Phylum: Charophyta   Family: Desmidiaceae

Cosmarium benedictum F. Ducellier 1919

Semicells almost quadrate at the base with a rounded apex. Sides and apex slightly undulate. Isthmus shallow and slightly open. Chloroplast axile with one large pyrenoid. Zygospore globose, ornamented with short protuberances on swollen bases.
Cell dimensions: L: 42-50 µm, B: 24.5-33.5 µm, IS: 18-24 µm; Th: 20-21.5 µm; L/B: 1.5-1.8.
Zygospore diameter: 38-40 µm without spines, 52-55 µm with spines.
A rare species found in habitats liable to periodic drying such as ephemeral pools and wet rocks. The taxonomy is complicated and I refer you to Kouwets (in manuscript) for a detailed analysis.

References: 
Ducellier, F. (1919) Deux Desmidiacées nouvelles.
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium.
Van Geest, A. & Coesel, P.F.M. (2019) Some new and interesting desmids (Streptophyta, Desmidiales) from ephemeral puddles in the urban and industrial areas of Amsterdam (Netherlands).