gallers on Thesium

1a Malformations of complete shoots or extended systems of shoots => 2

1b Stem, mainly close to ground, with sometimes bent, bulging swellings, on their surface with scale insects in single to several rimmed depressions. T. bavarum, humifusum: Planchonia arabidis

1c Yellow, rough nodular swellings, 2–8 mm across, clustered on root collar. T. humifusum: Unidentified weevi

2a Shoots completely pervaded and ± disfigured by perennial mycelium of a rust fungus. Aecia, unopened longer than wide, often ± red-brown coloured, occurring on both sides of leaf, on stems, occasionally also on bracts and flowers => 3

2b Inflorescence usually largely disfigured; excessive branching and leafiness; phyllanthy. T. alpinum, divaricatum, humifusum, linophyllon: Aceria anthonoma

3a The three monoecious rust fungi occurring on Thesium cannot be distinguished according to their aecia. Uredina easily detached, their sori later on ± with dusting. Aecia often rare or almost absent => 4

3b Teliospores glabrous, on compact stalks; sori compact. Aecia often present. Thesium spp.: Puccinia thesii

4a Fungus mainly on T. alpinum and T. linophyllon: Puccinia mougeotii

4b On several other Thesium species, mainly on T. ebracteatum: Puccinia passerinii