This is the early stage of one of two rust fungi which attack Conopodium majus (Pignut); the later stages attack the unrelated plant Persicaria bistorta (Common Bistort); another rust which does not 'gall' the Pignut and which sometimes occurs on the same leaves is Puccinia tumida. This stage - the aecial stage - also attacks Angelica sylvestris (Wild Angelica).