Cosmarium Corda ex Ralfs   

Kingdom: Plantae
Phylum: Chlorophyta – green algae
Class: Zygnematophyceae
Order: Desmidiales

British distribution (genus): Widespread, freshwater.
World distribution (genus): Throughout most of the world.

A very large genus of typical placoderm desmids, with the cells deeply constricted to form two semicells. Each semicell contains a single, large chloroplast with two pyrenoids. The cells are slowly motile by mucilage secretion and there are signs of this mucilage visible in the photograph (in the medium surrounding the cells, and enhanced by the Nomarski differential interference contrast used when taking the photograph).

Freshwater, usually in oligotrophic, acid waters, but not always so.

Photographs of material ex culture, 1998, species unnamed but likely to be C. botrytis

© A.J. Silverside
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