Phylum: Cyanobacteria   Family: Rivulariaceae

Dichothrix gypsophila Bornet & Flahault, 1886

Usually found on hard surfaces but occasionally on plant material. Well distributed in freshwater

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