Ligularia dentata  

Ligularia dentata (A. Gray) H. Hara (syn.: L. clivorum Maxim., Senecio clivorum (Maxim.) Maxim.) (E As.) – A rare, locally more or less persisting escape from cultivation (or often a mere throw-out). First documented from damp rough ground in Gavere in 2010 and there repeatedly confirmed subsequently. Recently also recorded in Berchem, Geel, Kalken and Meerhout. See here for an overview of Belgian records: http://waarnemingen.be/soort/view/119374.

Ligularia dentata is sometimes found in neighboring territories as well, for instance in the British Isles (Stace 2010).

Farfugium japonicum (L.) Kitam. (syn.: Ligularia tussilaginea (Burm. f.) Makino) is a very similar species and is also cultivated as an ornamental. Its leaf margins, however, are distinctly revolute and its achenes hairy (vs. more or less flat leaf margins and glabrous achenes in Ligularia dentata).

Selected literature:

Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.