Phylum: Charophyta   Family: Desmidiaceae

Staurastrum ralfsii var. depressum (J. Roy & J.P. Bisset) P.F.M. Coesel & K.J. Meesters 2013

First described and illustrated by Roy & Bisset (1886: 237, pl. 268: 14) as Staurastrum orbiculare var. depressum. More recently it was moved to its current position by Coesel & Meesters (2013: 142, pl. 32: 11-18). Cells in the variety are about as long as broad, and smaller than the nominate.
Cell dimensions: L: 22-28 µm; B: 19-28 µm; Is: 7-8 µm.
Found in oligo-mesotrophic waters with a wide range of pH values. Not common.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Roy, J. & Bisset, J.P. (1886). Notes on Japanese desmids. - No. I.