Verbascum L.
Verbascum is a genus with ca. 360 species in Europe, Asia and Africa (highlands only) (Mabberley 2008). It is still imperfectly known and new species are still regularly described, especially in its center of diversity in Turkey (at present with 243 known species of which 193 are endemic; Yilmaz & Dane 2012). Six species are probably native in Belgium (Lambinon & Verloove 2012), although residence status for some is very controversial: Verbascum lychnitis, V. nigrum and V. thapsus were already present in the 16th century and most likely originally native (Durand 1899). Verbascum densiflorum and V. pulverulentum are known since the 19th century only but at least locally native according to Mosseray (1935-36) although many/most present-day records refer to introduced plants. Perhaps most critical is Verbascum blattaria. It always seems to be confined to man-made, ruderal habitats and was considered to be non-native by Mosseray l.c. (“vraisemblablement introduite et instable”). However, it is now accepted as a native species in western (continental) Europe by most contemporary authors (Hartl 1975b, van der Meijden 2005, Lambinon & Verloove 2012, etc.). At least four additional species are regularly seen as aliens or escapes (see below) but Verbascum may be poorly known in Belgium (compare with, for instance, Sell & Murrell 2009). The genus Verbascum has been critically reviewed in Belgium by Mosseray (1935-36).
Verbascum is rather popular in horticulture. At least 23 species are cultivated as ornamentals in Europe (Cullen 2000, Jäger & al. 2008). Some are much reminiscent of the species treated in this account and may have been overlooked so far (Verbascum bombyciferum Boiss., V. longifolium Ten., V. olympicum Boiss., V. pyramidatum Bieb., etc.).
Where-ever two or more species grow together hybrids occur. These always have reduced pollen and are usually highly sterile (Murbeck 1933). Several of these hybrids have been recorded in Belgium but they are poorly known and add to the confusion. For instance, some hybrids of Verbascum nigrum and V. thapsus (or V. densiflorum) are remarkably reminiscent of V. chaixii (especially subsp. austriacum): distinctly petiolate, glabrescent lower leaves, branched inflorescence, filaments with mostly purplish hairs, etc. In Belgium both these hybrids (especially V. xambiguum Lejeune, the hybrid of V. densiflorum and V. nigrum) are not rare at all and potentially grow where-ever both parent species grow in close proximity.
Additional useful information on the genus Verbascum (incl. photos, scans of herbarium specimens, descriptions, etc.) is provided by https://verbascum.org.
1 Corolla violet to purple === Verbascum phoeniceum
Corolla yellow or whitish === 2
2 Anthers all identical: symmetrical and reniform === 3
Anthers of two kind: upper three symmetrical and reniform, lower two markedly asymmetrical, placed transversely on the filaments === 6
3 Filament hairs violet === 4
Filament hairs white or yellowish === 5
4 Lower leaves cordate at base. Inflorescence usually unbranched (sometimes branched). Pedicels very unequal, up to 15 mm long, some much longer than calyx. Petals glandular punctate (native) === V. nigrum
Lower leaves truncate to rounded at base. Inflorescence branched. Pedicels less unequal, at most 6 mm long and only slightly longer than calyx. Petals eglandular === V. chaixii
5 Leaves densely and persistently tomentose on both sides === V. speciosum
Leaves becoming sparsely tomentose to nearly glabrous, at least above (native) === V. lychnitis and V. pulverulentum
6 Filament hairs violet === 7
Filament hairs white or yellowish === 8
7 Flowers solitary. Pedicels up to 14 mm long at maturity, longer than calyx. Stem glandular hairy in upper part only. Flowers subtended by a bract, without bracteoles (native) === V. blattaria
Flowers 1-5. Pedicels 2-5(-7) mm long at maturity, at most as long as calyx. Stem often more or less glandular throughout. Flowers subtended by bracts and bracteoles === V. virgatum
8 Upper cauline leaves distinctly decurrent (native) === V. densiflorum and V. thapsus
Upper cauline leaves not or scarcely decurrent === V. phlomoides
Additional aliens: Verbascum banaticum Schrad. (SE-Eur., wool alien) and V. sinuatum L. (Medit., wool and grain alien).
Literature:
Al Hemaid F.M.A. (2002) Taxonomic revision of the genus Verbascum L. (Scrophulariaceae) from Saudi Arabia. Bangladesh J. Pl. Taxon. 9(1): 1-13.
Arts-Damler T. (1960) Cytogenetical studies on six Verbascum species and their hybrids. Genetica 31: 241-328.
Benedí C., Orell J. & Orell Jaquatot J.J. (1989) Notes taxonomiques nomenclaturals i corologiques de les especies Verbascum L. (Scrophulariaceae) a Mallorca. Butll. Inst. Catalana Hist. Nat. 57: 61-64.
Cullen J. (2000) Verbascum. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 283-287.
Domin K. (1935) Generis Verbasci L. specierum et hybridarum in Čechoslovakia sponte crescentium enumeration. Vĕst. Král. Čes. Spol. Nauk. Tr. 2: 1-22.
Durand T. (1899) Phanérogames. In: De Wildeman E. & Durand T., Prodrome de la flore belge. A. Castaigne Editeur, Bruxelles: 1112 p.
Easy G.M.S. (1998) Verbascum hybrids. In: Rich T.C.G. & Jermy A.C. (eds.), Plant crib: 255-257. BSBI, London.
Easy G. (2006) Cambridgeshire Verbascums. Nat. Cambridge 48: 16-19.
Ferguson I.K. (1972) Verbascum. In: Tutin T.G. & al.(eds;), Flora Europaea, vol. 3. Cambridge University Press: 205-216.
Franchet A. (1868) Essai sur les espèces du genre Verbascum croissant spontanément dans le centre de la France, et plus particulièrement sur leurs hybrides. Angers, P. Lachèse, Belleuvre et Dolbeau: 205 p.
Franchet M.A. (1875) Études sur les Verbascum de la France et de l'Europe centrale. Lemercier et fils, Vendôme: 131 p.
Grabias B., Świątek L. & Świętosławski J. (1992) The morphology of hairs in Verbascum L. species. Acta Soc. Bot. Pol. 60(3-4): 191-208. [available online at: https://pbsociety.org.pl/journals/index.php/asbp/issue/view/83]
Hartl D. (1975b) Verbascum. In: Hegi G. (ed.), Illustrierte Flora van Mitteleuropa, vol. 6(1) (2nd ed.). Paul Parey Verlag, Berlin & Hamburg: 37-62.
Huber-Morath A. (1971) Die Türkischen Verbasceen. Denkschr. Schweiz. Naturf. Ges. 87: 1-166.
Huber-Morath A. (1973) Verbascum L. s.l. (incl. Celsia L. et Staurophragma Fisch et Mey.). Bauhinia 5(1): 7-16.
Huber-Morath A. (1978) Verbascum. In: Davis P.H. (ed.), Flora of Turkey and the East Aegean Islands, vol. 6. Edinburgh Univ. Press, Edinburgh: 461-603.
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.
Juan R., Fernandez I. & Pastor J. (1997) Systematic consideration of microcharacters of fruits and seeds in the genus Verbascum (Scrophulariaceae). Ann. Bot. (Rome) 80: 591-598. [available online at: http://aob.oxfordjournals.org/content/80/5/591.full.pdf]
Karaveliogullari F. A. & Aytaç Z. (2008) Revision of the genus Verbascum L. (Group A) in Turkey. Bot. Res. J. 1: 9-32. [available online at: http://docsdrive.com/pdfs/medwelljournals/brj/2008/9-32.pdf]
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.
Lebeau J. (1991) Réflexions sur les formes a fleurs blanches dans le genre Verbascum. Nat. Mosana 44(2): 36-38.
Lobin W. & Porembski S. (1994) The genus Verbascum (Scrophulariaceae) on the Cape Verde Islands, W. Africa. Willdenowia 24(1-2): 65-81.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Milberg P. (1990) Hur länge kan ett frö leva? Svensk Botanisk Tidskrift 84: 323-352.
Mosseray R. (1935-36), Matériaux pour une flore de Belgique. IV. Le genre Verbascum. Bull. Soc. Roy. Bot. Belg. 68: 88-103.
Murbeck S. (1933) Monographie der Gattung Verbascum. Acta Univ. Lund 29: 1-630.
Murbeck S. (1936) Nachträge zur Monographie der Gattung Verbascum. Acta Univ. Lund 32: 1-46.
Murbeck S. (1939) Weitere Studien über die Gattungen Verbascum und Celsia. Acta Univ. Lund 35: 1-71.
Pugsley H.C. (1957) Verbascums in the garden. Journal of the Royal Horticultural Society 82: 489-491
Schrader H.A. (1813) Monographia Generis Verbasci. Sectio 1: 40 p.
Schrader H.A. (1823) Monographia Generis Verbasci. Sectio 2: 57 p.
Sell P. & Murrell G. (2009) Flora of Great Britain and Ireland. Vol. 3 Mimosaceae – Lentibulariaceae. Cambridge University Press, Cambridge: XXVIII + 595 p.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Van der Meijden R. (2005) Heukels’ Flora van Nederland (23e druk). Wolters-Noordhoff, Groningen: 685 p.
Yilmaz G. & Dane F. (2012) The genus Verbascum L. in European Turkey. Bot. Serbica 36(1): 9-13. [available online at: http://academicpublishingplatforms.com/downloads/pdfs/bs/volume1/201204081916_Th_e_genus_Verbascum_L._%C4%B1n_European_Turkey.pdf]