A gall-causing smut fungus found on Celandine.  Pustules form on the petioles and leaves, containing a sooty mass of spore balls. The spore balls are clusters of one or more spores surrounded by several sterile cells.  The spore balls have a bubbly appearance at high magnification.

host

Photograph the gall on the celandine leaf; we recommend that the spores are examined.  Note the host species in your comments, and ensure your photos show the dark spore mass.

Celandines

Rare

See Plant Parasites of Europe webpage (Bladmineerders)