The generic limits of Sisymbrium are currently under study. It traditionally included ca. 90 mainly Eurasian and Mediterranean species (with some additional species in South Africa and the New World). Recent molecular research accepts Sisymbrium in a narrower sense. As such, it counts about 40 species and is almost completely confined to the Old World; see Warwick & al. (2002), Warwick & al. (2005) and Al-Shehbaz (2010). An extinct native species, Sisymbrium supinum, is now transferred to Erucastrum (Warwick & Al-Shehbaz 2003). Sisymbrium s.str. further includes two native species in Belgium: the rare S. austriacum Jacq. subsp. austriacum and the very common S. officinale L. Many species of Sisymbrium are notorious weeds of arable land and have become nearly cosmopolitan weeds.
1. Strongly rhizomatous perennial, often somewhat glaucous. Ripe fruits rarely produced === Sisymbrium volgense
1. Annual or biennial (rarely perennial; if so never strongly rhizomatous). Usually not glaucous. Fruits normally produced === 2
2. Inflorescence bracteate, at least below (flowers nearly sessile in leaf axils) === S. runcinatum
2. Inflorescence ebracteate, flowers pedicellate === 3
3. Siliqua at most 20 mm long, closely appressed to stem (native) === S. officinale
3. Most siliqua longer (if occasionally less than 20 mm, than not closely appressed to stem) === 4
4. Fruiting pedicels thick, towards apex ca. as wide as siliqua === 5
4. Fruiting pedicels slender, distinctly narrower than siliqua === 8
5. Biennial to perennial. Siliqua 7-50 mm long, pedicels often strongly contorted === S. austriacum p.p.
5. Annual. Siliqua > 50 mm long, pedicels never contorted === 6
6. Outer sepals not cucullate (horned) near apex. Uppermost leaves not divided in linear segments === S. orientale
6. Outer sepals conspicuously cucullate near apex. Uppermost leaves divided in linear segments === 7
7. Sepals 4-6 mm long, subapical horn ca. 0,5 mm long. Petals 6-8 mm long, very gradually narrowed to claw === S. altissimum
7. Sepals 6-9 mm long, subapical horn ca. 1,5 mm long. Petals up to 15 mm long, with a very distinct claw === S. septulatum
8. Inflorescence overtopped by young siliqua. Petals tiny, hardly exceeding sepals, whitish to pale yellow. Anthers 0,5-0,7 mm long === S. irio
8. Inflorescence not overtopped by young siliqua. Petals distinctly longer than sepals, pure yellow. Anthers ca. 0,7-1,5 mm long === 9
9. Septum of siliqua white, opaque. Pedicels often strongly contorted === S. austriacum p.p.
9. Septum of siliqua hyaline. Pedicels always straight === S. loeselii
Additional aliens: Sisymbrium erysimoides Desf. (syn.: S. rigidulum Lag.) (SW-Eur., N- and E-Afr., SW-As., Macaronesia, wool alien) and S. strictissimum L. (C-Eur., W-As., vector unknown). The latter was formerly naturalised in the valley of riverlet Berwinne between Renoupré and Dalhem, at least between 1894 and 1919.
Al-Shehbaz I.A. (2006) The genus Sisymbrium in South America, with synopses of the genera Chilocardamum, Mostacillastrum, Neuontobotrys, and Polypsecadium (Brassicaceae). Darwiniana 44(2): 341-358.
Al-Shehbaz I.A. (2010) Sisymbrium. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 7. Oxford University Press, New York-Oxford: 667-671.
Ball P.W. (1993) Sisymbrium. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1. (2nd ed.). Cambridge University Press, Cambridge: 318-321.
Clement E.J. (1982) Aliens and adventives. Adventive news 22. Sisymbrium spp. in Britain. BSBI News 30: 10-12.
Schulz O.E. (1924) Sisymbrium. In: Engler A. (ed.), Das Pflanzenreich 86(IV.105). Engelmann, Leipzig: 46-157.
Warwick S.I. & Al-Shehbaz I.A. (2003) Nomenclatural notes on Sisymbrium (Brassicaceae). Novon 13: 265-267.
Warwick S.I., Al-Shehbaz I.A., Price A. & Sauder C.A. (2002) Phylogeny of Sisymbrium (Brassicaceae) based on ITS sequences of nuclear ribosomal DNA. Canad. J. Bot. 80: 1002-1017.
Warwick S.I., Sauder C.A. & Al-Shehbaz I.A. (2005) Molecular phylogeny and cytological diversity of Sisymbrium (Brassicaceae). In: Sharma K.A. & Sharma A. (eds.), Plant genome: biodiversity and evolution. Enfield, N.H., vol. 1, part C.: 219-250.