Editing Brown algae (section)

{{short description|Large group of multicellular algae, comprising the class Phaeophyceae}}
{{Use dmy dates|date=October 2023}}
{{Automatic taxobox
| fossil_range = [[Late Jurassic]] to present {{fossil range|150|0|ref=<ref name=Medlin1997/><ref name="Lim1986"/>}}
| image = Kelp-forest-Monterey.jpg
| image_caption = Giant kelp (''[[Macrocystis pyrifera]]'')
| image_alt = Giant kelp (Macrocystis pyrifera)
| display_parents = 3
| taxon = Phaeophyceae
| authority = [[Frans Reinhold Kjellman|Kjellman]], 1891<ref>{{cite book
|last=Kjellman |first=F. R.
|year=1891
|chapter=Phaeophyceae (Fucoideae)
|editor1-last=Engler |editor1-first=A.
|editor2-last=Prantl |editor2-first=K.
|title=Die natürlichen Pflanzenfamilien
|volume=1 |issue=2 |pages=176–192
|location=Leipzig
|publisher=[[Wilhelm Engelmann]]}}</ref>
| subdivision_ranks = Orders
| subdivision = See [[#Classification|classification]]
| synonyms =
* Fucophyceae <small>[[Eugenius Warming|Warming]], 1884</small>
* Melanophyceae <small>[[Gottlob Ludwig Rabenhorst|Rabenhorst]], 1863</small>
* Phaeophyta <small></small>
}}

'''Brown algae''' ({{singular}}: '''alga''') are a large group of [[multicellular]] [[algae]] comprising the [[class (biology)|class]] '''Phaeophyceae'''. They include many seaweeds located in colder waters of the [[Northern Hemisphere]]. Brown [[algae]] are the major [[seaweeds]] of the temperate and polar regions. Many brown algae, such as members of the order [[Fucales]], commonly grow along rocky seashores. Most brown algae live in marine environments, where they play an important role both as food and as a potential [[habitat]]. For instance, ''[[Macrocystis]]'', a [[kelp]] of the order [[Laminariales]], may reach {{cvt|60|m|ft}} in length and forms prominent underwater [[kelp forest]]s that contain a high level of biodiversity.<ref name="Cock-2011">{{Cite journal|last1=Cock|first1=J. Mark|last2=Peters|first2=Akira F.|last3=Coelho|first3=Susana M.|date=9 August 2011|title=Brown algae|journal=Current Biology|volume=21|issue=15|pages=R573–R575|doi=10.1016/j.cub.2011.05.006|pmid=21820616|doi-access=free}}</ref> Another example is ''[[Sargassum]]'', which creates unique floating mats of seaweed in the tropical waters of the [[Sargasso Sea]] that serve as the habitats for many species. Some members of the class, such as kelps, are used by humans as food.

Between 1,500 and 2,000 [[species]] of brown algae are known worldwide.<ref>{{Cite book |url=https://books.google.com/books?id=s1P855ZWc0kC&pg=166 |title=Algae: an introduction to phycology |last1=Hoek |first1=Christiaan |last2=den Hoeck |first2=Hoeck Van |last3=Mann |first3=David |last4=Jahns |first4=H.M. |date=1995 |publisher=Cambridge University Press |isbn=9780521316873 |oclc=443576944 |page=166 |access-date=26 April 2018 |archive-date=16 October 2023 |archive-url=https://web.archive.org/web/20231016191928/https://books.google.com/books?id=s1P855ZWc0kC&pg=166#v=onepage&q&f=false |url-status=live }}</ref> Some species, such as ''[[Ascophyllum nodosum]]'', have become subjects of extensive research in their own right due to their commercial importance. They also have environmental significance through [[carbon fixation]].<ref name="Cock-2011" />

Brown algae belong to the [[Stramenopile]]s, a [[clade]] of [[Eukaryote|eukaryotic]] organisms that are distinguished from [[Viridiplantae|green plants]] by having [[chloroplast]]s surrounded by four membranes, suggesting that they were acquired secondarily from a [[symbiotic relationship]] between a basal eukaryote and a red or green alga. Most brown algae contain the pigment [[fucoxanthin]], which is responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among Stramenopiles in developing into multicellular forms with [[Cellular differentiation|differentiated]] [[Tissue (biology)|tissues]], but they reproduce by means of [[Flagellum|flagellated]] [[spore]]s and [[gamete]]s that closely resemble cells of single-celled Stramenopiles. Genetic studies show their closest relatives to be the [[yellow-green algae]].