Meadowsweet rust

Meadowsweet rust (Triphragmium ulmariae) develops as a chemically induced swelling, arising from the lower surface of the leaves of meadowsweet.

Symptoms
The fungus attacks the petioles and / or midribs of the perennial Meadowsweet (Filipendula ulmaria) plant, a member of the Rosaceae family, causing swelling and distortion. Clusters of sporangia develop with bright orange spores.