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Kelps are large seaweeds (algae) belonging to the brown algae (Phaeophyceae) in the order Laminariales. There are about 30 different genera. Kelp grows in "underwater forests" (kelp forests) in shallow oceans, and is thought to have appeared in the Miocene, 23 to 5 million years ago.〔(Macrocystis Evolution )〕 The organisms require nutrient-rich water with temperatures between . They are known for their high growth rate — the genera ''Macrocystis'' and ''Nereocystis'' can grow as fast as half a metre a day, ultimately reaching .〔Thomas, D. 2002. ''Seaweeds.'' The Natural History Museum, London, p. 15. ISBN 0-565-09175-1〕 Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.〔"Kelp," in (''Oxford English Dictionary (Second Edition) ).'' Oxford University Press, 1989. Retrieved 1 December 2006〕 ==Description== In most kelp, the thallus (or body) consists of flat or leaf-like structures known as blades. Blades originate from elongated stem-like structures, the stipes. The holdfast, a root-like structure, anchors the kelp to the substrate of the ocean. Gas-filled bladders (pneumatocysts) form at the base of blades of American species, such as ''Nereocystis lueteana,'' (Mert. & Post & Rupr.)〔 to hold the kelp blades close to the surface. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Kelp」の詳細全文を読む スポンサード リンク
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