Phylum: Charophyta   Family: Peniaceae

Penium polymorphum (Perty) Perty

'A scarce but widely distributed desmid, found especially in upland and western regions of the British Isles in acid bogs and amongst Sphagnum' - Brook & Williamson (2010)

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
West, W. & West, G.S. (1904) A Monograph of the British Desmidiaceae, Volume 1