Editing Brown algae (section)

==Evolutionary history==

Genetic and ultrastructural evidence place the Phaeophyceae among the [[heterokont]]s (Stramenopiles),<ref name="pmid16248873">{{cite journal
|last=Adl
|first=S. M.
|year=2005
|title=The new higher level classification of eukaryotes with emphasis on the taxonomy of protists
|url=http://www.vliz.be/imisdocs/publications/233133.pdf
|journal=[[Journal of Eukaryotic Microbiology]]
|volume=52
|issue=5
|pages=399–451
|doi=10.1111/j.1550-7408.2005.00053.x
|pmid=16248873
|display-authors=etal
|doi-access=free
|access-date=27 August 2012
|archive-date=29 May 2013
|archive-url=https://web.archive.org/web/20130529063517/http://www.vliz.be/imisdocs/publications/233133.pdf
|url-status=live
}}</ref> a large assemblage of organisms that includes both [[photosynthesis|photosynthetic]] members with [[plastid]]s (such as the [[diatom]]s) as well as non-photosynthetic groups (such as the [[slime net]]s and [[Oomycete|water mold]]s). Although some heterokont relatives of the brown algae lack plastids in their cells, scientists believe this is a result of evolutionary loss of that organelle in those groups rather than independent acquisition by the several photosynthetic members.<ref name="Lane2008">{{cite journal
|last1=Lane
|first1=C. E.
|last2=Archibald
|first2=J. M.
|year=2008
|title=The eukaryotic tree of life: Endosymbiosis takes its TOL
|url=http://www.vliz.be/imisdocs/publications/135930.pdf
|journal=[[Trends in Ecology and Evolution]]
|volume=23
|issue=5
|pages=268–275
|doi=10.1016/j.tree.2008.02.004
|pmid=18378040
|citeseerx=10.1.1.555.2930
|access-date=27 August 2012
|archive-date=20 June 2013
|archive-url=https://web.archive.org/web/20130620111315/http://www.vliz.be/imisdocs/publications/135930.pdf
|url-status=live
}}</ref> Thus, all heterokonts are believed to descend from a single [[heterotrophic]] ancestor that became photosynthetic when it acquired plastids through [[endosymbiosis]] of another unicellular eukaryote.<ref name="Hoek">{{cite book|title=Algae: An Introduction to Phycology|last1=van den Hoek|first1=C.|last2=Mann|first2=D. G.|last3=Jahns|first3=H. M.|publisher=[[Cambridge University Press]]|year=1995|isbn=978-0-521-31687-3|location=Cambridge|pages=165–218}}</ref>

The closest relatives of the brown algae include unicellular and filamentous species, but no unicellular species of brown algae are known. However, most scientists assume that the Phaeophyceae evolved from unicellular ancestors.<ref>
{{cite book
|last=Niklas |first=K. J.
|year=1997
|title=The Evolutionary Biology of Plants
|page=156
|location=Chicago
|publisher=[[University of Chicago Press]]
|isbn=978-0-226-58082-1
}}</ref> [[DNA]] sequence comparison also suggests that the brown algae evolved from the filamentous [[Phaeothamniophyceae]],<ref name="Lee2008">
{{Cite book
|last=Lee
|first=R. E.
|year=2008
|title=Phycology
|edition=4th
|publisher=[[Cambridge University Press]]
|isbn=978-0-521-63883-8
|url-access=registration
|url=https://archive.org/details/phycology00robe
}}</ref> [[Xanthophyceae]],<ref name="Ariztia1991">
{{cite journal
|last1=Ariztia |first1=E. V.
|last2=Andersen |first2=R. A.
|last3=Sogin |first3=M. L.
|year=1991
|title=A new phylogeny of chromophyte algae using 16S-like rRNA sequences from ''Mallomonas papillosa'' (Synurophyceae) and ''Tribonema aequale'' (Xanthophyceae)
|journal=[[Journal of Phycology]]
|volume=27 |issue=3 |pages=428–436
|doi=10.1111/j.0022-3646.1991.00428.x
|s2cid=84693030
}}</ref> or the [[Chrysophyceae]]<ref name="Taylor1993">
{{cite book
|last1=Taylor |first1=T. N.
|last2=Taylor |first2=E. L.
|year=1993
|title=The Biology and Evolution of Fossil Plants
|pages=128–131
|location=Englewood Cliffs, NJ
|publisher=[[Prentice Hall]]
|isbn=978-0-13-651589-0
}}</ref> between 150<ref name="Medlin1997">{{Cite book
|last1=Medlin
|first1=L. K.
|last2=Kooistra
|first2=Wiebe H. C. F.
|last3=Potter
|first3=Daniel
|last4=Saunders
|first4=Gary W.
|last5=Andersen
|first5=Robert A.
|title=Origins of Algae and their Plastids
|chapter=Phylogenetic relationships of the 'golden algae' (Haptophytes, heterokont chromophytes) and their plastids
|display-authors=1
|year=1997
|url=http://epic.awi.de/2100/1/Med1997c.pdf
|volume=11
|pages=187–219
|hdl=10013/epic.12690
|doi=10.1007/978-3-7091-6542-3_11
|series=Plant Systematics and Evolution
|isbn=978-3-211-83035-2
|access-date=27 August 2012
|archive-date=5 October 2013
|archive-url=https://web.archive.org/web/20131005084158/http://epic.awi.de/2100/1/Med1997c.pdf
|url-status=live
}}</ref> and 200 million years ago.<ref name="Lim1986">{{Cite journal
|last1=Lim
|first1=B.-L.
|last2=Kawai
|first2=H.
|last3=Hori
|first3=H.
|last4=Osawa
|first4=S.
|title=Molecular evolution of 5S ribosomal RNA from red and brown algae
|url=https://www.jstage.jst.go.jp/article/ggs1921/61/2/61_2_169/_pdf
|year=1986
|journal=[[Japanese Journal of Genetics]]
|volume=61
|issue=2
|pages=169–176
|doi=10.1266/jjg.61.169
|doi-access=free
|access-date=27 August 2012
|archive-date=10 January 2015
|archive-url=https://web.archive.org/web/20150110191502/https://www.jstage.jst.go.jp/article/ggs1921/61/2/61_2_169/_pdf
|url-status=live
}}</ref> In many ways, the evolution of the brown algae parallels that of the [[green algae]] and [[red algae]],<ref name="Dittmer1964" /> as all three groups possess complex multicellular species with an [[alternation of generations]]. Analysis of 5S [[Ribosomal RNA|rRNA]] sequences reveals much smaller evolutionary distances among genera of the brown algae than among genera of red or green algae,<ref name="Lim1986"/><ref>
{{cite journal
|last1=Hori |first1=H.
|last2=Osawa |first2=S.
|year=1987
|title=Origin and evolution of organisms as deduced from 5S ribosomal RNS sequences
|journal=[[Molecular Biology and Evolution]]
|volume=4 |issue=5 |pages=445–472
|pmid=2452957
|doi=10.1093/oxfordjournals.molbev.a040455
|doi-access=free
}}</ref> which suggests that the brown algae have diversified much more recently than the other two groups.

===Fossils===
The occurrence of Phaeophyceae as [[fossil]]s is rare due to their generally soft-bodied nature,<ref name="Arnold1947">
{{cite book
|last=Arnold |first=C. A.
|year=1947
|title=An Introduction to Paleobotany
|url=https://archive.org/details/in.ernet.dli.2015.50241 |page=[https://archive.org/details/in.ernet.dli.2015.50241/page/n64 48]
|location=New York; London
|publisher=[[McGraw-Hill]]
|isbn=978-1-4067-1861-4
}}</ref> and scientists continue to debate the identification of some finds.<ref>{{cite journal
|last1=Coyer
|first1=J. A.
|last2=Smith
|first2=G. J.
|last3=Andersen
|first3=R. A.
|year=2001
|title=Evolution of ''Macrocystis'' spp. (Phaeophyta) as determined by ITS1 and ITS2 sequences
|url=http://129.125.2.51/fmns-research/marbee/publications/CoyerJPhyc01.pdf
|journal=[[Journal of Phycology]]
|volume=37
|issue=4
|pages=574–585
|doi=10.1046/j.1529-8817.2001.037001574.x
|s2cid=84074495
|access-date=27 August 2012
|archive-date=16 October 2023
|archive-url=https://web.archive.org/web/20231016194154/https://www.rug.nl/research/fse/
|url-status=live
}}</ref> Part of the problem with identification lies in the [[convergent evolution]] of morphologies between many brown and red algae.<ref name="Fry1955">
{{cite journal
|last1=Fry |first1=W. L.
|last2=Banks |first2=H. P.
|year=1955
|title=Three new genera of algae from the Upper Devonian of New York
|journal=[[Journal of Paleontology]]
|volume=29 |issue=1
|pages=37–44
|jstor=1300127
}}</ref> Most fossils of soft-tissue algae preserve only a flattened outline, without the microscopic features that permit the major groups of multicellular algae to be reliably distinguished. Among the brown algae, only species of the genus ''[[Padina (alga)|Padina]]'' deposit significant quantities of minerals in or around their cell walls.<ref name="Prescott1968">
{{cite book
|last=Prescott |first=G. W.
|year=1968
|title=The Algae: A Review
|url=https://archive.org/details/algaereview0000pres |url-access=registration |pages=[https://archive.org/details/algaereview0000pres/page/207 207]–231, 371–372
|location=Boston
|publisher=[[Houghton Mifflin Company]]
|isbn=978-3-87429-244-3
}}</ref> Other algal groups, such as the [[red algae]] and [[green algae]], have a number of [[calcareous]] members. Because of this, they are more likely to leave evidence in the fossil record than the soft bodies of most brown algae and more often can be precisely classified.<ref name="Simpson1953">
{{cite book
|last=Simpson |first=G. G.
|year=1953
|title=Life of the Past: An Introduction to Paleontology
|url=https://archive.org/details/lifeofpastintr00simp |url-access=registration |pages=[https://archive.org/details/lifeofpastintr00simp/page/158 158–159]
|location=New Haven
|publisher=[[Yale University Press]]
}}</ref>

Fossils comparable in morphology to brown algae are known from strata as old as the Upper [[Ordovician]],<ref name="Fry1983">
{{cite journal
|last=Fry |first=W. L.
|year=1983
|title=An algal flora from the Upper Ordovician of the Lake Winnipeg region, Manitoba, Canada
|journal=[[Review of Palaeobotany and Palynology]]
|volume=39 |issue=3–4 |pages=313–341
|doi=10.1016/0034-6667(83)90018-0
|bibcode=1983RPaPa..39..313F
}}</ref> but the [[Taxonomy (biology)|taxonomic]] affinity of these impression fossils is far from certain.<ref>{{cite web
|last1=Speer
|first1=B. R.
|last2=Waggoner
|first2=B. M.
|year=2000
|title=Phaeophyta: Fossil Record
|url=http://www.ucmp.berkeley.edu/chromista/browns/phaeofr.html
|access-date=24 April 2007
|archive-date=9 June 2007
|archive-url=https://web.archive.org/web/20070609225826/http://www.ucmp.berkeley.edu/chromista/browns/phaeofr.html
|url-status=live
}}</ref> Claims that earlier [[Ediacaran]] fossils are brown algae<ref name="Loeblich1974">
{{Cite journal
|last=Loeblich |first=A. R.
|year=1974
|title=Protistan Phylogeny as Indicated by the Fossil Record
|journal=[[Taxon (journal)|Taxon]]
|volume=23 |issue=2/3 |pages=277–290
|doi=10.2307/1218707
|jstor=1218707 
}}</ref> have since been dismissed.<ref name=Lee2008/> While many [[carbon]]aceous fossils have been described from the [[Precambrian]], they are typically preserved as flattened outlines or fragments measuring only millimeters long.<ref name="Hofmann1985">
{{cite book
|last=Hofmann |first=H. J.
|year=1985
|chapter=Precambrian Carbonaceous Megafossils
|editor=D. F. Toomey |editor2=M. H. Nitecki
|title=Paleoalgology: Contemporary Research and Applications
|pages=20–33
|location=Berlin
|publisher=[[Springer-Verlag]]
}}</ref> Because these fossils lack features diagnostic for identification at even the highest level, they are assigned to fossil [[Form classification|form taxa]] according to their shape and other gross morphological features.<ref name="Hofmann1994">
{{cite book
|last=Hofmann |first=H. J.
|year=1994
|chapter=Proterozoic carbonaceous compressions ("metaphytes" and "worms")
|editor-last=Bengtson |editor-first=S.
|title=Life on Earth
|pages=342–357
|series=Nobel Symposium
|volume=84
|location=New York
|publisher=[[Columbia University Press]]
}}</ref> A number of [[Devonian]] fossils termed ''fucoids'', from their resemblance in outline to species in the genus ''[[Fucus]]'', have proven to be inorganic rather than true fossils.<ref name="Arnold1947"/> The Devonian megafossil ''[[Prototaxites]]'', which consists of masses of filaments grouped into trunk-like axes, has been considered a possible brown alga.<ref name="Bold1987">
{{cite book
|last1=Bold |first1=H. C.
|last2=Alexopoulos |first2=C. J.
|last3=Delevoryas |first3=T.
|year=1987
|title=Morphology of Plants and Fungi
|edition=5th |pages=112–131, 174–186
|location=New York
|publisher=[[Harper & Row Publishers]]
|isbn=978-0-06-040839-8
}}</ref> However, modern research favors reinterpretation of this fossil as a terrestrial [[fungus]] or fungal-like organism.<ref name="Hueber2001">
{{cite journal
|last1=Hueber |first1=F. M.
|year=2001
|title=Rotted wood-alga-fungus: the history and life of ''Prototaxites'' Dawson 1859
|journal=[[Review of Palaeobotany and Palynology]]
|volume=116 |issue=1 |pages=123–158
|doi=10.1016/S0034-6667(01)00058-6
|bibcode=2001RPaPa.116..123H
}}</ref> Likewise, the fossil ''[[Protosalvinia]]'' was once considered a possible brown alga, but is now thought to be an early [[land plant]].<ref name="Taylor 1987">
{{cite journal
 |last1        = Taylor
 |first1       = W. A.
 |last2       = Taylor
 |first2      = T. N.
 |year        = 1987
 |title       = Spore wall ultrastructure of ''Protosalvinia''
 |url         = http://paleobotany.bio.ku.edu/taylorPDFs%5C%5B1987%5D%20Taylor%20and%20Taylor-Spore%20wall%20ultrastructure%20of%20Protosalvinia.pdf
 |journal     = [[American Journal of Botany]]
 |volume      = 74
 |issue       = 3
 |pages       = 437–443
 |doi         = 10.2307/2443819
 |jstor       = 2443819
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20100617124912/http://paleobotany.bio.ku.edu/taylorPDFs/%5B1987%5D%20Taylor%20and%20Taylor-Spore%20wall%20ultrastructure%20of%20Protosalvinia.pdf
 |archive-date = 17 June 2010
}}</ref>

A number of [[Paleozoic]] fossils have been tentatively classified with the brown algae, although most have also been compared to known red algae species. ''[[Phascolophyllaphycus]]'' possesses numerous elongate, inflated blades attached to a stipe. It is the most abundant of algal fossils found in a collection made from [[Carboniferous]] strata in [[Illinois]].<ref name="Leary1986">
{{cite journal
|last=Leary |first=R. L.
|year=1986
|title=Three new genera of fossil noncalcareous algae from Valmeyeran (Mississippian) strata of Illinois
|journal=[[American Journal of Botany]]
|volume=73 |issue=3 |pages=369–375
|doi=10.2307/2444080
|jstor=2444080
}}</ref> Each hollow blade bears up to eight [[pneumatocyst]]s at its base, and the stipes appear to have been hollow and inflated as well. This combination of characteristics is similar to certain modern genera in the order [[Laminariales]] (kelps). Several fossils of ''[[Drydenia]]'' and a single specimen of ''[[Hungerfordia (alga)|Hungerfordia]]'' from the Upper Devonian of [[New York (state)|New York]] have also been compared to both brown and red algae.<ref name="Fry1955"/> Fossils of ''Drydenia'' consist of an elliptical blade attached to a branching filamentous holdfast, not unlike some species of ''[[Laminaria]]'', ''[[Porphyra]]'', or ''[[Gigartina]]''. The single known specimen of ''Hungerfordia'' branches dichotomously into lobes and resembles genera like ''[[Chondrus]]'' and ''[[Fucus]]''<ref name="Fry1955"/> or ''[[Dictyota]]''.<ref name="Bold1978">
{{cite book
|last1=Bold
|first1=H. C.
|last2=Wynne
|first2=M. J.
|year=1978
|title=Introduction to the Algae
|edition=2nd
|page=[https://archive.org/details/introductiontoal0000bold/page/27 27]
|publisher=[[Prentice-Hall]]
|isbn=978-0-13-477786-3
|url-access=registration
|url=https://archive.org/details/introductiontoal0000bold/page/27
}}</ref>

The earliest known fossils that can be assigned reliably to the Phaeophyceae come from [[Miocene]] [[diatomite]] deposits of the [[Monterey Formation]] in [[California]].<ref name="Hoek"/> Several soft-bodied brown macroalgae, such as ''[[Julescraneia]]'', have been found.<ref>
{{cite journal
|last1=Parker |first1=B. C.
|last2=Dawson |first2=E. Y.
|year=1965
|title=Non-calcareous marine algae from California Miocene deposits
|journal=[[Nova Hedwigia]]
|volume=10 |pages=273–295; plates 76–96
}}</ref>