Lepidium draba L. (syn.: Cardaria draba (L.) Desv.) – A locally fairly common alien. Apparently first documented from the surroundings of Oostende in 1840. Soon afterwards recorded in several different locations throughout Belgium, at first often in or near gravel pits (Ath, Quenast). At present most frequent in coastal areas and near larger cities (Antwerpen, Brussel,…) (see Van Landuyt 2006b).
Lepidium draba usually grows in sunny and nitrophilous habitats (often on calcareous soils): ruderalised seadunes, canal and river banks, waste land, etc.
As a whole, the number of records of Lepidium draba slightly decreases (Van Landuyt 2006b). However, at least locally, it seems to increase, for instance in coastal dunes. Although present in this area since quite some time, Lepidium draba has much extended in recent times only and often forms very dense patches. Future invasive behaviour seems very likely, as has recently been reported from coastal dunes in the Netherlands as well (Weeda 2009).
Lepidium chalepense, with silicula longer than wide and rounded to cuneate at base (see Stace 2010), is very similar and might have been overlooked. It has been recorded as a casual alien in Sclesin in 1912. This species and others that are much reminiscent of Lepidium draba might have been overlooked. In North America Lepidium appelianum Al-Shehbaz (syn.: Cardaria pubescens (C.A. Mey.) Jarmolenko) has become a noxious and widespread weed (see Al-Shehbaz & Gaskin 2010 for differences between these species). The specific status of these species should not be questioned according to these authors since they differ not only morphologically but also cytologically.
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Selected literature:
Al-Shehbaz I.A. & Gaskin J.F. (2010) Lepidium. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 7. Oxford University Press, New York-Oxford: 570-595.
Mulligan G.A. & Findlay J.N. (1974) The biology of Canadian weeds, 3. Cardaria draba, C. chalepensis and C. pubescens. Canad. J. Pl. Sci. 54: 149-160. [available online at: http://pubs.aic.ca/doi/pdf/10.4141/cjps74-024]
Mummenhoff K. (1995) Should Cardaria draba (L.) Desv. be classified within the genus Lepidium L. (Brassicaceae)? Evidence from subunit polypeptide composition of RUBISCO. Feddes Repert. 106: 25-28.
Rich T.C.G. (1988) Lepidium L. Plant Crib 1988: 25-26.
Scurfield G. (1962) Cardaria draba (L.) Desv. (Biological Flora). J. Ecol. 50: 489-499.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Van Landuyt W. (2006b) Coronopus didymus. 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: 306-307.
Weeda E.J. (1999) Lepidium heterophyllum Bentham, ein Neophyt atlantischer Herkunft im nordwestlichen Deutschland und in der Niederlande. Abhandl. Naturwissenschaftlichen Verein Bremen 44: 455-466.
Weeda E.J. (2009) The role of archaeophytes and neophytes in the Dutch coastal dunes. J. Coast Conserv. 14(2): 75-79.