp forests have decreased dramatically throughout Japan, Chile, Korea, Australia and North America.

This has been known to kill off M. pyrifera, due to its need for cold waters it would usually find in the North Pacific Ocean.

[52] In California, El Niño also brought along a population bloom of purple sea urchins which feed on the giant kelp.

[53] Off the coast of Tasmania, kelp forests have been significantly affected by several factors, including warming waters, shifting of the East Australian current (EAC), and invasion of long-spine sea urchins.

Locals have noticed significant effects on the population of abalone, a food source for the Aboriginal Tasmanians for thousands of years.

[55] Some of this loss was attributed by locals to the harvesting of the forests by Alginates Australia, which opened its factory near Triabunna in 1963, shutting down operations 10 years later as uneconomical.

Methods include artificial reefs, reducing numbers of purple sea urchins in overpopulated areas, and planting roots along the ocean floor.

[50] Scientists had built 28 artificial reefs off Maria Island by 2019, and were hopeful of bringing the kelp forests back.