Phylum: Charophyta   Family: Desmidiaceae

Staurastrum merianii  Reinsch

An Arctic/alpine species confined to the north-west in Britain. It would seem not too scarce in the Wests' (1912) time but few records reported now and quite likely rare. The habitat is shallow, vegetated, pools and cuttings but also with bryophytes on dripping rocks

References: 
West, W. & West, G.S. (1912) A Monograph of the British Desmidiaceae, Volume 4
Prescott, W.G., et al. (2001 reprint) A Synopsis of North American Desmids. Part II, Desmidiaceae: Placodermae, Section 4
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus