A common rust fungus throughout Britain that primarily attacks Bramble Rubus fruticosus. The early stage (uredinial) appears as a yellow power followed in late summer by the dark telial stage that overwinters.

References: 
Termorshuizen, A.J. & Swertz, C.A. (2011). Dutch Rust Fungi.
Wilson, M. & Henderson, D.M. (2011 reprint). British Rust Fungi.