Arabis L.
(excl. Fourraea Greuter et Burdet, Pseudoturritis Al-Shehbaz, Turritis L.)
Arabis, as currently understood (see Al-Shehbaz 2005, Mabberley 2008, Al-Shehbaz 2010), is a genus of ca. 70 species, mostly native to the northern hemisphere (predominantly Eurasian with some additional species in the Mediterranean area and in tropical Africa). Arabis has long been very broadly delimited and generic limits long remained very controversial. Recent molecular and cytological studies demonstrated that its representatives should be assigned to several different smaller genera that even belong to different tribes (Al-Shehbaz l.c.). In Belgium the following transfers were required: the native genera Turritis (with T. glabra L.; syn. Arabis glabra (L.) Bernh.) and Fourraea (with Fourraea alpina (L.) Greuter & Burdet; syn. Arabis pauciflora (Grimm) Garcke) need to be excluded from Arabis. The same is true for the non-native genus Pseudoturritis (with P. turrita (L.) Al-Shehbaz; syn.: Arabis turrita L.). In Belgium the remainder of the genus only counts two closely related native species, Arabis hirsuta (L.) Scop. and A. sagittata (Bertol.) DC. and a few additional non-native species. Several species of Arabis are popular ornamentals, especially for the rock garden (see Akeroyd 1995, Jäger & al. 2008 for an extensive account for Europe).
1. Mat-forming, procumbent perennial, with either distinct sterile rosettes or stolons. Petals 8-20 mm long === 2
1. Erect biennial or perennial, without or with indistinct sterile rosettes or stolons. Petals 4-8 mm long === 3
2. Leaf margin toothed. Entire plant densely grayish hairy with stellate hairs. Distinct sterile rosettes present. Petals ca. 10-20 mm long. Siliqua 20-70 mm long, patent === Arabis alpina
2. Leaf margin entire. Plant nearly glabrous or with scattered medifixed hairs on leaf margins only. Stolons present. Petals ca. 8-10 mm long. Siliqua 15-35 mm long, spreading === A. procurrens
3. Anthers 0,9-1,2 mm long. Leaves sessile, rounded at base and apex, margins dentate. Petals 6-8 mm long. Valves of siliqua with indistinct median vein === A. collina
3. Anthers 0,5-0,7 mm long. Leaves sessile to amplexicaul at base, acute to rounded at apex, margins nearly entire to dentate. Petals 4-6 mm long. Valves of siliqua with distinct median vein (native) === A. hirsuta and A. sagittata
Additional aliens: Arabis auriculata Lam. (syn.: A. recta Vill.) (Medit., C- and S-Eur., W-As., vector unknown) and A. planisiliqua (Pers.) Reichenb. (syn.: A. gerardii W.D.J. Koch, A. hirsuta subsp. gerardii Hartm.) (SW-Eur., vector unknown).
Literature:
Akeroyd J.R. (1995) Arabis. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 4. Cambridge University Press, Cambridge: 142-144.
Al-Shehbaz I.A. (2005) Nomenclatural notes on Eurasian Arabis (Brassicaceae). Novon 15: 519-524.
Al-Shehbaz I.A. (2010) Arabis. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 7. Oxford University Press, New York-Oxford: 257-266.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Jones B.M.G. (rev. by Akeroyd J.R.) (1993) Arabis. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1. Cambridge University Press, Cambridge: 352-356.
Karl R. & Koch M.A. (2013) A world-wide perspective on crucifer speciation and evolution: phylogenetics, biogeography and trait evolution in tribe Arabideae. Ann. Bot. 112: 983-1001.
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.
Lawalrée A (1957) Cruciferae. In: Robyns W. (ed.), Flore Générale de Belgique, vol. 2, fasc. 3. Jardin Botanique de l’Etat, Bruxelles: 287-404.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.