Phylum: Cyanobacteria   Family: Nostocaceae

Nostoc commune  Vaucher ex Bornet & Flahault

Colonies start small and almost globular but soon develop in quite large colonies several centimeters across. Found in a broad range of habitats with sufficient moisture

References: 
John, Whitton & Brook (2011) - The Freshwater Algal Flora of the British Isles