Primula L.
Primula is a large genus that counts ca. 500 species that are nearly exclusively distributed in the northern hemisphere (Mabberley 2008), with a few additional species in northeastern Africa, southeastern Asia and South America. It is by far most diverse in western China and the Himalayas where more than 300 species are found (Hu & Kelso 1996). Only three species are native in Belgium: Primula elatior (L.) Hill, P. veris L. and P. vulgaris Huds. (Lambinon & Verloove 2012).
The genus Primula is exceedingly popular in horticulture and, as a result of hybridization and selection, species limits are blurred in several groups. Richards & Richardson (1997) cite 127 species and numerous infraspecific taxa and cultivars that are cultivated as ornamentals in Europe (see also Jäger & al. 2008). Both these references provide numerous additional literature sources. The genus being of a lesser importance in the wild in Belgium (as escapes) these are not repeated here.
Up to present only two cultivated species have been reliably recorded in the wild in Belgium, Primula denticulata J.E. Smith and P. florindae Kingdon-Ward.Some others, however, may have been overlooked (see Stace 2010 for an interesting overview of species that are susceptible to being encountered in the wild in western Europe). All native species, as well as cultivars of some of them, are also widely cultivated and sometimes occur in areas where they are not originally native. Especially forms of Primula vulgaris with non-yellow corollas are much grown and are regularly found in the wild (see photo).
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Useful additional information on the genus in cultivation is available at the American Primrose Society at http://www.americanprimrosesociety.org/.
1 Inflorescence with mealy coating (at least when young), without multicellular hairs. Leaves usually deciduous === 2
Mealy coating absent, plant with multicellular hairs. Leaves usually persistent (native) === P. elatior, P. veris and P. vulgaris
2 Leaves with distinct stalk up to 40 cm long, truncate to cordate at base. Flowers borne in a loose head, yellow === Primula florindae
Leaves with indistinct stalk. Flowers borne in a tight head, sessile or nearly so, lilac to lavender (or variously coloured in cultivars but never yellow) === P. denticulata
Literature:
Cain R.B. (1967) The genus Primula, a review of its diversity and origin. Bull. Alpine Gard. Soc. Gr. Brit. 35: 128-171.
Fenderson G.K. (1986) A Synoptic Guide to the Genus Primula: 213 p.
Hu C.M. & Kelso S. (1996) Primulaceae. In: Wu Z.Y. & Raven P.H. (eds.), Flora of China, vol. 15. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis: 99-185. [available online at: http://flora.huh.harvard.edu/china/mss/volume15/Primulaceae.published.pdf]
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.
Kovtonyuk N.K. & Goncharov A.A. (2009) Phylogenetic relationships in the genus Primula L. (Primulaceae) inferred from the ITS region sequences of nuclear rDNA. Russian Journal of Genetics 45(6): 663-670.
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.
Mast A.R., Kelso Y. & Conti E. (2006) Are any primroses (Primula) primitively monomorphic? New Phytologist 171: 605-616. [available online at: https://www.researchgate.net/publication/6919254_Are_any_primroses_%28Primula%29_primitively_monomorphic]
Mast A.R., Kelso Y., Richards A.J., Lang D.J., Feller D.M.S. & Conti E. (2001) Phylogenetic relationships in Primula L. and related genera (Primulaceae) based on noncoding chloroplast DNA. International Journal of Plant Sciences 162: 1381-1400. [available online at: http://www.systbot.uzh.ch/static/personen/elena_conti_assets/Primula_IJPS.pdf]
Pax F. (1889) Monographische übersicht über die Arten der Gattung Primula. Botanische Jahrbücher 10: 75-241.
Richards A.J. (2002) Primula. 2nd edition. B.T. Batsford Ltd., London: 346 p.
Richards A.J. & Richardson J.E. (1997) Primula. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 511-535.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Trift I., Källersjö M. & Anderberg A.A. (2002) The monophyly of Primula (Primulaceae) evaluated by analysis of sequences from the chloroplast gene rbcL. Systematic Botany 27: 396-407.