The rust causes galls on the leaves of Willowherbs (Epilobium) and the whole plant appears paler than usual, with curled leaves.  There is no host alternation.  The upperside of the leaves is yellowed and distorted; orange aecia are present, usually on underside of leaf.  Brown uredinia and telia are present later.  

The uredinial and telial stages of Pucciniastrum epilobii also affect willowherbs.

host

Photograph the rust on the host, photograph both sdes of leaf and whole plant.  Ensure you have noted the host-plant species in your comments

on willowherbs