Brown algae

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iBrown algae

Pacific Rockweed (Fucus distichus) in Olympic National Park

Scientific classification

Kingdom:	Protista
Division:	Heterokontophyta
Class:	Phaeophyceae Kjellman

Orders

Ascoseirales
Chordariales
Cutleriales
Desmarestiales
Dictyosiphonales
Dictyotales
Ectocarpales
Fucales
Laminariales (kelps)
Scytosiphonales
Scytothamnales
Sphacelariales
Sporochnales
Syringodermatales
Tilopteridales

The Phaeophyta or the brown algae are a large group of multicellular, mostly marine, algae, including many notable seaweeds of colder Northern Hemisphere waters. They play an important role in marine environments both as food, and for the habitats they can form. For instance Macrocystis, a member of the Laminariales or kelps, may reach 60 meters in length, and forms prominent underwater forests. Another notable example is Sargassum, which creates unique habitats in the tropical waters of the Sargasso Sea. This is one of the few areas where a large biomass of brown algae may be found in tropical waters. Many brown algae such as members of the order Fucales (the rockweeds) are commonly found along rocky seashores. Some members of the division are used as food for humans.

Brown algae belong to a very large group called the hererokonts. Most contain the pigment fucoxanthin, which is responsible for the distinctive greenish-brown color that gives brown algae their name. Brown algae are unique among heterokonts in developing into multicellular forms with differentiated tissues, but they reproduce by means of flagellate spores, which closely resemble other heterokont cells. Genetic studies show their closest relatives are the yellow-green algae.