Nicotiana is a genus of about 70 species, mostly native in the Americas, Australia and the Pacific Islands. Few species are economically important: N. tabacum and N. rustica are widely cultivated for the manufacture of tobacco and some are cultivated as ornamentals (Shaw 2000). One species, Nicotiana glauca Graham, is an increasing environmental weed in warm-temperate regions (incl. the Mediterranean area).
Nicotiana is a taxonomically difficult genus, despite the existence of a monograph (Goodspeed 1954). Cultivation and experimental crossings might have blurred species boundaries. Moreover, identification keys are sometimes misleading or even incorrect. Most collections of Nicotiana in Belgian herbaria were wrongly named. Herbarium collections are preferably accompanied by fieldnotes: especially corolla colour should be noted when fresh!
Corollas in Nicotiana are often variously coloured: the colour of the corolla tube differs from that of the corolla lobes and inside and outside of the corolla frequently also have a different colour. Unless otherwise stated corolla colour in the key refers to the inside (i.c. exposed part) of the corolla lobes.
Species of Nicotiana produce high amounts of seeds and rather easily self-sow but they usually are not able to survive western European winters.
1. Entire plant quite glabrous and distinctly glaucous. Corolla yellow. Shrub or small tree === Nicotiana glauca
1. Plant pubescent and often sticky, never glaucous. Corolla variably coloured but rarely yellow. Annual or perennial herbs === 2
2. Stamens inserted at the same level at the base of the corolla tube === 3
2. Stamens inserted at slightly or very different levels at the base or towards the mouth of the corolla tube === 4
3. Corolla greenish-yellow, ca. 10-20 mm long, corolla lobes very short, obtuse or mucronate at apex. Lowermost leaves petiolate, petiole not winged === Nicotiana rustica
3. Corolla pinkish, ca. 30-50 mm long, distinctly lobed, lobes acute at apex. Lowermost leaves shortly petiolate, petiole winged === N. tabacum
4. Inflorescence a dense, compact panicle (flowers nearly whorled). Corolla white, spindle-shaped (widest at middle, narrowed at both ends). Leaves not decurrent. Stamens hairy at base === N. sylvestris
4. Inflorescence a raceme or a loose panicle (flowers not whorled). Corolla white, red, greenish or yellow, narrowly tubular, widest at mouth. Leaves decurrent or not. Stamens glabrous or hairy at base === 5
5. Corolla limb almost entire, green to greenish yellow === N. langsdorffii
5. Corolla limb deeply lobed, variably coloured but usually not greenish yellow === 6
6. Corolla usually red, rarely greenish, whitish or yellow, always smaller. Leaves not or shortly decurrent. Stamens inserted below or above middle of corolla tube === 7
7. Leaves not or only very shortly decurrent. Corolla red, 20-35 mm long. Stamens inserted below middle of corolla tube ===N. forgetiana
Additional aliens: N. longiflora Cav. (S-Am., wool alien) and N. velutina H. Wheeler (Aus., wool alien).
Goodspeed T.H. (1954) The genus Nicotiana. Origins, relationships and evolutions of its species in the light of their distribution, morphologiy and cytogenetics. Waltham, XXI + 536 p.
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.
Sell P. & Murrell G. (2009) Flora of Great Britain and Ireland. Vol. 3 Mimosaceae – Lentibulariaceae. Cambridge University Press, Cambridge: XXVIII + 595 p.
Knapp S., Chase M.W. & Clarkson J.J. (2004). Nomenclature changes and a new sectional classification in Nicotiana (Solanaceae). Taxon 53: 73-82. [available online at: https://www.researchgate.net/publication/233688146_Nomenclatural_Changes...
Shaw J.M.H. (2000) Nicotiana. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 257-261.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Van Ooststroom S.J. & Reichgelt Th.J. (1966) Solanaceae-Orobanchaceae. In: van Ooststroom S.J. & Van der Veen R. a.o. (eds.), Flora Neerlandica, vol. 4(2). KNBV, Amsterdam: 65 p.