Brown algae 233271 221458260 2008-06-24T16:14:20Z Smith609 846901 {{Taxobox |fossil_range=Jurassic - recent | name = Brown algae | image = pacific rockweed, Olympic National Park, USA.jpg | image_width = 250px | image_caption = [[Pacific rockweed]] (''[[Fucus distichus]]'') in [[Olympic National Park]] | domain = [[Eukaryota]] | regnum = [[Chromalveolata]] | phylum = [[Heterokont]]ophyta | classis = '''Phaeophyceae''' | classis_authority = [[Frans Reinhold Kjellman|Kjellman]] }} The '''Phaeophyceae''' or '''brown algae''', (singular: alga) is a large group of mostly [[Ocean|marine]] multicellular [[alga]]e, including many [[seaweed]]s of colder [[Northern Hemisphere]] waters. They play an important role in marine environments both as food, and for the habitats they form. For instance ''[[Macrocystis]]'', a member of the [[Laminariales]] or [[kelp]]s, may reach 60&nbsp;[[metre|m]] in length, and forms prominent underwater [[kelp forest|forests]]. Another 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 [[Tropics|tropical waters]]. Many brown algae such as members of the order [[Fucales]] are commonly found along rocky seashores. Some members of the division are used as food for humans. Worldwide there are about 1500-2000 brown seaweed [[species]].<ref name="Thomas 02" >'''Thomas,D.N.''' 2002. ''Seaweeds.'' The Natural History Museum, London. ISBN 0 56509175 1</ref> Brown algae belong to a very large group, the [[Heterokont|Heterokontophyta]], a eukaryotic group of organisms distinguished most prominently by having [[chloroplasts]] surrounded by four membranes, suggesting an origin from a symbiotic relationship between a basal eukaryote and another eukaryotic organism. 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 heterokonts in developing into multicellular forms with [[Cellular differentiation|differentiated]] [[Biological tissue|tissues]], but they reproduce by means of [[Flagellum|flagellate]] [[spore]]s, which closely resemble other heterokont cells. Genetic studies show their closest relatives to be the [[yellow-green algae]]. Phaeophyta first appear in the [[fossil]] record in the [[Mesozoic]], possibly as early as the [[Jurassic]]. Their occurrence as fossils is rare due to their generally soft-bodied habit, and scientists continue to debate the identification of some finds. Other algae groups, such as the [[Red Algae|red algae]] and [[Green Algae|green algae]] have a number of [[calcareous]] members, which are more likely to leave evidence in the [[fossil]] record than the soft bodies of the brown algae. [[Miocene]] fossils of a soft-bodied brown macro algae, ''[[Julescrania]]'', have been found well-preserved in [[Monterey Formation]] [[diatomite]]s, but few other certain fossils, particularly of older specimens are known in the fossil record.<ref>{{cite journal|last = '''Coyer|first = J.A. |coauthors = G.J. Smith, R.A. Anderson'''|title = Evolution of ''Macrocystis'' spp. (Phaeophyta) as determined by ITS1 and ITS2 sequences|journal = Journal of Phycology|volume = 37|pages = 574–585|publisher = Blackwell Publishing|date = 2001|doi = 10.1046/j.1529-8817.2001.037001574.x}}</ref>[http://www.ucmp.berkeley.edu/chromista/browns/phaeofr.html] == Taxonomy == This is a list of the [[Order (biology)|orders]] in the class Phaeophyceae:<ref>{{cite web |author='''Guiry, M. D. & G. M. Guiry''' |year=2006 |title=AlgaeBase version 4.2 |publisher=[[National University of Ireland]], Galway |url=http://www.algaebase.org/taxonomy.lasso?id=4360&-session=abv3:48E46E6A1d71e0CB2DjYi1914543 |accessdate=7 December |accessyear=2006}}</ref> * [[Ascoseirales]] <small>Petrov</small> * [[Choristocarpales]] * [[Cutleriales]] <small>Oltmanns</small> * [[Desmarestiales]] <small>Setchell & Gardner</small> * [[Dictyotales]] <small>[[Frans Reinhold Kjellman|Kjellman]]</small> * [[Ectocarpales]] <small>Setchell & Gardner</small> * [[Fucales]] <small>Kylin</small> * [[Ishigeales]] * [[Laminariales]] <small>Migula</small> * [[Ralfsiales]] <small>Nakamura</small> * [[Scytothamnales]] <small>A. F. Peters & M. N. Clayton</small> * [[Sphacelariales]] <small>Oltmanns</small> * [[Sporochnales]] <small>Sauvageau</small> * [[Syringodermatales]] <small>E. C. Henry</small> * [[Tilopteridale]] <small>Bessey</small> A few species, such as ''[[Botrydium stoloniferum]]'', are placed ''[[incertae sedis]]'', or of uncertain position, as to order in this classification scheme. ==Life cycle== The life cycle shows great variability from one group to another. However the life cycle of ''[[Laminaria]]'' consists of the [[diploid]] generation, that is the large plant well know to most people. It produces sporangia from specialised microscioic structures, these divide meiotically ([[meiosis]]) before they are released. As they are [[haploid]] there are equal numbers of male and female spores.<ref name="Thomas 02"/> With the exception of the Fucales all brown algae have a life cycle which consists of an alternation between morphologically haploid and diploid plants referred to as Monomorphic. A dimorphic life cycle consists of an alteration between dissimilar haploid and diploid plants. <ref name="Fletcher 87">'''Fletcher,R.L.''' 1987. ''Seaweeds of the British Isles.'' Volume '''3'''. Part 1. British Museum (Natural History), London. ISBN 0 565 00992 3</ref> == Adaptations == Brown algae have adapted to a wide variety of marine ecological niches including the tidal splash zone, rock pools, the whole intertidal zone and relatively deep near shore waters. However they are predominantly cool and cold water organisms that benefit from nutrients in up welling cold water currents and inflows from land; ''Sargassum'' being an obvious exception to this generalisation. ==References== <references/> ==Further reading== Druehl, L.D. 1988. Cultivated edible kelp. ''in'' ''Algae and Human Affairs.'' Lembi, C.A. and Waaland, J.R. (Editors) 1988.ISBN 0 521 32115 8. ==See also== * [[Cyanobacteria]] * [[Diatom]] * ''[[Fucus]]'' * [[Golden algae]] * [[Green algae]] * [[Kelp]] * ''[[Ascophyllum nodosum]]'' (Knotted wrack) * ''[[Laminaria]]'' * [[Red algae]] * ''[[Sargassum]]'' * [[Yellow-green algae]] * [[List of brown algal genera]] * [[Wrack (science)]] * [[Turbinaria ornata]] ==External links== * [http://www.mbari.org/staff/conn/botany/flora/browns.htm Monterey Bay Flora] * [http://seaweed.ucg.ie/algae/phaeophyta.lasso Phaeophyceae], [[National University of Ireland, Galway]] {{commonscat|Phaeophyceae}} [[Category:Algae]] [[Category:Biological oceanography]] [[Category:Brown algae| ]] [[Category:Chromista]] [[Category:Heterokonts]] [[bg:Кафяви водорасли]] [[cs:Chaluhy]] [[da:Brunalge]] [[de:Braunalgen]] [[et:Pruunvetikad]] [[es:Phaeophyceae]] [[eo:Brunalgoj]] [[fr:Phaeophyceae]] [[hr:Smeđe alge]] [[id:Ganggang coklat]] [[it:Phaeophyta]] [[he:חומיות (אצות)]] [[lt:Rudadumbliai]] [[hu:Barnamoszatok]] [[mk:Кафеави алги]] [[ja:褐藻]] [[no:Brunalger]] [[pl:Brunatnice]] [[pt:Phaeophyta]] [[simple:Brown algae]] [[sr:Mrke alge]] [[fi:Ruskolevät]] [[sv:Brunalger]] [[zh:褐藻纲]]