Editing Algae (section)

{{Short description|Diverse group of photosynthetic organisms}}
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{{redirect|Alga}}
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{{Use dmy dates|date=October 2024}}
{{Infobox
| above            = Algae
| abovestyle       = background:{{taxobox colour|Viridiplantae}}
| subheader        = Organisms that perform oxygenic photosynthesis, except land plants
| image            = [[File:NSW seabed 1.JPG|210px]]
| caption          = Marine algae growing on the sea bed in shallow waters
| image2           = [[File:Водоросли пресноводного водоема 2.jpg|210px]]
| caption2         = Freshwater microscopic unicellular and colonial algae
| headerstyle      = background:{{taxobox colour|Viridiplantae}}
| labelstyle       = background:#dbffdb
| header1          = Algal divisions<ref name="Guiry-2024">{{cite journal |first1=Michael D. |last1=Guiry |author-link=Michael D. Guiry |title=How many species of algae are there? A reprise. Four kingdoms, 14 phyla, 63 classes and still growing |journal=Journal of Phycology |date=2024 |volume=60 |issue=2 |pages=214–228 |doi=10.1111/jpy.13431|pmid=38245909|doi-access=free }}</ref><ref>Guiry, M.D. & Guiry, G.M. 2025. ''[[AlgaeBase]]''. World-wide electronic publication, University of Galway. https://www.algaebase.org; searched on 25 May 2025.</ref>
| label2           = Prokaryotic
| data2            = [[Cyanobacteria]]
| label3           = Eukaryotic (primary endosymbiosis)
| data3            = [[Glaucophyta]], [[Rhodophyta]], [[Prasinodermophyta]], [[Chlorophyta]], [[Charophyta]]*
| label4           = Eukaryotic (secondary endosymbiosis)
| data4            = [[Chlorarachniophyta]], [[Chromerida]], [[Cryptophyta]], [[Dinoflagellata]], [[Euglenophyta]], [[Haptophyta]], [[Ochrophyta]]
| data5            = <nowiki>*</nowiki>[[Paraphyly|paraphyletic]], it excludes land plants
| header6          = [[#Diversity|Diversity]]
| label7           = Living
| data7            = 50,605 species
| label8           = Fossil
| data8            = 10,556 species
}}

'''Algae''' ({{IPAc-en|UK|ˈ|æ|l|ɡ|i:}} {{respell|AL|ghee}}, {{IPAc-en|US|ˈ|æ|l|dʒ|i:|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-algae.wav}} {{respell|AL|jee}};<ref>{{Cite web |url=https://dictionary.cambridge.org/dictionary/english/algae |title=ALGAE &#124; English meaning - Cambridge Dictionary |access-date=6 April 2023}}</ref> {{Singular}}: '''alga''' {{IPAc-en|ˈ|æ|l|ɡ|ə|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-alga.wav}} {{respell|AL|gə}}) is an informal term for any [[organism]]s of a large and diverse group of [[photosynthesis|photosynthetic]] organisms that are not [[Plant|plants]], and includes [[species]] from multiple distinct [[clade]]s. Such organisms range from [[unicellular]] [[microalgae]], such as [[cyanobacteria]],{{efn|Some botanists restrict the name ''[[algae]]'' to eukaryotes, which does not extend to cyanobacteria, which are [[prokaryote]]s.{{citation needed|reason=This contradicts the position of the [[ICNafp]], so is not true for all botanists. |date=May 2025}}}} ''[[Chlorella]]'', and [[diatom]]s, to [[multicellular]] [[macroalgae]] such as kelp or [[brown algae]] which may grow up to {{convert|50|m}} in length. Most algae are aquatic organisms and lack many of the distinct cell and tissue types, such as [[stoma]]ta, [[xylem]], and [[phloem]] that are found in [[embryophyte|land plants]]. The largest and most complex marine algae are called [[seaweed]]s. In contrast, the most complex freshwater forms are the [[Charophyta]], a [[Division (taxonomy)|division]] of [[green algae]] which includes, for example, ''[[Spirogyra]]'' and [[stonewort]]s. Algae that are carried passively by water are [[plankton]], specifically [[phytoplankton]].

Algae constitute a [[Polyphyly|polyphyletic]] group<ref name="Nabors-2004" /> because they do not include a [[common ancestor]], and although [[Eukaryote|eukaryotic]] algae with [[chlorophyll]]-bearing [[plastid]]s seem to have a single origin (from [[symbiogenesis]] with [[cyanobacteria]]),<ref name="Keeling-2004">{{cite journal |title=Diversity and evolutionary history of plastids and their hosts |first=Patrick J. |last=Keeling |journal=American Journal of Botany |year=2004 |volume=91 |pages=1481–1493 |doi=10.3732/ajb.91.10.1481 |issue=10 |pmid=21652304 |doi-access=free |bibcode=2004AmJB...91.1481K }}</ref> they were acquired in different ways. Green algae are a prominent example of algae that have primary [[chloroplast]]s derived from [[endosymbiont]] cyanobacteria. [[Diatom]]s and brown algae are examples of algae with secondary chloroplasts derived from endosymbiotic [[red algae]], which they acquired via [[phagocytosis]].<ref>{{cite journal |first1=J. D. |last1=Palmer |first2=D. E. |last2=Soltis |first3=M. W. |last3=Chase |year=2004 |title=The plant tree of life: an overview and some points of view |journal=American Journal of Botany |volume=91 |issue=10 |pages=1437–1445 |doi=10.3732/ajb.91.10.1437 |pmid=21652302 |doi-access=free}}</ref> Algae exhibit a wide range of reproductive strategies, from simple [[asexual reproduction|asexual]] cell division to complex forms of [[sexual reproduction]] via [[spore]]s.<ref>Smithsonian National Museum of Natural History; Department of Botany. {{cite web |url=http://botany.si.edu/projects/algae/introduction.htm |title=Algae Research |access-date=25 August 2010 |url-status=live |archive-url=https://web.archive.org/web/20100702180840/http://botany.si.edu/projects/algae/introduction.htm |archive-date=2 July 2010}}</ref>

Algae lack the various structures that characterize [[plant]]s (which evolved from freshwater green algae), such as the phyllids (leaf-like structures) and [[rhizoid]]s of [[bryophyte]]s ([[non-vascular plant]]s), and the [[root]]s, [[leaf|leaves]] and other [[xylem]]ic/[[phloem]]ic [[organ (biology)|organ]]s found in [[tracheophyte]]s ([[vascular plant]]s). Most algae are [[autotroph]]ic, although some are [[mixotroph]]ic, deriving energy both from photosynthesis and uptake of organic carbon either by [[osmotrophy]], [[Myzocytosis|myzotrophy]] or [[phagocytosis|phagotrophy]]. Some unicellular species of green algae, many [[golden algae]], [[euglenid]]s, [[dinoflagellate]]s, and other algae have become [[heterotroph]]s (also called colorless or apochlorotic algae), sometimes [[parasitic]], relying entirely on external energy sources and have limited or no photosynthetic apparatus.<ref>Pringsheim, E. G. 1963. ''Farblose Algen. Ein beitrag zur Evolutionsforschung''. Gustav Fischer Verlag, Stuttgart. 471 pp., [[species:Algae#Pringsheim (1963)]].</ref><ref>{{cite journal |last1=Tartar |first1=A. |last2=Boucias |first2=D. G. |last3=Becnel |first3=J. J. |last4=Adams |first4=B. J. |year=2003 |title=Comparison of plastid 16S rRNA (rrn 16) genes from Helicosporidium spp.: Evidence supporting the reclassification of Helicosporidia as green algae (Chlorophyta) |journal=International Journal of Systematic and Evolutionary Microbiology |volume=53 |pages=1719–1723 |doi=10.1099/ijs.0.02559-0 |pmid=14657099 |issue=Pt 6 |doi-access=free}}</ref><ref>{{cite journal |last1=Figueroa-Martinez |first1=F. |last2=Nedelcu |first2=A. M. |last3=Smith |first3=D. R. |last4=Reyes-Prieto |first4=A. |year=2015 |title=When the lights go out: the evolutionary fate of free-living colorless green algae |journal=New Phytologist |volume=206 |issue=3 |pages=972–982 |doi=10.1111/nph.13279 |pmid=26042246 |pmc=5024002|bibcode=2015NewPh.206..972F }}</ref> Some other heterotrophic organisms, such as the [[apicomplexans]], are also derived from cells whose ancestors possessed chlorophyllic plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery ultimately derived from cyanobacteria that produce [[oxygen]] as a [[byproduct]] of splitting [[water molecule]]s, unlike other organisms that conduct [[anoxygenic photosynthesis]] such as [[purple sulfur bacteria|purple]] and [[green sulfur bacteria]]. Fossilized filamentous algae from the [[Vindhya]] basin have been dated to 1.6 to 1.7&nbsp;billion years ago.<ref>{{cite journal |pmid=19416859 |year=2009 |last1=Bengtson |first1=S. |last2=Belivanova |first2=V. |last3=Rasmussen |first3=B. |last4=Whitehouse |first4=M. |title=The controversial 'Cambrian' fossils of the Vindhyan are real but more than a billion years older |volume=106 |issue=19 |pages=7729–7734 |doi=10.1073/pnas.0812460106 |pmc=2683128 |journal=Proceedings of the National Academy of Sciences of the United States of America |bibcode=2009PNAS..106.7729B |doi-access=free }}</ref>

Because of the wide range of types of algae, there is a correspondingly wide range of industrial and traditional applications in human society. Traditional [[seaweed farming]] practices have existed for thousands of years and have strong traditions in [[East Asia]]n food cultures. More modern [[algaculture]] applications extend the [[Edible seaweed|food traditions]] for other applications, including cattle feed, using algae for [[bioremediation]] or pollution control, transforming sunlight into [[algae fuel]]s or other chemicals used in industrial processes, and in medical and scientific applications. A 2020 review found that these applications of algae could play an important role in [[carbon sequestration]] to [[Climate change mitigation|mitigate climate change]] while providing lucrative value-added products for global economies.<ref>{{Cite book |last1=Paul |first1=Vishal |last2=Chandra Shekharaiah |first2=P. S. |last3=Kushwaha |first3=Shivbachan |last4=Sapre |first4=Ajit |last5=Dasgupta |first5=Santanu |last6=Sanyal |first6=Debanjan |title=Renewable Energy and Climate Change |chapter=Role of Algae in CO2 Sequestration Addressing Climate Change: A Review |date=2020 |editor-last=Deb |editor-first=Dipankar |editor2-last=Dixit |editor2-first=Ambesh |editor3-last=Chandra |editor3-first=Laltu |chapter-url=https://link.springer.com/chapter/10.1007/978-981-32-9578-0_23 |series=Smart Innovation, Systems and Technologies |volume=161 |language=en |location=Singapore |publisher=Springer |pages=257–265 |doi=10.1007/978-981-32-9578-0_23 |isbn=978-981-329-578-0 |s2cid=202902934}}</ref>