The gall-causing rust fungus Puccinia primulae affects the leaves of Primrose causing slightly thickened pale yellow blotches on the upper sides of the leaves with orange aecia under the leaves.  There is no host alternation.  Rust-coloured uredinia and dark brown telia are present later.

host

Photograph the rust on the host.  Ensure you have noted the host-plant species in your comments

on Primroses