Centaurea stoebe L. (syn.: C. rhenana Boreau, C. maculosa Lam. subsp. rhenana (Boreau) Gugler) (C and SE-Eur.) – A very rare and usually ephemeral alien, sometimes temporarily persisting or more or less naturalized locally. First reported from Leuven between 1882 and 1886 (grassland at the city walls). In 1892 recorded on a quay in the port of Antwerp. Observed in 1936 on an old wall in Grand Marchin. In recent times sometimes sown in road verges and then rather easily escaping, for instance in Hooglede since 2006 (road verge and adjacent ruderal area near brick factory) or Zwevegem (former railway track). In 2010 also recorded in a gravelly road verge in the port of Zeebrugge (a single specimen, apparently spontaneous). In 2014 discovered in the Waaslandhaven in Beveren (most likely initially sown) and there more or less established.
The infraspecific variability of Centaurea stoebe in Belgium requires further study. In wild flower seed mixtures subsp. micranthos (Gugler) Hayek (syn.: subsp. australis (A. Kerner) Greuter) seems to be the usual taxon (see also Frank & John 2007). This probably also corresponds with the weedy, tetraploid race that also occurs in North America. According to Mráz & al. (2011) this taxon and Centaurea stoebe s.str. are possibly better accepted as two distinct species.
Selected literature:
Becker G. (2005) Centaurea stoebe subsp. stoebe in der sudostlichen Pfungstadter Gemarkung. Hess. Flor. Briefe 54(4): 64-67.
Clement E.J. (2002) More about Centaurea rhenana (and allies) in MW Yorks. BSBI News 89: 33-34 (+ frontcover). [available online at: http://archive.bsbi.org.uk/BSBINews89.pdf]
Frank D. & John H. (2007) Bunte Blumenwiesen – Erhöhung der Biodiversität oder Verstoss gegen Naturschutzrecht? Mitt. florist. Kart. Sachsen-Anhalt 12: 31-45. [available online at: http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/27911]
Kestler T. & Wiedemann H. (1982) Centaurea stoebe L. in Nordhessen. Hess. Flor. Briefe 31(2): 30-31.
Korneck D. (2004) Centaurea stoebe subsp. micranthos, Kleinkopfige Flockenblume, eine verkannte Sippe unserer Flora (vorlaufige Mitteilung). Hess. Flor. Briefe 53(1): 1-5.
Korneck D. (2006) Centaurea stoebe subsp. stoebe und subsp. australis in Sudhessen. Hess. Flor. Briefe 55(2-3): 21-30.
Korneck D. (2016) Pflanzengesellschaften mit Centaurea stoebe s.l. im Rheingebiet. Mitt. Badischen Landesvereins Naturkunde Naturschutz e.V. 22(1): 23-58.
Mráz P., Bourchier R.S., Treier U.A., Schaffner U.& Schärer H.M. (2011) Polyploidy in phenotypic space and invasion context: a morphometric study of Centaurea s.l. Intern. Journ. Pl. Sc. 172: 386-401. [available online at: http://www.unifr.ch/ecology/groupmueller/assets/files/Mraz%20et%20al%202...
Ochsmann J. (2000) Morphologische und molekularsystematische Untersuchungen an der Centaurea stoebe L.-Gruppe (Asteraceae-Cardueae) in Europa. Dissert. Bot. 324, J. Cramer, Berlin-Stuttgart: IX + 242 p.
Otisková V., Koutecký T., Kolář F. & Koutecký P. (2014) Occurrence and habitat preferences of diploid and tetraploid cytotypes of Centaurea stoebe in the Czech Republic. Preslia 86: 67-80. [available online at: http://www.preslia.cz/P141Otiskova.pdf]
Taylor J. (2000) Centaurea rhenana on a Yorkshire motorway. BSBI News 85: 45-46. [available online at: http://archive.bsbi.org.uk/BSBINews85.pdf]
Welss W., Reger P. & Nezadal W. (2008) Zur Verbreitung von Centaurea stoebe L. subsp. stoebe und Centaurea stoebe subsp. australis (A. Kern.) Greuter (Asteraceae) im Nürnberger Becken. Mitteilungen des Vereins zur Erforschung der Flora des Regnitzgebietes 2: 44-53. [available online at: http://www.regnitzflora.de/Band2/RegnitzFlora2_WelssRegerNezadal.pdf]