{{Short description|Genus of algae}} {{Automatic taxobox | image = Tetrastrum heteracarthum EPA.jpg | image_caption = ''Tetrastrum heteracarthum'' | taxon = Tetrastrum | authority = R. Chodat, 1895 | type_species = ''Tetrastrum heteracanthum'' | type_species_authority = (Nordstedt) Chodat, 1895 | subdivision_ranks = Species | subdivision = * ''Tetrastrum asymmetricum'' * ''Tetrastrum constrictum'' * ''Tetrastrum elegans'' * ''Tetrastrum glabrum'' * ''Tetrastrum heteracanthum'' * ''Tetrastrum komarekii'' * ''Tetrastrum parallelum'' * ''Tetrastrum staurogeniaeforme'' * ''Tetrastrum tenuispinum'' * ''Tetrastrum triacanthum'' * ''Tetrastrum triangulare'' }} thumb|right|240px|''Tetrastrum glabrum''
'''''Tetrastrum''''' is a genus of green algae (Chlorophyta). It is a common component of the phytoplankton of freshwater habitats, particularly eutrophic and alkaline waters.<ref name=AlgaeBase/><ref name=Bicudo_and_Menezes2006>{{cite book | title= Gêneros de Algas de Águas Continentais do Brasil: chave para identificação e descrições | edition=2 | year=2006 | first1=Carlos E. M. |last1=Bicudo | first2=Mariângela | last2= Menezes | publisher= RiMa Editora | pages=508 | isbn= 857656064X }}</ref>
Although traditionally classified in the family Scenedesmaceae in the class Chlorophyceae, it is phylogenetically more closely related to the genus ''Oocystis'' of the family Oocystaceae (Trebouxiophyceae).<ref name=Bock/>
==History== The genus ''Tetrastrum'' has a tangled taxonomic history. The name was first coined in 1895 by Robert Chodat for the species ''Tetrastrum heteracanthum'', which was previously placed in the now-obsolete genus ''Staurogenia''. Later, the genus ''Cohniella'' was created by Ludwig Julius Bruno Schröder, containing the species ''Cohniella staurogeniiforme''. Later, Ernst Lemmermann merged the genus ''Cohniella'' into ''Tetrastrum''.<ref name=Bock/>
==Description== ''Tetrastrum'' consists of four-celled colonies, which are sometimes aggregated together to form compound colonies. A layer of mucilage surrounding the colony is sometimes present. Cells are tightly joined in a flat plane, with or without a small space in the middle. Cells are ovoid, triangular, or trapezoidal, 2–11.5 μm long. Some species may have spines on the cells; these spines are up to 46 μm and show various morphologies, such as one long spine and one short, or multiple short spines. Cells contain one nucleus and one to four chloroplasts, with or without pyrenoids. The cell wall appears smooth in light microscopy, but is covered with small granules which are visible in scanning electron microscopy.<ref name=AlgaeBase>{{AlgaeBase genus|id=43477|name=Tetrastrum|access-date=2023-12-06}}</ref>
''Tetrastrum'' reproduces asexually through the formation of autospores. Four autospores are formed, organized into the shape of the colony; these are released through a tear in the mother cell wall.<ref name=AlgaeBase/>
==Identification== ''Tetrastrum'' is similar to, and has been taxonomically confused with, other genera such as ''Crucigenia''. The main morphological difference between the two is the mode of reproduction. In ''Tetrastrum'', the daughter colonies are produced with the cells in the same orientation as the mother cells. In ''Crucigenia'', the daughter colonies are produced with cells rotated 45° relative to the mother cells' orientation. Additionally, ''Tetrastrum'' may produce spines on its cells, while ''Crucigenia'' never does.<ref name=Bock>{{cite journal | doi=10.1111/jpy.12039 | title=Classification of crucigenoid algae: Phylogenetic position of the reinstated genus ''Lemmermannia'', ''Tetrastrum'' spp. ''Crucigenia tetrapedia'', and ''C. lauterbornii'' (Trebouxiophyceae, Chlorophyta) | date=2013 | last1=Bock | first1=Christina | last2=Luo | first2=Wei | last3=Kusber | first3=Wolf-Henning | last4=Hegewald | first4=Eberhard | last5=Pažoutová | first5=Marie | last6=Krienitz | first6=Lothar | journal=Journal of Phycology | volume=49 | issue=2 | pages=329–339 | pmid=27008519 | bibcode=2013JPcgy..49..329B | s2cid=46206435 }}</ref> Some species once classified in the genus ''Tetrastrum'' have been reclassified into the genus ''Lemmermannia''. ''Lemmermannia'' has square colonies that lack spines, and can sometimes form compound colonies; in contrast, ''Tetrastrum'' has colonies with spines, or in the case of the spineless ''Tetrastrum glabrum'', has oval and not square colonies).<ref name=Bock/><ref>{{cite book | title= Chlorophyceae (Grünalgen), Ordnung Chlorococcales | last1=Komárek | first1=J. | last2=Fott | first2=B. | date=1983 | publisher= E. Schweizerbart'sche Verlagsbuchhandlung | series=Das Phytoplankton des Süßwassers | language=de| page=1044 }}</ref>
Species of ''Tetrastrum'' are identified based on the size and shape of the cells, placement and length of the spines, and presence or absence of pyrenoids.<ref name=AlgaeBase/> Considerable variation exists within species, blurring species boundaries.<ref>{{cite journal | doi=10.2307/2436189 | jstor=2436189 | title=The Algal Genus ''Tetrastrum'' | last1=Ahlstrom | first1=Elbert H. | last2=Tiffany | first2=Lewis H. | journal=American Journal of Botany | date=1934 | volume=21 | issue=8 | pages=499–507 }}</ref>
==References== {{Reflist}} * {{ITIS |id=6260 |taxon=''Tetrastrum'' |accessdate=19 September 2007}} * {{cite web | url = http://www.algaebase.org/search/genus/detail/?genus_id=43477&sk=0| title = ''Tetrastrum'' Genus detail | publisher = AlgaeBase | accessdate = 2007-09-19 | author = D. Garbary and E. Hegewald | date = 17 Aug 2004}}
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Category:Sphaeropleales genera Category:Sphaeropleales Category:Freshwater algae