British distribution: Widespread, frequent.
A heteroecious rust with spermogonia and aecidia usually on Dog's Mercury (Mercurialis perennis), less often on Annual Mercury (Mercurialis annua), and apparently rarely on Larch (Larix) and Pine (Pinus). The uredinial and telial stages are on poplars: White Poplar (Populus alba), Aspen (P. tremula) and Grey Poplar, their hybrid, (P. × canescens).
Wilson & Henderson (1966) give old records for occurrence on Larch and the FRDBI contains a single record on Larch from 1884. British records on Pine are also few, though it has been known on at least three species, P. nigra, P. sylvestris and P. pinaster. Mercurialis perennis is overwhelmingly the dominant aecial host here.
Termorshuizen & Swertz (2011) list Corydalis species and Chelidonium majus (Greater Celandine) as additional aecial hosts, but such records refer to a related rust, Melampsora magnusiana, which is not known in Britain.
For an explanation of the terms used in this account, go to the profile of the Pucciniales.