Cosmarium cataractarum
Image © Koos Meesters

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

Cell dimensions (L x B): 42 x 29 µm

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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.

Desmid of the month January 2016

Cosmarium cataractarum

Desmid of the month
January 2016