1. Rapistrum rugosum (L.) All. (C and S-Eur., N-Afr., SW-As.) – A rather rare but increasing, locally naturalized and fast spreading alien. First recorded around 1888 near Huy (border of river Meuse). Further repeatedly observed around Leuven before 1900 (Kessel-Lo, Wilsele, etc.) and as a wool alien in the valley of river Vesdre near Verviers (at least between 1894 and 1947). However, all early records apparently proved to be ephemeral. Its genuine naturalization probably started in the 1950’s on the borders of river Leie/Lys between Menen and Comines. Since then steadily increasing, at first mainly in West-Vlaanderen (especially around Roeselare) and in the port of Gent (see map in Verloove 2002). Rapistrum rugosum was not yet included in the Belgian distribution atlas (van Rompaey & Delvosalle 1978, 1979) which demonstrates its fairly recent naturalization. Apparently much less frequent in Wallonia. Rapistrum rugosum is chiefly associated with (former) grain importation. It is often abundantly naturalized near old grain mills. Formerly also introduced as a wool alien in the Vesdre valley. Rapistrum rugosum is now most often recorded on canal banks, in road verges, old sandpits, dumps or waste land. In Great-Britain it is increasingly found as an invasive species in chalk grasslands (Steven 1992, Penfold 1993).
Rapistrum rugosum is a very variable species, especially with regard to silicula shape, rugosity, rib prominence and length and thickness of pedicels (see Vasconcellos 1993, Lambinon & al. 2004, etc.). Its infraspecific variability is insufficiently known in Belgium. Moreover, the taxonomic value of the three currently recognized subspecies is possibly weak. According to Warwick (2010) distinguishing features vary considerably and intergradation occurs in such a wide array of combinations that it seems meaningless to recognize them without further study. Especially subsp. linnaeanum (Coss.) Rouy et Fouc. and subsp. orientale (L.) Arcang., the forms mostly seen in Belgium, seem poorly distinguished and are probably better accepted as synonyms. The three subspecies can be separated in the following key (after Lambinon & al. 2004):
1. Fruiting pedicel thick (up to 1,3 mm wide), about as long as lower segment of the silicula === subsp. rugosum
1. Fruiting pedicel slender (up to 0,7 mm wide), 1,5-6x as long as lower segment of the silicula === 2
2. Upper segment of the silicula 1,5-2,5 mm wide, shallowly ribbed === subsp. linnaeanum
2. Upper segment of the silicula 2-3 mm wide, deeply ribbed === subsp. orientale
References:
Baranda J. (1983) Sobre la nomenclatura de Rapistrum rugosum (L.) All subsp. linnaeanum (Cosson) Rouy et Fouc. An. Jard. Bot. Madrid 40(1): 278.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H.) (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Lemke D.E. & Worthington R.D. (1991) Brassica and Rapistrum (Brassicaceae) in Texas. Southwest. Nat. 36(2): 194-197.
Penfold F. (1993) Bastard Cabbage in chalk grassland. BSBI News 64: 20.
Robbrecht E. & Jongepier J.-W. (1989) De synantrope flora van het havengebied van Gent (België, Oost-Vlaanderen), waarnemingen van 1986 tot 1988. Dumortiera 44: 1-12.
Steven G. (1992) Rapistrum rugosum, Bastard Cabbage - a new threat to chalk grassland. BSBI News 62: 43.
Van Landuyt W. (2006) Rapistrum rugosum. 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: 744.
Van Rompaey E. & Delvosalle L. (1978) Atlas de la flore belge et luxembourgeoise. Ptéridophytes et Spermatophytes. Commentaires. Jardin Botanique National de Belgique, Meise: 116 p.
Van Rompaey E. & Delvosalle L. (1979) Atlas de la flore belge et luxembourgeoise. Ptéridophytes et Spermatophytes (2ième éd.). Jardin Botanique National de Belgique, Meise: 1542 cartes.
Vasconcellos J.C. (rev. Akeroyd J.R.) (1993) Rapistrum. In: Tutin T.G. & al. (eds.), Flora Europaea (2nd ed.), vol. 1. Cambridge University Press, Cambridge: 414-415.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Warwick S.I. (2010) Rapistrum. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 7. Oxford University Press, New York-Oxford: 440-441.
Wyse-Jackson P.W. (1983) Rapistrum rugosum (L.) All. in Ireland. Bull. Irish Biogeogr. Soc. 5: 15-18.