Seaweed

Seaweed is macroscopic algae that grow in marine or brackish waters. It includes red, green, and brown algae, which are distinct evolutionary groups rather than one lineage.

Brown algae: A group of mostly marine algae that includes kelps and other large seaweeds. This group includes many familiar large seaweeds, especially kelps.
Holdfast: A structure that anchors an alga or other organism to a surface. Many seaweeds use holdfasts to stay attached to rocks or other substrates.
Nori: Dried sheets of edible red algae, commonly used in Japanese cuisine. Nori is a widely eaten seaweed product made from red algae.
Kelp forest: A marine ecosystem formed by dense stands of large brown algae, especially kelps. Kelp forests are habitat-rich ecosystems built by seaweed growth.
Red algae: A diverse group of algae whose pigments allow many species to live in deeper water. Red algae form one of seaweed’s three major groups and include edible nori.
Bladderwrack: A brown seaweed with air-filled bladders that help its fronds float near the water surface. Its air bladders show how some seaweeds position photosynthetic tissue in the water.
Agar: A gel-forming substance extracted mainly from red algae and used in food and laboratory media. Red seaweeds supply agar, a valuable thickener and culture medium.
Seagrass meadow: A coastal ecosystem of flowering plants adapted to grow submerged in seawater. Seagrass meadows resemble seaweed beds but are formed by true plants, not algae.
Green algae: A diverse group of photosynthetic organisms that includes seaweeds and the ancestors of land plants. Some marine green algae grow into conspicuous seaweeds, despite their closer relationship to land plants.
Isomorphic alternation of generations: A life cycle in which haploid and diploid generations look alike. Some seaweeds alternate between generations that are difficult to distinguish by appearance.

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