Phylum: Charophyta   Family: Desmidiaceae

Euastrum didelta Ralfs

Very similar to E. humerosum but that species has the basal lobes with an indent, whereas in this species they are entire. The Wests (1905) say "Common in Outer Hebrides". Found in acidic oligotrophic waters such as moorland pools and peat bogs.

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