Cosmarium ornatum. Notice about reniform semicells with produced, truncate apex.

Cell dimensions (L x B): ca 35 x 35 µm

Empty cell of C. ornatum showing cell wall sculpturing. Notice concentric series of granules in the semicell centre separated from intramarginal granules by a broad unsculptured zone.



Desmid of the month
March 2021

Cosmarium ornatum

C. ornatum is a medium-sized, granulate Cosmarium species.  Cells are about as long as broad and semicells are a bit reniform with a slightly produced, broadly truncate apex. Centre of the semicell is distinctly inflated and ornamented with concentric series of granules. This central sculpture is separated from series of intramarginal granules by an unsculptured zone.
In the Netherlands, C. ornatum is of occasional occurrence in acidic, meso-oligotrophic moorland pools.

Another cell of C. ornatum in frontal view. Each semicell with a couple of pyrenoids.

Iimage © Alfred van Geest

Cell of C. ornatum in apical view. Notice central inflation of semicell.

Image © Jan Šťastný 

SEM image of C. ornatum