Diplotaxis DC.
Literature: Schulz (1919), Martínez Laborde (1988), Martínez Laborde (1993), Heywood (rev. Akeroyd & Martínez Laborde 1993), Warwick & Black (1993), Eschmann Grupe & al. (2003), Warwick & Sauder (2005), Verloove & Lambinon (2008), Al-Shehbaz (2010).
As traditionally understood Diplotaxis is a genus of 27 species, native to Eurasia and the Mediterranean region. However, molecular data indicate a polyphyletic origin for Diplotaxis (and Brassica, Erucastrum and Hirschfeldia) (Warwick & Black 1993, Warwick & Sauder 2005). All these genera are probably better united in a single, broadly circumscribed genus. Pending additional studies and following Al-Shehbaz (2010) it is here provisionally maintained in its traditional circumscription. Two species (Diplotaxis muralis (L.) DC. and D. tenuifolia (L.) DC.) are usually considered to be native in Belgium but they are probably at most archaeophytes. The former might even be a relatively recent newcomer (see also Heywood 1993). Several species of Diplotaxis are reputed weeds of agricultural land and now have a more or less subcosmopolitan distribution.
Previous Belgian records of Diplotaxis viminea (L.) DC. turned out to be in error, mostly for D. muralis (Verloove & Lambinon 2008).
1. Petals white (often violet-veined) === Diplotaxis erucoides
1. Petals yellow === 2
2. Perennial with glabrous leaves, foetid when crushed. Petals ca. 8-14 mm long (native) === D. tenuifolia
2. Annual or biennial (rarely perennial), densely hispid to nearly glabrous, foetid or odourless. Petals ca. 6-8 mm long === 3
3. Leaves mostly basal. Annual, biennial or perennial, foetid when crushed. Beak of siliqua always seedless (native) === D. muralis
3. Stem leafy. Odourless annual. Beak of siliqua with 1-2 seeds === 4
4. Stem densely hispid below. Sepals horned === D. virgata
4. Stem sparsely hispid to nearly glabrous below. Sepals not or hardly horned === D. catholica
References
Al-Shehbaz I.A. (2010) Diplotaxis. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 7. Oxford University Press, New York-Oxford: 432-433.
Eschmann Grupe G., Hurka H. & Neuffer B. (2003) Species relationships within Diplotaxis (Brassicaceae) and the phylogenetic origin of D. muralis. Plant Syst. Evol. 243(1-2): 13-29.
Heywood V.H. (rev. Akeroyd J.R. & Martínez Laborde) (1993) Diplotaxis. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1 (2nd ed.). Cambridge University Press, Cambridge: 404-405.
Martínez Laborde J.B. (1988) El género Diplotaxis (Cruciferae) en España. Lagascalia 15 (extra): 243-248.
Martínez Laborde J.B. (1993) Diplotaxis. In: Castroviejo S. & al. (eds), Flora Iberica Vol. 4. Consejo Superior de Investigaciones Científicas, Madrid : 346-362.
Schulz O.E. (1919) Diplotaxis. In: Engler A. (ed.), Das Pflanzenreich 70(IV.105). Engelmann, Leipzig: 149-180.
Verloove F. & Lambinon J. (2008) Neophytes in Belgium: corrections and adjustments. Syst. Geogr. Pl. 78: 63-79.
Warwick S.I. & Black L.D. (1993) Molecular relationships in subtribe Brassicinae (Cruciferae, tribe Brassiceae). Can. J. Bot. 71: 906-918.
Warwick S.I. & Sauder C.A. (2005) Phylogeny of tribe Brassiceae (Brassicaceae) based on chloroplast restriction site polymorphisms and nuclear ribosomal internal transcribed spacer and chloroplast trnL intron sequences. Canadian Journal of Botany 83(5): 467-483.