Green algae

Green algae

Paraphyletic group
name = Green algae



regnum = Plantae
includes =
*Chlorophyta
*Charophyta
excludes = *Embryophyta

The green algae (singular: green alga) are the large group of algae from which the embryophytes (higher plants) emerged.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] 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 flagellates, usually but not always with two 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. Thomas, D. 2002. "Seaweeds." The Natural History Museum, London. ISBN 0 565 09175 1] Many species live most of their lives as single cells, while other species form colonies or long filaments.

A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in euglenids and chlorarachniophytes were acquired from ingested green algae, 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 lichens. 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 chlorophylls "a" and "b", giving them a bright green colour (as well as the accessory pigments beta carotene and xanthophylls),Burrows 1991. "Seaweeds of the British Isles." Volume 2 Natural History Museum, London. ISBN 0 565 00981 8] and have stacked thylakoids.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]

All green algae have mitochondria with flat cristae. When present, flagella are typically anchored by a cross-shaped system of microtubules, 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 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. [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 ]

* Chlorophyta
** Chlorophyceae
** Ulvophyceae
** Trebouxiophyceae
* Chlorokybales
* Klebsormidiales
* Zygnematales
* Desmidiales
* 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. [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]

Reproduction

Green algae are eukaryotic organisms that follow a reproduction cycle called alternation of generations.

Reproduction varies from fusion of identical cells (isogamy) to 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 prasinophytes.

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]

Chemistry

The green algae span a wide range of d13c values, with different groups having different typical ranges.

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]

ee also

*Algae
*Brown algae
*Chlorophyll
*"Codium"
*Plants
*Prasiola
*Red algae
*Sea lettuce
*Seaweed


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • green algae — pl.n. any of a division (Chlorophycota) of photosynthetic thallophytes in which the chlorophyll is not obscured by other pigments: a type of ALGAE …   English World dictionary

  • green algae — green′ al′gae n. pl. mcr grass green algae of the phylum Chlorophyta, common on wet rocks, damp wood, and the surface of stagnant water …   From formal English to slang

  • green algae — any grass green, chiefly freshwater algae of the phylum Chlorophyta, often growing on wet rocks, damp wood, or on the surface of stagnant water. [1900 05] * * * ▪ algae division       members of the division Chlorophyta, comprising between 9,000… …   Universalium

  • green algae — žaliadumbliai statusas T sritis ekologija ir aplinkotyra apibrėžtis Eukariotų (Eukaryota) domeno pirmuonių (Protista) karalystės skyriaus dumbliai (Chlorophyta). Išsiskiria žalia spalva, kurią lemia chlorofilas, kaupiamas chromatoforuose. Nuo… …   Ekologijos terminų aiškinamasis žodynas

  • green algae — noun algae that are clear green in color; often growing on wet ricks or damp wood or the surface of stagnant water (Freq. 1) • Syn: ↑chlorophyte • Hypernyms: ↑alga, ↑algae • Hyponyms: ↑sea lettuce, ↑ …   Useful english dictionary

  • green algae — /grin ˈældʒi/ (say green aljee) noun algae belonging to the division Chlorophyta, grass green in colour …  

  • green algae — plural noun algae which contain chlorophyll and store starch in discrete chloroplasts. [Division Chlorophyta.] …   English new terms dictionary

  • Green algae — See Chlorophyta …   Dictionary of molecular biology

  • green algae — noun The chlorophytes …   Wiktionary

  • blue-green algae — Biol. a widely distributed group of predominantly photosynthetic prokaryotic organisms of the subkingdom Cyanophyta, resembling phototrophic bacteria, occurring singly or in colonies in diverse habitats: some species can fix atmospheric nitrogen …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”