Rorippa Scop.
Rorippa, as currently understood (excl. Nasturtium R. Brown), comprises ca. 85 species and is subcosmopolitan. Three species are more or less widespread natives in Belgium: Rorippa amphibia (L.) Besser, R. palustris (L.) Besser and R. sylvestris (L.) Besser. Hybridization frequently occurs where two or more taxa grow together. In Belgium hybrids have rarely been reported and, so far, only Rorippa xanceps (Wahlenb.) Reichenb. (R. amphibia x R. sylvestris) is involved.
In the past decades Nasturtium (with only native members in Belgium) was often included in Rorippa but molecular phylogenetic research proved that it should be maintained as a separate genus (Al Shehbaz & Price 1998). It is, in fact, more closely related to Cardamine than it is to Rorippa.
- Silicula subglobose (nearly as wide as long), 1,5-3 mm long with persistent style ca. as long as the silicula. Upper leaves sessile-amplexicaul, entire or irregularly and shallowly toothed === 1. Rorippa austriaca
- Silicula elleptical (obviously longer than wide) with style shorter than the silicula. Leaves never sessile-amplexicaul and subentire (native) === R. amphibia, R. palustris and R. sylvestris
Additional alien: Rorippa stylosa (Pers.) Mansf. et Rothm. (syn.: R. pyrenaica auct. non (All.) Reichenb. (C and S-Eur., wool,… alien).
Literature:
Al-Shehbaz I.A. (2010) Rorippa. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 7. Oxford University Press, New York-Oxford.
Al-Shehbaz I.A. & Price R.A. (1998) Delimitation of the genus Nasturtium (Brassicaceae)., Novon8(2): 124-126.
Bleeker W., Weber-Sparenberg C. &Hurka H. (2002) Chloroplast DNA variation and biogeography in the genus RorippaScop. (Brassicaceae). Plant Biology4(1): 104-111.
Jonsell B. (1968) Studies in the North-West European species of Rorippa s.str. Symb. Bot. Upsal.19(2): 1-222.
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.
Stuckey R.L. (1972) Taxonomy and distribution of the genus Rorippa (Cruciferae) in North America. Sida4: 279-430.
Valentine D.H. (rev. Jonsell B.) (1993) Rorippa. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1 (2nd ed.). Cambridge University Press, Cambridge: 344-345.