Melampyrum L.
Melampyrum is a genus with ca. 35 species, all native in the northern hemisphere. The genus is particularly well-represented in Europe, especially in the Balkan Peninsula (Soó & Webb 1972, Mabberley 2008). In Belgium three species are considered native (M. arvense L., M. pratense L. and M. cristatum L.) (Lambinon & Verloove 2012). The latter, however, occurs on the extreme limits of its distribution area and has only been recorded in very few, isolated localities, all close to the frontiers with France and Luxembourg. A fourth species, N. nemorosum L., has been recorded as an alien.
Molecular studies have shown Melampyrum to be monophyletic (Bennett & Mathews 2006) and as sister to the rest of the Rhinantheae (Scheunert & al. 2012).
Melampyrum is a taxonomically complex genus in which species boundaries and infraspecific variability are poorly understood. Some authors tend to see species in Melampyrum as complexes of closely similar micro-species. Much of the variation, however, seems to be solely related to phenology (spring vs. summer flowering) and ecology (lowland vs. mountainous taxa) (Jäger & Werner 2005, Tison & de Foucault 2014).
1 Inflorescence dense, not unilateral, with closely imbricate floral bracts concealing the inflorescence axis (native) === Melampyrum arvense and M. cristatum
Inflorescence lax, unilateral, floral bracts not concealing inflorescence axis == 2
2 Floral bracts violet-blue. Calyx uniformly and densely hairy === M. nemorosum
Floral bracts green. Calyx glabrous or with some hairs on the veins only (native) === M. pratense
References:
Beauverd G. (1916) Monographie du genre Melampyrum L. Mém. Soc. Phys. Genève 38: 291-657. [available online at: http://www.biodiversitylibrary.org/bibliography/76042#/summary]
Bennet J.R. & Mathews S. (2006) Phylogeny of the parasitic plant family Orobanchaceae inferred from phytochrome A. American Journal of Botany 93(7): 1039–1051. [available online at: http://www2.huh.harvard.edu/research/mathews-lab/LabWebsite/pdfs/2006ajb...
Jäger E.J. & Werner K. (eds.) (2005) Rothmaler Band 4. Exkursionsflora von Deutschland. Gefässpflanzen: Kritischer Band. Springer Verlag, Berlin: 880 p.
Lambinon J. & Verloove F. (avec coll. Delvosalle L., Toussaint B., Geerinck D., Hoste I., Van Rossum F., Cornier B., Schumacker R., Vanderpoorten A. & Vannerom H.) (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Romero T. (2009) Melampyrum. In: Castroviejo S. (ed.), Flora Iberica, vol. 9. Real Jardín Botánico, Madrid: 440-451. [available online at: http://www.floraiberica.es/floraiberica/texto/pdfs/13_144_22_Melampyrum....
Scheunert A., Fleischmann A., Olano-Marín C., Bräuchler C. & Heubl G. (2012) Phylogeny of tribe Rhinantheae (Orobanchaceae) with a focus on biogeography, cytology and re-examination of generic concepts. Taxon 61(6): 1269-1285. [available online at: https://www.researchgate.net/publication/281691099_Phylogeny_of_tribe_Rh...
Soó R. & Webb D.A. (1972) Melampyrum. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 253-257.
Tison J.-M. & de Foucault B. (coord.) (2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.