Two cells of Cosmarium obliquum in a characteristic, somewhat oblique, frontal view.

Cell dimensions (L x B): 20 x 18 µm


Desmid of the month
June 2008

Cosmarium obliquum

C. obliquum is a remarkable Cosmarium in that its cells show only two planes of symmetry (instead of three). In apical view, cells are not elliptical but about semicircular. Because of this peculiar characteristic this species sometimes is placed in a separate genus*. After division, cells of C. obliquum often stick together for some time so that short chains (2 to 4 cells) may be encountered. In Europe C. obliquum is widely distributed but mainly in mountainous regions. Only in 2007 it was found for the first time in the Netherlands, on some acidic, oligotrophic moorland sites in the province of Drenthe.

* genus Nothocosmarium, established by Raciborski, in 1889.

Image © Marien van Westen

Cell of C. obliquum in apical view: strongly convex (about semicircular) on one side, almost straight on the other side.

Image © Marien van Westen

Cell of C. obliquum in oblique apical view, clearly showing its little-symmetric morphology.

Image © Marien van Westen

A four-cell chain of C. obliquum (in straight frontal view)

SEM picture of a cell of C. obliquum showing distinct pore fields.