Phylum: Charophyta Family: Desmidiaceae
Cosmarium pseudonitidulum var. rotundatum Willi Krieger & Gerloff 1965
This species is one of very few smooth-walled Cosmaria of this size that has two pyrenoids per semicell. This variety differs in having the length only slightly longer than the breadth giving a quotient of about 1.13. It also presents a trapeziform outline. Apparently only known from France (Etang des Rablais) where it was first discovered and described (Manguin 1936). It's rare and little is known about its ecology and distribution.
Manguin, E. (1936) La flore algale de L’étang de Rablais (Sarthe). Contribution à la connaissance de la microflore d’un étang calcaire de l’Ouest de la France
Krieger, W. & Gerloff, J. (1962-9) Die Gattung Cosmarium