Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus phimus (W.B.Turner) Thomasson

An acidophile found in plankton, moorland pools and disused peat-cuttings. It would seem to be rather scarce

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
Kouwets, F.A.C. (1999) A check-list of desmids (Chlorophyta, Zygnemaphyceae) of France