Phylum: Charophyta   Family: Closteriaceae

Closterium costatum var. borgei (W. Krieger) J. Ruzicka 1972

First described and illustrated by Willi Krieger (1935: 339, pl. 28: 11) as Closterium striolatum var. borgei. It was later moved by Ruzicka (1972: 458) to its current position. It differs little from the nominate variety except in having much finer striations (typically 5-7/10 µm).
Cell dimensions: L: 240-370 µm; B: 33-45 µm; Ap: 8-14 µm; L/B: 6-10.
Much rarer than the nominate variety but found in similar habitats; it has also been found with other algae in flowing water.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Krieger, W.. (1935). Die Desmidiaceen Europas mit Berücksichtigung der aussereuropäischen Arten. Band 13. Abteilung 1, Teil 1, Lieferung 2 of Dr. Rabenhorst's Kryptogamen-Flora von Deutschland, Österreich und der Schweiz.
Ruzicka, J. (1972). Die Zieralgen der Insel Hiddensee.