Cosmarium monomazum. Notice about circular cell shape and crenate outline caused by an intramarginal series of warts.

Cell dimensions (L x B): 33 x 35 µm

Empty cell of C. monomazum showing next to the intramarginal warts a central ornamentation characteristic of var. polymazum, viz. a big supraisthmial granule and a transversal series of three (composite) granules across the middle.



Desmid of the month
May 2020

Cosmarium monomazum

Cells of Cosmarium monomazum are medium-sized and about circular in outline. The species is primarily characterized by two series of emarginate warts extending over apex and lateral sides of the semicells. Those series are particularly distinctive in apical and lateral view. The best known variety, viz. var. polymazum, is marked by an additional ornamention consisting of a large, tubercle-like granule just above the isthmus, and three large granules (often partitioned into smaller ones) forming a transverse series across the middle of the semicell. Duch records of C. monomazum var. polymazum are confined to some oligo-mesotrophic moorland pools dating from the first half of the last century.

Cell of C. monomazum well showing the intramarginal series of emarginate warts.

Semicell of C. monomazum var. polymazum in apical view well showing the two series of warts extending over the apex just within each lateral margin.

Image © Jan Šťastný (after Irish material)

SEM picture of C. monomazum var. polymazum.