Phylum: Basidiomycota Family: Agaricaceae
Puccinia punctiformis (F. Strauss) Röhl.
Thistle Rust
Widespread and very common, especially on Creeping Thistle
References:
Ellis & Ellis (1997) Microfungi on Land Plants
Termorshuizen & Swertz (2011) Dutch Rust Fungi
Wilson & Henderson (2011) British Rust Fungi