Protomyces macrosporus is an ascomycete fungus that forms galls on Aegopodium podagraria, Anthriscus sylvestris, Angelica sylvestris, Daucus carota and some other members of the family Umbelliferae or Apiaceae, commonly known as umbellifers.

[3] The gall develops as a chemically induced swelling, arising from the surface of the leaf lamina, veins, mid-ribs, and petiole.

On the leaf lamina it forms yellowish bulges standing out on the upper surface, but missing the black sori that are typical of an otherwise similar gall caused by the rust fungus Puccinia aegopodii.

On veins, mid-ribs and petioles the gall appears as translucent yellow-white swellings that are often elongated and blister-like.

[6] The stem gall caused by Protomyces macrosporus is the most serious and widespread disease of coriander in the Chitwan valley of Nepal.