Light microscopical photo of Cosmarium pseudoinsigne focussed on the row of pronounced, subapical cell wall tubercles. Note also hexagonals of cell wall pits (bright dots) in the centre of the semicells.

size (L x B): ca. 50x40 µm



Desmid of the month
April 2003

Cosmarium pseudoinsigne

At a low microscopic magnification Cosmarium pseudoinsigne* does not look particularly spectacular, resembling many other Cosmarium species with a granulated cell wall. However, at higher magnification and optimal focussing a row of prominent tubercles is to be seen, just below the apex. Under optimal conditions of observation, e.g. in  dead, empty cells, it appears that also the rest of the cell wall is provided with elevations, albeit that those are must more flattened than the subapical ones. Each swelling is surrounded by a hexagon of marked pits (scrobiculae) in each of which a cell wall pore is located (image on the right).

In Europe, the main point of distribution of C. pseudoinsigne is in the western part of the continent, where slightly alkaline, mesotrophic lowland pools form its appropriate habitat.

SEM image
image © Eberhard Hegewald

SEM photo  showing hexagons of cell wall pits, each of them housing the outlet of a cell wall pore. The short threads attached near the scrobiculae (especially in the older semicell) might be bacteria feeding on excretion products released by the cell wall pores.

* The species under discussion is better known under the name of Cosmarium insigne, a name, however that appeared to be an invalid homonym, see Prescott et al. (1981).


Prescott, G.W., H.T. Croasdale, W.C. Vinyard & C.E.M. Bicudo. 1981. A Synopsis of North American Desmids. Part 2, Section 3. University of Nebraska Press, Lincoln/London.

detail of scrobiculae with cell pores