gallers on Petasites

1a Galls on above-ground parts => 2

1b Roots with several nodule-shaped, massive swellings. P. paradoxus: Meloidogyne hapla

2a Galls wart-, cushion- or bulge-like => 4

2b Extended malformations on the leaf blades => 3

3a Leaves mostly stunted, leaf blades markedly curved downwards, sometimes bag-like, undulating, curled. Rolls partially markedly thickened. P. hybridus: Inducer unknown

3b eaf blade parts strongly curved downward, curled, the site of infestation dark green close to the froth-covered nymph. P. hybridus: Philaenus spumarius

4a Less than 1 mm long, multicellular, usually yellow, sometimes coalescing warts on green parts situated close to the ground. Petasites spp.: Synchytrium aureum

4b Larger, cushion- or bulge-like malformations => 5

5a Rotund or oblong flat aecia cushions, in yellowish or reddish spots, up to about 6–10 mm long situated, on leaf blades and veins, rarely on petioles. Petasites spp.: Aecidium petasitidis

5b Rotund cushions, the underside clearly bulged, and occupied by dark brown telia. P. frigidus, paradoxus: Puccinia expansa