Phylum: Charophyta   Family: Desmidiaceae

Cosmarium porteanum W. Archer 1860

This species was named for George Porte (1819-1892) and the spelling corrected accordingly from C. portianum under which name most records can be found. It’s similar to the recently described C. porteaniforme F.A.C. Kouwets but differs from that species in having more or less truncate apices to the sinuses, which are open and parallel to start with. It also has smaller granules resulting in 10-13 vertical rows in face view. C. porteaniforme has 8-10 more robust granules.
Cell dimensions: L: 35.3-42.1 µm; B: 29.3-33.2 µm; Is: 10.5-12 µm; Th: c.18-20 µm; L/B: 1.21-1.32.
Fairly common in moorland pools and loch-margins, which are slightly acidic, mesotophic.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
Van Westen, M.C. (2024). Sieralgen in Drenthe.