Phylum: Charophyta   Family: Closteriaceae

Closterium rostratum Ehrenberg ex Ralfs

Widespread but infrequently recorded in the Outer Hebrides. Generally, an acidophile of boggy water with mosses but also tolerant of less acidic conditions

References: 
Brook, A.J. & Williamson, D.B. (2010) A Monograph on some British Desmids
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
Prescott, W.G., et al. (2001 reprint) A Synopsis of North American Desmids. Part II, Desmidiaceae: Placodermae, Section 1