Great Burnet Rust (Xenodochus carbonarius) causes galls on the leaves of Great Burnet (Sanguisorba officinalis).  There is no host-pant alternation.  Swollen purple spots on leaf undersides and petioles bear orange aecia; later, black telia are produced on both surfaces of leaves.

host

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

on Great Burnet, meadows and wet grasslands