1. Hesperis matronalis L. (C- and SE-Eur., SW-As.) – A rather rare but locally more commonly naturalised escape from cultivation. Known as such in Belgium since at least 1821 (Durand 1899). Rather well-documented from several locations, for instance from Roly (since 1886) and in the valley of riverlet Molignée (Falaen, Warnant, etc.) since 1889. Obviously much more widespread in Wallonia than in Flanders. In Flanders Hesperis matronalis is often ephemeral and only very locally naturalised, for instance in the valley of river Maas (Verloove 2006). Possibly also in or near old estates (as a relic of cultivation). Hesperis matronalis is naturalised in rather damp, nitrophilous usually shady places (woody riverbanks, hedges, clearings, etc.).
Petals of Hesperis matronalis are usually lilac, purple or violet in the wild but plants with white petals have also been recorded as escapes. Hesperis matronalis is a very variable species and belongs to a complex of numerous closely related (micro-) species (see Ball 1993). The exact identity of the plants currently found in Belgium requires further study. It is not impossible that more than one taxon is involved.
References
Durand T. (1899) Phanérogames. In: De Wildeman E. & Durand T., Prodrome de la flore belge. A. Castaigne Editeur, Bruxelles: 1112 p.
Dvorák F. (1982) Some results of the study of Hesperis matronalis L. from the Belanske Tatry Mountains. Biologia, Bratislava 37(5): 441-447.
Dvorák F. & Dadakova B. (1976) The chromosome morphology of Hesperis matronalis subsp. matronalis and related diploid taxa. Folia Geobot. Phytotax., Praha 11: 313-326.
Hodgkin E. (1971) The double rockets. J. Roy. Hort. Soc. 96(4): 188-189.