Desmid of the month
April 2008

Cosmarium subgranatum

Cosmarium subgranatum belongs to a group of small-sized Cosmaria marked by a smooth cell wall with (in frontal view) an undulate margin. Semicells are about pyramidal in outline and undulations of the margin are pretty irregular. In the Netherlands (like in many other countries) C. subgranatum is a common species in meso-eutrophic water bodies, both acidic and alkaline. Its var. borgei differing from the nominate variety by  broader, more flattened cell apices seems to be more tolerant to eutrophic conditions than the nominate variety (var. subgranatum).

Cosmarium subgranatum (var. borgei). Notice the pyramidal, irregularly undulate outline of the semicells.

Cell dimensions (L x B): 25  x 20 µm


Cells of Cosmarium subgranatum (var. borgei) within a nodule of the blue-green alga Gloeotrichia pisum


Scanning electron microscope (SEM) picture of a C. subgranatum cell. Note that the cell wall at this high magnification appears to be not perfectly smooth. Among the shallow pits also scattered pores can be noticed

(click for larger image).

Scale bar = 10 µm

Image: Hanny Kooijman-van Blokland © IBED