Phylum: Charophyta   Family: Desmidiaceae

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

First described and illustrated by Eichler & Raciborski (1893: 120, pl. 3: 22, 24) as Arthrodesmus incus f. rectus. Recently, Coesel & Meesters (2013: 26, pl. 13: 6-13) made this a variety of Staurodesmus extensus. Differs from the nominate variety in having predominantly parallel spines that are relatively short.
Cell dimensions: L: 18-24 µm; B: 17-24 µm; Is: 6.5-7.5 µm; Sp: 7-14 µm; Overall B: 39-48.
Found in mildly acidic moorland pools and loch-margins. Infrequently recorded in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Eichler, B. & Raciborski, M. (1893). Nowe gatunki zielenic.