C. cataractarum. Notice pyramidal outline of the semicells. Chloroplast with a single, central pyrenoid.

Cell dimensions (L x B): 42 x 29 µm



Desmid of the month
January 2016

Cosmarium cataractarum

C. cataractarum, better known under the name of C. variolatum var. cataractarum*, is characterized by medium-sized, smooth-walled cells the semicells of which have a pyramidal outline. One of the most characteristic features is the cell wall sculpturing: coarsely scrobiculate with an extra large, deep pit in about the semicell centre. C. cataractarum is encountered in various neutral-alkaline, meso-eutrophic habitats. In the Netherlands, although only recognized in 2008, it appears to be fairly widely distributed.

*For a taxonomic discussion, see:
Šťastny, J. & Kouwets, F.A.C. (2012) New and remarkable desmids (Zygnematophyceae, Streptophyta) from Europe: taxonomical notes based on LM and SEM observations. Fottea 12: 293–313.

Empty semicell of C. cataractarum showing scrobiculate cell wall and large, deep pit somewhat below the centre.

SEM picture of C. cataractarum showing cell wall sculpturing in detail.