Phylum: Charophyta   Family: Desmidiaceae

Cosmarium cucumis Corda ex Ralfs

An acidophile found on moorland pools and Sphagnum bogs. Described as common in the north-west of Scotland but scarce, or elusive, for the Outer Hebrides

References: 
Ralfs, J. (1848) The British Desmidieae
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles