The rust fungus Puccinia chrysosplenii affects Opposite-leaved Golden-saxifrage (Chrysosplenium oppositifolium) and Alternate-leaved Golden-saxifrage (C. alternifolium).  There is no host alternation, and only telia are produced.  The telia are mainly on the leaf undersides and of two types.  In spring and summer, telia are light brown, becoming grey as the long-pedicelled teliospores mature.  The second type over-winters, and has small, powdery, brown telia with two-celled spores on short deciduous pedicels.   This species is not listed in Redfern & Shirley (2023) as a gall-causer.

host

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

on Golden-saxifrages - in wet woodlands, flushes and damp shaded places