Puccinia cnici-oleracei is a rust fungus that affects the leaves of Marsh Thistle (Cirsium palustre) in VC55, and on Melancholy Thistle (Cirsium heterophyllum) in other areas. There is no host alternation, and only the dark-brown telia are found, on slightly thickened yellowish spots.  

Taxonomy is confusing.  Some authors consider the rust on Achillea millefolium to be a distinct species, Puccinia millefolii, and we have set up a separate gallery page for this species.

host

Photograph the rust on the host.  Ensure you have noted the host-plant species in your comments. On some hosts, microscopic examination may be needed.

on Marsh Thistle, and other thistles

Plant Parasites of Europe