Home / Charophyceae / Desmids / Unicells/ Placoderm / Cosmarium
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Name derivation:
Ornament place, more liberally: Ornamented cell cosm (Gr.) = ornament, -arium = place
Classification:
Cosmarium Corda ex Ralfs 1848; 1,050 of 2,294 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013). Order Desmidiales; Family Desmidiaceae
Morphology:
Single-celled placoderm. The cells are deeply divided in the middle which holds the nucleus. The two semicells are rounded when views from the front and flattened, oval, or elliptic when viewed from the side. The older half of the cell wall secretes mucilage. The mucilage swells as it absorbs water and propels the cell forward. The cell wall may be smooth with pores or ornamented with granules, pits, or warts. The vegetative cells usually do not have spines. Each semicell has at least one central chloroplast. They sometimes produces thick-walled resting cells. Asexual reproduction by cell division.
Molecular sequences:
Cosmarium is highly polyphyletic based on nuclear SSU rDNA (Gontcharov and Melkonian 2005).
Similar genera:
Disphinctium connatum and D. cucurbita appear to be synonyms with Cosmarium connatum and C. cucurbita respectively (Croasdale 1956).
Habitat:
Mainly in acidic, oligotrophic, aquatic environments. Occasionally subaerial or in basic, eutrophic waters.
References:
Croasdale, H. 1956. Freshwater algae of Alaska. I. Some desmids from the Interior. Part 2: Actinotaenium, Micrasterias and Cosmarium. Transactions of the American Microscopical Society LXXV(1):1-70). Gontcharov, A.A., and M. Melkonian 2003. Molecular phylogeny of Staurastrum Meyen ex Ralfs and related genera (Zygnematophyceae, Streptophyta) based on coding and noncoding rNA sequence comparisons. Journal of Phycology 41:887-899. Guiry, M.D. and G.M. Guiry 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 29 January 2013. Ralfs, J. (1848). The British Desmidieae. pp. [i]-xxii, [i], [1]-226, pls I-XXXV. London: Reeve, Benham & Reeve.