Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus extensus var. rectus (B. Eichler & M. Raciborski) P.F.M. Coesel & K.J. Meesters 2013

Predominantly a biradiated species with an extended isthmus from slight to quite marked, which alters the shape of the semicells from subtriangular to subrectangular. Spines appear at the lateral-apical angles and are predominantly parallel.
Cell dimensions (3): L: 18-24 µm; B: 17-24 µm; Is: 6.5-7.8 µm; Sp: 7-14 µm; Overall B: 38-53.
Found in acidic moorland pools and loch-margins. Rarely recorded in the Outer Hebrides.

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.