Puccinia poarum

Puccinia poarum is a species of rust fungus known as the coltsfoot gall rust or meadow grass rust, and it is a plant pathogen. On coltsfoot, Tussilago farfara, it forms a yellow to orange gall 1 to 2 centimetres across on the underside of the leaves, with 20 to 30 cup-shaped aecia on each gall and often a purple margin and central hole. It also infects grasses of the family Poaceae without forming galls, and it has been reported on at least seventy plant hosts, so it is a genetically diverse species. It was first found on Poa fertilis and Poa nemoralis in Denmark in 1877. Its life cycle needs two hosts: spermagonia and aecia form on coltsfoot, and uredinia and telia on a grass. Peter Nielsen first described this heteroecious cycle. In the United Kingdom the rust is locally common and widely distributed.