Phylum: Basidiomycota Family: Pucciniaceae
Puccinia urticata F. Kern
Nettle Clustercup Rust
A widespread rust of Common Nettle Urtica dioica. It starts as orange blisters on leaves and stems, then develops raised fruiting-bodies, turning pinkish with age
References:
Ellis & Ellis (1997) - Microfungi on Land Plants
Termorshuizen & Swertz - Dutch Rust Fungi