Phylum: Cyanobacteria   Family: Chroococcaceae

Chroococcus turgidus (Kützing) Nägeli

Common with Sphagnum and other acidic habitats

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011) - The Freshwater Algal Flora of the British Isles