Phylum: Charophyta   Family: Desmidiaceae

Micrasterias americana Ehrenberg ex Ralfs 1848

West & West (1905, p. 117, pl. 53: 4-5 & pl. 54: 1-3) give a widespread distribution in Britain with several sites mentioned in Scotland but none for the Inner or Outer Hebrides. Recent sampling of slightly acidic oligotrophic water-bodies suggest it is rather scarce if not rare.

References: 
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands.
Ralfs, J. (1848) The British Desmidieae.
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2.