Phylum: Charophyta   Family: Closteriaceae

Closterium angustatum var. sculptum (M. Raciborski) J. Ruzicka 1977

First described and illustrated by Raciborski (1889: 75, pl. 7: 19) as Closterium intermedium var. sculptum. It was later moved by Ruzicka (1977: 227, pl. 34: 5) as a variety of C. angustatum. It differs from the nominate in that the striae (costae) have the crests interrupted with thickenings giving a corrugated or knotted appearance. Brook & Williamson (2010: 204) comment: “Found only in acid environments similar to those inhabited by the nominal variety.”
Cell dimensions: L: 300-450 µm; B: 19-25 µm; Ap: 10-15 µm; L/B: 11-20.
Current finds from the Outer Hebrides were in slightly acidic waters, which is contrary to Brook & Williamson’s comments above. It would appear to be very scarce with few recent finds.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Raciborski, M. (1889). Nowe Desmidyje.
Ruzicka, J. (1977). Die Desmidiaceen Mitteleuropas, Volume 1, Part 1.