The Phaeophyceae or brown algae (singular: alga), is a large group of mostly marine

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 multicellular algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

, including many seaweed

Seaweed

Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...

s of colder Northern Hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

 waters. They play an important role in marine environments, both as food and for the habitats they form. For instance Macrocystis

Macrocystis

Macrocystis is a genus of kelp . 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...

, a kelp

Kelp

Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....

 of the order Laminariales, may reach 60 m in length, and forms prominent underwater forests

Kelp forest

Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds....

. Another example is Sargassum

Sargassum

Sargassum is a genus of brown macroalga in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral reefs. However, the genus may be best known for its planktonic species...

, which creates unique habitats in the tropical waters of the Sargasso Sea

Sargasso Sea

The Sargasso Sea is a region in the middle of the North Atlantic Ocean, surrounded by ocean currents. It is bounded on the west by the Gulf Stream; on the north, by the North Atlantic Current; on the east, by the Canary Current; and on the south, by the North Atlantic Equatorial Current. This...

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