Sisymbrium altissimum L. (syn.: S. sinapistrum Crantz) (E-Eur., W- and C-As.) – A rather rare but much increasing, locally naturalised alien. Apparently first documented as a wool alien in the valley or river Vesdre near Verviers in 1840. From 1860 (Aalst) onwards repeatedly observed in numerous and widely scattered locations. Often more or less persistent for some time and readily becoming naturalised. Rather well-documented from the border of river Meuse near Visé (known at least since 1885 and already extremely abundant around 1918). Also reported as naturalised around Brussel since the beginning of the 20th century (Schaarbeek, Vilvoorde; see also Vanden Berghen 1998). At present more or less widely naturalised with dense concentrations in urban areas, mainly near Antwerpen, Brussel and Gent (Verloove 2006a). Possibly less common in parts of Wallonia.
Sisymbrium altissimum usually occurs in dry, sunny habitats (often on sandy or gravelly substrate): pavement in urban areas, railway yards, canal banks, waste land, road verges, etc. More rarely seen in slightly disturbed natural habitats, for instance coastal dunes or gravelly river banks. Early records of Sisymbrium altissimum have been associated with wool and, more important, grain. Nowadays, it is still frequently observed in the surroundings of grain mills and in port areas.
The very similar Sisymbrium septulatum might have been overlooked, especially as a grain alien (see also under that species). It is larger in all its floral parts but is otherwise much reminiscent of Sisymbrium altissimum.
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Selected literature: Brandes (1990), Vanden Berghen (1998), Verloove (2006a).
Brandes D. (1990) Verbreitung, Oekologie und Vergesellschaftung von Sisymbrium altissimum in Nordwestdeutschland. Tuexenia 10: 67-82.
Vanden Berghen C. (1998) Note sur une station de Sisymbrium altissimum L. Adoxa 18: 1-2.
Verloove F. (2006a) Sisymbrium altissimum. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 835.