Phylum: Charophyta   Family: Desmidiaceae

Cosmarium integrum (P.M. Lundell) P.F.M. Coesel & K.J. Meesters 2023

Until recently this was a variety of Cosmarium holmiense. Semicells subtrapeziform with broadly rounded basal and apical angles and a well-marked constriction just below the apex, sides slightly convex with up to two undulations, apex broadly rounded. Cell-wall smooth with small to medium pores. Chloroplast axile with usually ten longitudinal ridges, seen best in apical view, and one pyrenoid. It differs from C. holmiense in having up to two undulations below the apical constriction as apposed to four and is much commoner.
Cell dimensions: L: 45-56 µm, B: 28-32 µm, Is: 18-21 µm; Th: 22-25 µm; L/B: 1.5-1.8.
A common taxon found in habitats that are subject to desiccation such as wet moss, ephemeral pools and shallow depressions.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.