Phylum: Charophyta   Family: Desmidiaceae

Staurastrum brevispina J. Ralfs 1848

Cells medium-sized with a closed sinus at the start then opening widely. Semicells broadly elliptical to oval with the apices retuse to convex. At the median line of the semicells is a small papilla. In apical view 3-radiate with concave sides and broadly rounded angles. A variable species with a cloudy distinction between this nominate variety and St. brevispina var. boldtii Lagerheim 1893.
Cell dimensions: L: 34-41 µm; B: 30-40 µm; Is: 9.6-14 µm; L/B: 1.06-1.23.
Prefers slightly acidic habitats and found in the plankton of shallow, vegetated lochs. Widespread in the Outer Hebrides but not that common.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Van Westen, M.C. (2024). Sieralgen in Drenthe.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.