Achillea ageratum L. (W-Medit.) – A very rare escape from cultivation. Formerly naturalized in the surroundings of a dump in Kessel-Lo near Leuven, at least between 1952 and 1970. In 1954 also found on a dump in Mechelen (Galgenberg) (Lawalrée 1956).
Achillea decolorans Schrad. (syn.: A. serrata Sm.) – probably a hybrid of A. ptarmica and A. macrophylla L. – is wrongly considered to be a synonym of A. ageratum by Thornton-Wood (2000).
Selected literature:
Lawalrée A. (1956) Phanérogames adventices ou naturalisées en Belgique. Bull. Soc. Roy. Bot. Belg. 88: 25-28.
Thornton-Wood S.P. (2000) Achillea. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 607-612.
Taxonomic name: