Phylum: Charophyta   Family: Desmidiaceae

Desmidium aptogonum Brébisson ex Kützing 1849

An acidophile of moorland bogs and pools, also shallow lochans. The Wests & Carter (1923) reported it as widespread in suitable habitats but not common. This would still seem to be the case for the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5