Centaurea calocephala Willd. (syn.: C. atropurpurea Waldst. & Kit.) (SE Eur.) – An exceptional escape from cultivation. Two individuals were found growing on a demolition site in Laakdal in 2014.
Despite being fairly showy, this species is only rarely cultivated as an ornamental. It is not treated in most recent garden floras (e.g. Cullen 2000, Jäger & al. 2008).
Selected literature:
Cullen J. (2000) Centaurea. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 530-534.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Pop I. (1975) Studium über die Taxonomie, Chorologie und Zönologie der Art Centaurea atropurpurea W. et K. Phytocoenologia 2(1-2): 49-53.