Sisymbrium runcinatum Lag. ex DC. (SW-Eur., N-Afr., W-As.) – An exceptional and ephemeral alien. Recorded only once on a railway yard in the port of Gent in 2004, along with numerous other grain aliens.
A very similar species, Sisymbrium polyceratium L., recently became more or less naturalised near Paris and seems to be on its way to Belgium (Lombard 2009).
Lombard A. (2009) Résultats d’herborisations en banlieue parisienne à Ivry-sur-Seine (Val-de-Marne) et ses environs. Monde Pl. 497: 5-11.