Orobanche L.
Molecular studies have shown Orobanche to be non-monophyletic. Two lineages are clearly discernable: on the one hand the Orobanche group that comprises Orobanche sect. Orobanche and the small Near Asian genus Diphelypaea (all with a chromosome base number of x=19) and on the other hand the Phelipanche group that contains Orobanche sects. Gymnocaulis, Myzorrhiza, and Trionychon (with a chromosome base number of x=12) (Schneeweiss & al. 2004). Therefore, the separation of Orobanche in two genera with Phelipanche as a separate genus seems justified. This finding is also supported by pollen aperture type and exine ornamentation. The pollen of Phelipanche is tricolpate, while that of Orobanche is inaperturate (Piwowarczyk & al. 2015). Contemporary floras adopt this modern treatment for Orobanche, e.g. Flora Gallica (Tison & de Foucault 2014) and it is applied here as well.
In its narrowed circumscription Orobanche counts ca. 125-130 species, mostly in the temperate and warm-temperate regions of the northern hemisphere. Eight species are considered native in Belgium (O. alba Steph. ex Willd., O. caryophyllacea Smith, O. elatior Sutton, O. hederae Vaucher ex Duby, O. minor Smith, O. picridis F.W. Schultz, O. rapum-genistae Thuill. and O. teucrii Holandre; see Lambinon & Verloove 2012) but most are rare or even near-extinct.
Orobanche is a difficult genus. Especially herbarium specimens are hard to identify in the absence of photos or supplementary information. Essential for an accurate identification are: colour of corolla and stigma when fresh and host plant.
In addition to Orobanche amethystea Thuill., the only non-native species reliably recorded in Belgium in recent times, a second one should be looked for: O. crenata Forssk. Although declining in many regions (e.g. in France; Tison & de Foucault 2014) it is a weedy species and a parasite on cultivated legumes (mostly on Vicia faba). It has been repeatedly recorded in the British Isles (Stace 2010). Both these species are related and morphologically similar to native O. minor. O. amethystea and the latter are opposed to one another in the following couplet:
1 Filaments inserted ca. 3-6 mm above corolla base. Corolla ca. 15-25 mm (usually ca. 20 mm), whitish or cream suffused with violet. Cauline leaves lanceolate to linear === Orobanche amethystea
Filaments inserted less than 3 mm above corolla base. Corolla smaller (rarely more than 15 mm), rather yellowish, sometimes suffused with violet. Cauline leaves ovate to lanceolate (native) == O. minor
References:
Carlón L, Gómez Casares G, Laínz M, Moreno Moral G, Sánchez Pedraja Ó, Schneeweiss GM. (2008) Más, a propósito de algunas Phelipanche Pomel, Boulardia F.W. Schultz y Orobanche L. (Orobanchaceae) del oeste del Paleártico. Documentos Jard. Bot. Atlántico (Gijón), 6: 1-128. [available online at: http://bibdigital.rjb.csic.es/PDF/Documentos_Jard_Bot_Gijon_6_2008.pdf]
Gevezova M., Dekalska T., Stoyanov K., Hristeva T., Kostov K., Batchvarova R. & Denev I. (2012) Recent advances in Broomrapes research. J. BioSci. Biotech. 1(2): 91-105. [available online at: http://www.jbb.uni-plovdiv.bg/documents/27807/33333/jbb_2012-1%282%29-pa...
Kreutz C.A.J. (1995) Orobanche : Die Sommerwurzarten Europas : ein Bestimmungsbuch = The European broomrape species : A field guide. Vol. 1: Mittel- und Nordeuropa. Stichting Natuurpublicaties Limburg, Den Haag- Maastricht: 159 pp.
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.
Park J., Manen J. & Schneeweiss G. (2007a) Horizontal gene transfer of a plastid gene in the non-photosynthetic flowering plants Orobanche and Phelipanche (Orobanchaceae). Mol. Phylogen. Evol. 43(3): 974-985.
Park J., Schneeweiss G., Weiss-Schneeweiss H. (2007b) Diversity and evolution of Ty1-copia and Ty3-gypsy retroelements in the non-photosynthetic flowering plants Orobanche and Phelipanche (Orobanchaceae). Gene 387(1-2): 75-86. [available online at: https://www.researchgate.net/profile/Hanna_Weiss-Schneeweiss/publication...(Orobanchaceae)/links/02e7e52e8e358d7841000000.pdf]
Piwowarczyk R., Madeja J. & Nobis M. (2015) Pollen morphology of the Central European broomrapes (Orobanchaceae: Orobanche, Phelipanche and Orobanchella) and its taxonomical implications. Plant Systematics and Evolution 301(2): 795-808. [available online at: http://link.springer.com/article/10.1007/s00606-014-1117-6/fulltext.html]
Schneeweiss G.M., Colwell A., Park J.M., Jang C.G. & Stuessy T.F. (2004) Phylogeny of holoparasitic Orobanche (Orobanchaceae) inferred from nuclear ITS sequences. Mol. Phylogenet. Evol. 30(2): 465-478. [available online at: https://www.researchgate.net/publication/8926181_Phylogeny_of_holoparasi...
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Tison J.-M. & de Foucault B. (coord.) (2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.
Van der Land J. (1966) Orobanchaceae. In: Flora Neerlandica, vol. 4(2): 187-205. [available online at: http://natuurtijdschriften.nl/download?type=document&docid=554432]