Phylum: Charophyta   Family: Desmidiaceae

Cosmarium quadratiforme F.A.C. Kouwets 2025

This recently described species was part of the Cosmarium quadratum Ralfs 1848 complex. It is on average a little smaller and has a markedly narrower isthmus.
Cell dimensions: L: 50.8-54.4 µm; B: 28.3-31.8 µm; Is: 17.4-18.9 µm; Th: c.22-25 µm; L/B: 1.64-1.93.
Because of the foregoing the status is uncertain. It would seem to prefer subatmophytic habitats such as with moss and liverworts on dripping rocks, and also in semi-permanent rainwater pools.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.