Cosmarium benedictum
image © Alfred van Geest

Cosmarium benedictum. Notice flattened, marginal crenations and shallow, opened sinus. Cell dimensions (L x B): 44 x 26 µm.



Cosmarium benedictum
image © Alfred van Geest

SEM picture of C. benedictum in frontal view. Notice slight traces of a transversal, supraisthmial band of granules only being present in the lower semicell.



 


Desmid of the Month
May 2026

Cosmarium benedictum


Cosmarium benedictum belongs to a group of granulate-crenulate Cosmaria the cells of which are characterized by a relatively broad isthmus and a transversal supraisthmial band of longitudinal series of granules. However, in C. benedictum those series of supraisthmial granules are but very weakly developed or even completely absent. As compared to the somewhat similar C. notabile (desmid of April 2026) marginal crenations in C. benedictum are much more flattened. Moreover, the cell sinus is shallower and opened from a U-shaped apex. Zygospores are globose and furnished with short, blunt spines arising from a conical base. In the Netherlands, C. benedictum is a rare species, only known from some ephemeral puddles at Amsterdam.

Cosmarium benedictum
image © Alfred van Geest

SEM picture of Cosmarium benedictum in lateral view.

Cosmarium benedictum
image © Alfred van Geest

Zygospore of Cosmarium benedictum