Coltsfoot Gall Rust

On Tussilago farfara (coltsfoot), infection by P. poarum results in large, circular, yellow or orange-red spots that protrude from the undersides of the leaves. The spots often have a purple margin, and sometimes a central hole. On the lower leaf surface, 20-30 cup-shaped aecia of the fungus form on each gall. On the upper surface of the leaf, infection results in a yellow circle with no swelling. Spermogonia may also be present. On Tussilago farfara, the rust is necrotrophic, obtaining nutrients from dead cells and plant tissues.

Identification. Puccinia poarum may be confused with a different rust on Tussilago farfara (coltsfoot), Coleosporium tussilaginis. Coleosporium tussilaginis usually appears later in the season and does not form galls or aecia, but instead forms diffuse uredinia with powdery orange spores on the lower leaf surface; it is less obvious on the upper leaf surface, and lacks the purple margin and central hole characteristic of P. poarum.

In the United Kingdom, this rust is locally common, and widely distributed. Northern hemisphere to South America.