Phylum: Charophyta   Family: Closteriaceae

Closterium upsaliense (C.F.O. Nordstedt) P.F.M. Coesel & K.J. Meesters 2023

First described by Nordstedt in Wittrock et al. (1889: 47) as Closterium cornu var. upsaliense. Recently, it was raised to species level by Coesel & Meesters (2023: 63, pl. 10: 26-27). It differs from Closterium cornu in being narrower without overlap and also shorter with very little overlap. It also differs in having horned zygospores. Van Westen (2024: 134 & 133) has found both species in Drenthe, Netherlands, in newly constructed pools with sandy bottoms, which he suggests might indicate pioneer species.
Cell dimensions: L: 40-86 µm; B: 4.5-7 µm; Ap: 2-3 µm; L/B: 12-18.
Rarely recorded in the Outer Hebrides. Significantly, the image below that is undergoing division was found with bryophytes on wet rocks.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Ruzicka, J. (1977). Die Desmidiaceen Mitteleuropas, Volume 1, Part 1.
Van Westen, M. (2024). Sieralgen in Drenthe.
Wittrock, V.B., Nordstedt, C.F.O. & Lagerheim, G. (1889). Algae aquae dulcis exsiccatae praecipue scandinavicae quas adjectis algis marinis chlorophyllaceis et phycochromaceis.