Macrocystis

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.

Description
Macrocystis is a genus of kelp, some species of which are so huge that the plants may grow to up to 60m. The stipes arise from a holdfast and branch three or four times from near the base. Blades develop at irregular intervals along the stipe. M. pyrifera grows to over 45 m long. The stipes are unbranched and each has a gas bladder at its base.

Life Cycle
The sporophyte has many sporangia located in its blades, which, through meiosis, releases haploid spores, which will grow into female and male gametophytes. These gametophytes grow through mitosis, and produce gametes, sperm and eggs. The gametophytes are microscopic. The female has larger and fewer cells then the male. The male releases its sperm, which finds its way to the female, following a pheremone released by the female, where it fertilizes the egg, to form the zygote, which, through mitosis, begins growth.

Growth
Juvenile giant kelp grow directly on the parent female gametophyte, extending one or two primary blades, and beginning a rudimentary holdfast, which will eventually cover the gametophyte completely. Growth occurs with lengthening of the stipe, and splitting of the blades. This occurs by means of small tears where the blade meets the stipe, which splits the stipe into two. Pneumatocysts grow after the first few blade splittings.

Ecology
Grows forming extensive beds, large "floating canopies", on a rocky substrate.

Species
There are four species of Macrocystis in the world. Macrocystis angustifolia Bory de Saint-Vincent; M. intergrifolia Bory de Saint-Vincent; M. laevis C.H.Hay; M. pyrifera (L.) C.Ag; and M. pyrifera var. humboldtii Bomplan.

Distribution
Macrocystis pyrifera, giant kelp, is to be found in North America (Alaska to California), South America, South Africa, New Zealand, and southern Australia. Macrocystis integrifolia, a smaller, intertidal species, is found on the Pacific coast of America (British Columbia to California) and South America. M. pyrifera grows to over 45 m long and can do so in one growing season, making it the organism with the fastest linear growth. M. integrifolia is much smaller, the sporangial thalli growing only to 6 m long; it is found on intertidal rocks or shallow subtidal rocks. 

Mycrocystis angustifolia Bory is found in Australia. 

Further reference
Lopez, James. "Macrocystis pyrifera." Monterey Bay Aquarium Research Institute. 2001. Monterey Bay Aquarium Research Institute. 10 Jan 2007

Macrocystis