Cosmarium difficile. Notice rather small cell dimensions and hexagonal outline of the semicells.

Cell dimensons (L x B): 24 x 16 µm



Desmid of the month
May 2019

Cosmarium difficile

C. difficile is a rather small-sized, smooth-walled Cosmarium species with (in frontal view) more or less hexagonal semicells. Its most important diagnostic feature is in the distribution of cell wall pores, viz in three transversal rows: one at the apex, one in the middle part and one at the base of each semicell.
High magnification of empty cells reveals a scrobiculate character of the cell wall.
Zygospores are globose and furnished with broadly rounded, conical protuberances. In the Netherlands, C. difficile is a rather common species in slightly acidic, mesotropic habitats. Zygospores are only known from a single site.

Another cell of C. difficile showing a central pyrenoid in each semicell.

Empty cell of C. difficile showing transversal series of cell wall pores.

SEM picture of C. difficile showing a scrobiculate cell wall and in each semicell an apical, a median and a basal series of cell wall pores.

Image Hanny Kooijman née Van Blokland © IBED
Another SEM picture of a C. difficile cell showing that the cell wall pores in the median series are much closer to each other than in the apical and the basal series.


Zygospore of C. difficile. Notice stout, broadly rounded, conical protuberances.