Cosmarium tetragonum

Cosmarium tetragonum
Scientific classification
Clade:	Viridiplantae
(unranked):	Charophyta
Class:	Zygnematophyceae
Order:	Desmidiales
Family:	Desmidiaceae
Genus:	Cosmarium
Species:	C. tetragonum
Binomial name
	Cosmarium tetragonum; (Nägeli) W.Archer in Pritchard 1861
Varieties
	Cosmarium tetragonum var. elegans (Roy & Bisset) West & G.S.West 1908 (syn. C. elegans)
Synonyms
	Euastrum tetragonum Nägeli

Cosmarium tetragonum is a species of green algae in the family Desmidiaceae. It is a freshwater species with a worldwide distribution.

Description

The nominate variety (var. tetragonum) is about 35 to 48 μm long, and 20 to 26 μm wide, 14 to 18 μm thick, with an isthmus about 6 to 12 μm long. Semicells are roughly rectangular in outline, with undulate margins; each side has about four bumps and the top side has about two bumps.^[3]

Varieties

Cosmarium tetragonum is variable and several varieties have been described. They are:

Variety lundelii differs from the nominate variety that the lateral bumps are unequal; the two median bumps are larger.^[3]
Variety bipapillatum also has two median bumps that are larger, but also has a protuberance right at the base of the semicell, near the isthmus.^[3]
Variety ornatum has a crease that follows the margin of the cell; the crease may also have projections near the apex of the semicell.^[3]
Variety intermedium has stout cells that are 1.5 times as long as broad; semicells are more trapezoidal.^[3]

References

^ Pritchard, A. (1861). A history of infusoria, including the Desmidiaceae and Diatomaceae, British and foreign. Fourth edition enlarged and revised by J. T. Arlidge, M.B., B.A. Lond.; W. Archer, Esq.; J. Ralfs, M.R.C.S.L. ; W. C. Williamson, Esq., F.R.S., and the author. pp. i-xii, 1- 968, 40 pls. London: Whittaker and Co., Ave Maria Lane. (description page 732)
^ West, W. & West, G.S. (1908). A monograph of the British Desmidiaceae. III. pp. [i]-xv, [1]-274, pl. 65-95. London: The Ray Society. (description page 20)
^ ^a ^b ^c ^d ^e Prescott, G. W.; Croasdale, H. T.; Vinyard, W. C.; Bicudo, C. E. M. (1981). A Synopsis of North American Desmids. Part II: Desmidiaceae: Placodermae. Section 3. Lincoln: University of Nebraska Press. p. 720. ISBN 9780835737920.

External links

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[1] Pritchard, A. (1861). A history of infusoria, including the Desmidiaceae and Diatomaceae, British and foreign. Fourth edition enlarged and revised by J. T. Arlidge, M.B., B.A. Lond.; W. Archer, Esq.; J. Ralfs, M.R.C.S.L. ; W. C. Williamson, Esq., F.R.S., and the author. pp. i-xii, 1- 968, 40 pls. London: Whittaker and Co., Ave Maria Lane. (description page 732)

[2] West, W. & West, G.S. (1908). A monograph of the British Desmidiaceae. III. pp. [i]-xv, [1]-274, pl. 65-95. London: The Ray Society. (description page 20)

[Prescott1981-3] Prescott, G. W.; Croasdale, H. T.; Vinyard, W. C.; Bicudo, C. E. M. (1981). A Synopsis of North American Desmids. Part II: Desmidiaceae: Placodermae. Section 3. Lincoln: University of Nebraska Press. p. 720. ISBN 9780835737920.

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