Cosmarium is a large genus of desmids (Desmidiaceae), a group of green algae closely related to the land plants (Embryophyta).[1][2] Members of this genus are microscopic and found in freshwater habitats around the world.[3]
The name Cosmarium comes from the Greek word κοσμάριον - kosmarion, meaning a small ornament.[4]
Prescott1981
was invoked but never defined (see the help page).