Phylum: Charophyta   Family: Desmidiaceae

Staurastrum gracile  Ralfs ex Ralfs

Widespread in the north-west in a mixed variety of freshwater habitats. Similar to S. boreale but that species is more 'chunky' whereas S. gracile has more drawn-out semicells

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles