Linaria simplex (Willd.) DC. (Medit., Atlan. Isl.) – A very rare alien but possibly increasing. Recorded in the 19th century without further details (Durand 1899). In 2013 discovered in bare, gravelly soil at the tramway in Jette (Brussels). At this locality confirmed in 2014 and apparently slightly spreading. A local naturalization is not unlikely: the species is abundantly fruiting before herbicides are applied.
Linaria simplex is progressively expanding to the north and has reached in the past decades parts of northern France (e.g. Berchtold 1998, Weiss & Pax 2006, Verloove & Lambinon 2014). It is often found adjacent to railway tracks which probably explains its recent expansion.
Linaria simplex is closely related to native L. arvensis and both mainly differ in flower color.
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Selected literature:
Berchtold J.-P. (1998) Linaria simplex, une Linaire nouvelle pour la flore d'Alsace. Bull. Ass. philomat. Alsace Lorraine 34: 33-36.
Durand T. (1899) Phanérogames. In: De Wildeman E. & Durand T., Prodrome de la flore belge. A. Castaigne Editeur, Bruxelles: 1112 p.
Verloove F. & Lambinon J. (2014) La sixième édition de la Nouvelle Flore de la Belgique:
commentaires chorologiques. Dumortiera 104: 41-73. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_104/Dum_104_41-73_NF-6_Chorologie.pdf]
Weiss J.M. & Pax N. (2006) Le coin des découvertes. Willemetia 50: 1. [available online at: http://www.floraine.net/fileadmin/floraine/Publications/WILLEMETIA/2006/Willemetia_50.pdf]