Cosmarium granatum. Notice pyramidate outline of the semicells and truncate apices. Notice in this cell also an abrupt transition at the lateral sides between the slightly divergent basal parts and the strongly converging polar parts.

Cell dimensions (L x B): 30 x 20 µm



Desmid of the month
December 2020

Cosmarium granatum

C. granatum is a rather small to moderately large-sized species belonging to the group of smooth-walled Cosmaria. Its main characteristic is the outline of the semicells, viz. pyramidate with a truncate apex. Usually, the lateral sides are subparallel or even slightly divergent at their base, then they abruptly converge towards the apex. However, a more gradual converging from base to apex may be noticed as well.  Zygospores are globose and furnished with a number of short, blunt spines arising from a pyramidate base. In the Netherlands, C. granatum is a rather common species in various slightly acidic to slightly alkaline water bodies. Zygospores were encountered but a few times.

Another cell of C. granatum with a more gradual transition between basal and polar part of the semicell.

SEM picture of C. granatum. Notice that the cell wall is faintly scrobiculate.


Zygospore of C. granatum. Notice short, blunt spines.

SEM picture of a zygospore of C. granatum. Notice short, blunt spines arising from a pyramidate base.

SEM picture of C. granatum in more detail showing scattered cell wall pores.