Phylum: Charophyta   Family: Desmidiaceae

Cosmarium porteaniforme F.A.C. Kouwets 2025

This recently described species differs from C. porteanum in having oblique apices to the sinuses that widen from the start. It also has larger granules resulting in 8-10 vertical rows in face view. C. porteanum has 10-13. It also has a greater L/B ratio but there is overlap.
Cell dimensions (2): L: 36-37.5 µm; B: 26.3-28.9 µm; Is: 10.1-11.9 µm; Th: c.20-22 µm; L/B: 1.30-1.37.
Being recently described, only two cells have been found to date. One was from semi-permanent rain-water pools in a disused quarry, which was slightly alkaline.

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