Green algae
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222285868
2008-06-28T14:45:50Z
Kingdon
668610
No objection to Paraphyletic group template, I suppose, but let's fix some errors in how it was being invoked
{{Paraphyletic group
| name = Green algae
| image = Green algae.jpg
| regnum = [[Plantae]]
| includes =
*[[Chlorophyta]]
*[[Charophyta]]
| excludes = *[[Embryophyta]]
}}
The '''green algae''' (singular: '''green alga''') are the large group of [[alga]]e from which the [[embryophyte]]s (higher plants) emerged.<ref name="palmer">{{cite journal | url = http://www.amjbot.org/cgi/content/full/91/10/1437 | title = The plant tree of life: an overview and some points of view | author = Jeffrey D. Palmer, Douglas E. Soltis and Mark W. Chase | journal = American Journal of Botany | year = 2004 | volume = 91 | pages = 1437–1445 | doi = 10.3732/ajb.91.10.1437}}</ref> As such, they form a [[paraphyletic]] group, although the group including both green algae and embryophytes is monophyletic (and often just known as kingdom [[Plantae]]). The green algae include unicellular and colonial [[flagellate]]s, usually but not always with two [[flagellum|flagella]] per cell, as well as various colonial, coccoid, and filamentous forms. In the [[Charales]], the closest relatives of higher plants, full differentiation of tissues occurs. There are about 6000 species of green algae. <ref name="Thomas 02">Thomas, D. 2002. ''Seaweeds.'' The Natural History Museum, London. ISBN 0 565 09175 1</ref> Many species live most of their lives as single-cells, other species form colonies or long filaments.
A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in [[euglenid]]s and [[chlorarachniophyte]]s were acquired from ingested green algae,<ref name="palmer" /> and in the latter retain a vestigial nucleus (nucleomorph). Some species of green algae, particularly of genera ''[[Trebouxia]]'' or ''[[Pseudotrebouxia]]'' (Trebouxiophyceae), can be found in symbiotic associations with [[fungi]] to form [[lichen]]s. In general the fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus.
==Cellular structure==
Almost all forms have chloroplasts. These contain [[chlorophyll]]s ''a'' and ''b'', giving them a bright green colour (as well as the accessory pigments [[beta carotene]] and [[xanthophyll]]s),<ref name="Burrows 91">Burrows 1991. ''Seaweeds of the British Isles.'' Volume '''2''' Natural History Museum, London. ISBN 0 565 00981 8</ref> and have stacked [[thylakoid]]s.<ref name="Hoek 95">Hoek, C. van den, Mann, D.G. and Jahns, H.M. 1995. ''[http://books.google.co.uk/books?id=xuUoiFesSHMC&printsec=frontcover Algae An introduction to phycology]''. Cambridge University Press, Cambridge. ISBN 0 521 30419 9</ref>
All green algae have [[mitochondrion|mitochondria]] with flat cristae. When present, [[flagellum|flagella]] are typically anchored by a cross-shaped system of [[microtubule]]s, but these are absent among the higher plants and charophytes. Flagella are used to move the organism. Green algae usually have cell walls containing [[cellulose]], and undergo open [[mitosis]] without [[centrioles]].
==Origins==
The chloroplasts of green algae are bound by a double membrane, so presumably they were acquired by direct [[endosymbiotic theory|endosymbiosis]] of [[cyanobacteria]]. A number of cyanobacteria show similar pigmentation, but this appears to have arisen more than once, and the chloroplasts of green algae are no longer considered closely related to such forms. Instead, the green algae probably share a common origin with the [[red algae]].
==Classification==
Green algae are often classified with their embryophyte descendants in the green plant [[clade]] [[Viridiplantae]] (or [[Chlorobionta]]). Viridiplantae, together with red algae and [[glaucophyte]] algae, form the supergroup [[Primoplantae]], also known as [[Archaeplastida]] or Plantae ''sensu lato''.
Classification systems which have a kingdom of [[Protista]] may include green algae in the Protista or in the Plantae.<ref>{{cite journal | url = http://www.pubmedcentral.nih.gov/pagerender.fcgi?tool=pmcentrez&artid=372943&pageindex=1 | title = Kingdom protozoa and its 18 phyla | author = T Cavalier-Smith | journal = Microbiol Rev. | date = 1993 December | volume = 57 | issue = 4 | pages = 953–994 | id = [[PubMed Central]] PMC372943 | pmid = 8302218 }}</ref>
[[Image:Intertidal greenalgae.jpg|280px|thumb|right|A growth of the green seaweed, ''[[Enteromorpha]]'' on rock substratum at the ocean shore. Some green seaweeds, such as ''Enteromorpha'' and ''[[Sea lettuce|Ulva]]'', are quick to utilize inorganic [[nutrient]]s from land runoff, and thus can be indicators of nutrient pollution.]]
* [[Chlorophyta]]
** [[Chlorophyceae]]
** [[Ulvophyceae]]
** [[Trebouxiophyceae]]
* [[Chlorokybales]]
* [[Klebsormidiales]]
* [[Zygnematales]]
* [[Desmid]]iales
* [[Coleochaetales]]
* [[Charales]] (stoneworts)
The orders outside the Chlorophyta are often grouped as the division [[Charophyta]], which is [[paraphyletic]] to higher plants, together comprising the [[Streptophyta]]. Sometimes the Charophyta is restricted to the Charales, and a division Gamophyta is introduced for the Zygnematales and Desmidiales. In older systems the Chlorophyta may be taken to include all the green algae, but taken as above they appear to form a monophyletic group.
One of the most basal green algae is the [[flagellate]] ''[[Mesostigma]]'', although it is not yet clear whether it is sister to all other green algae, or whether it is one of the more basal members of the [[Streptophyta]].<ref name="palmer" /><ref>{{cite journal | url = http://www.biomedcentral.com/1471-2229/6/2 | title = EST analysis of the scaly green flagellate Mesostigma viride (Streptophyta): Implications for the evolution of green plants (Viridiplantae) | author = Andreas Simon, Gernot Glöckner, Marius Felder, Michael Melkonian and Burkhard Becker | journal = BMC Plant Biology | year = 2006 | volume = 6 | issue = 2 | doi = 10.1186/1471-2229-6-2 | pages = 2}}</ref>
[[Image:Algaeconjugate.jpg|thumb|right|Green Algae conjugating]]
==Reproduction==
Green algae are eukaryotic organisms that follow a reproduction cycle called [[alternation of generations]].
Reproduction varies from fusion of identical cells (isogamy) to [[fertilisation|fertilization]] of a large non-motile cell by a smaller motile one (oogamy). However, these traits show some variation, most notably among the basal green algae, called [[prasinophyte]]s.
Haploid algae cells (containing only one copy of their DNA) can fuse with other haploid cells to form diploid zygotes. When filamentous algae do this, they form bridges between cells, and leave empty cell walls behind that can be easily distinguished under the light microscope. This process is called ''conjugation''.
The species of ''Ulva'' are reproductively isomorphic, the [[diploid]] vegetative phase is the site of [[meiosis]] and releases haploid zoospores, which germinate and grow producing a haploid phase alternating with the vegetative phase. [http://www.mbari.org/staff/conn/botany/greens/anna/frontpages/lifecyc.htm]
== References ==
<references/>
*{{cite journal |quotes=no |author=Lewis, L. A & R. M. McCourt |year=2004 |title=Green algae and the origin of land plants|
*journal=[[American Journal of Botany]] |volume=91 |issue=10 |pages=1535–1556 |url=http://www.amjbot.org/cgi/reprint/91/10/1535?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&searchid=1&FIRSTINDEX=0&sortspec=relevance&volume=91&firstpage=1535&resourcetype=HWCIT}}
*[http://home.arcor.de/stefan.wic/diplomarbeit.pdf#search=%22%22stefan%20wic%22%22/ Green algae and cyanobacteria in lichens]
*[http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html Green algae (UC Berkeley)]
*[http://www.mbari.org/staff/conn/botany/flora/green.htm Monterey Bay green algae]
==See also==
*[[Algae]]
*[[Brown algae]]
*[[Chlorophyll]]
*''[[Codium]]''
*[[Plant]]s
*[[Prasiola]]
*[[Red algae]]
*[[Sea lettuce]]
*[[Seaweed]]
[[Category:Green algae]]
[[Category:Non-vascular plants]]
[[bg:Зелени водорасли]]
[[de:Grünalgen]]
[[eo:Verda algo]]
[[et:Rohevetikad]]
[[es:Chlorophyta]]
[[fr:Algue verte]]
[[hr:Zelena alga]]
[[hu:Zöldmoszatok]]
[[id:Ganggang hijau]]
[[lb:Gréngalgen]]
[[mk:Зелени алги]]
[[ja:緑藻類]]
[[pl:Zielenice]]
[[tr:yeşil algler]]
[[fi:Viherlevät]]
[[sl:Zelene alge]]
[[sv:Grönalger]]
[[uk:Водорості (підцарство)]]
[[zh:綠藻]]