Allium L.

Allium is, in its traditional circumscription, a large genus of ca. 700 (or even more than 850; Deniz & al. 2015) species, widely distributed in the northern hemisphere. It is best represented in China where about one sixth of all known species occur, many endemic (Xu & Kamelin 2000). Some recent authors have – based on molecular studies – raised subgenera to generic rank (Banfi & al. 2011), e.g. Caloscordum Herb. (with, among others, C. cristophii (Trautv.) Banfi & Galasso and C. nigrum (L.) Banfi & Galasso) and Nectaroscordum Lindl. (with e.g. N. pendulinum (Ten.) Galasso & Banfi, N. roseum (L.) Galasso & Banfi, N. triquetrum (L.) Galasso & Banfi and native N. ursinum (L.) Galasso & Banfi) but subsequently this viewpoint was not followed by other authors (compare also with Euro+Med Plantbase account for Allium at, Tison & de Foucault 2014, etc.).
Four species are native in Belgium as well: Allium oleraceum L., A. sphaerocephalon L., A. ursinum L. and A. vineale L. (Lambinon & Verloove 2012). Most of these are also cultivated in gardens and often occur in places where they are not native. The American Allium tricoccum Ait. Is grown as an ornamental (Stearn 1986; note, however, that it is not listed by Fritsch 2015) and much looks like A. ursinum; it might have passed unrecorded. It has shorter perianths (4-5 mm vs. 9-12 mm) with stamens about equaling the perianth (stamens about ½ the length of the perianth in A. ursinum) (Moore 1954).
Several species of the genus Allium are important vegetables and are widely cultivated in agricultural fields and in gardens. They are, however, remarkably scarce on dumps (or not seen at all). Most likely to be encountered are Allium cepa L. (onion; incl. A. salota Dostál) and Allium porrum L. (leek) (see for instance Lebeau 1954). Less frequently cultivated (or on a much smaller scale) are Allium fistulosum L. and Allium sativum L. and possibly others (see for instance Stace 2010 for a more detailed account).
In addition to the ornamental species treated below, several others might occur on dumps or near gardens. Some of the more regular ones are keyed-out by Stace (2010) or Van der Meijden (2005). Stearn (1986) provides a key for 96 cultivated taxa of Allium. A comprehensive checklist with ca. 250 species of Allium known to be offered for sale in the horticultural trade is presented by Fritsch (2015). Further useful information on the genus Allium is provided by the Pacific Bulb Society at:
The cultivated and escaped taxa of Allium in Belgium are probably insufficiently known. The present account therefore is a preliminary and (probably) incomplete one.

1 Leaves contracted at base into a stalk, the blade (narrowly) elliptic, 20-70 mm wide (native) === Allium ursinum
Leaves not stalked, linear to filiform or, if wider, then not contracted into distinct stalk === 2

2 Stem triquetrous in cross section. Petals always white. Stigma 3-lobed === 3
Stem circular in cross section. Petals white, greenish, pink or purplish. Stigma entire === 5

3 Leaf single, up to 25 mm wide. Inflorescence composed of flowers and bulbils or of bulbils only. Tepals with very narrow and faint green line === A. paradoxum
Leaves (1-)2-5, 4-12 mm wide. Inflorescence composed of flowers only. Tepals with strong green line === 4

4 Flowers star-shaped, with petals clearly spreading, 3-5 mm long. Inflorescence with erect and pendent flowers at beginning of flowering, the longest pedicels up to 40 mm long. Stem usually not exceeding 25 cm === A. pendulinum
Flowers campanulate, with petals 10-18 mm long. Inflorescence with all flowers pendent from beginning of flowering, on much shorter pedicels. Stem up to 45 cm long === A. triquetrum

5 Spathes 2, persistent, attenuate at apex (apical part much longer than basal part and spathe much exceeding the inflorescence) === 6
Spathe 1, 2 or more, deciduous or more rarely persistent (apical part not much longer than basal part and spathe shorter to slightly longer than the inflorescence) === 7

6 Leaves circular, usually hollow. Anthers slightly shorter to slightly longer than tepals. Tepals pinkish-, greenish- or brownish white (native) === A. oleraceum
Leaves plane, bifacial, solid. Anthers much longer than tepals. Tepals bright pink === A. carinatum

7 Three lowermost filaments tricuspidate at apex === 8
All filaments simple === 10

8 Leaves circular, hollow (native) === A. vineale and A. sphaerocephalum
Leaves plane, bifacial, solid === 9

9 Stamens longer than petals === A. porrum
Stamens shorter than petals === A. scorodoprasum

10 Inflorescence consisting entirely of bulbils. Leaves and stems inflated === A. cepa p.p.
Inflorescence consisting of flowers and bulbils or consisting of flowers only === 11

11 Leaves with stiff spreading hairs beneath and on margins === A. cristophii
Leaves glabrous === 12

12 Stem and leaves inflated, hollow === A. cepa p.p.
Stem and leaves not inflated, solid === 13

13 Leaves 20-80 mm wide === 14
Leaves up to 15 mm wide === 16

14 Stamens clearly longer than tepals === A. macleanii
Stamens up to as long as tepals === 15

15 Ovary stalked (remove perianth and stamens). Perianth violet === A. hollandicum (A. aflatunense auct.)
Ovary sessile. Perianth white === A. nigrum

16 Leaves cylindric, hollow. Tepals lilac to purple === A. schoenoprasum
Leaves flat, solid. Tepals white to pink === 17

17 Perianth cup or bell-shaped, pink (sometimes very pale, nearly white) === A. roseum
Perianth star-shaped, white === A. ramosum (incl. A. tuberosum)

Additional aliens: Allium fistulosum L. (E-As., garden escape) and A. moly L. (SW-Eur., garden escape).


There is a vast literature on onions. Only a small selection is presented here under.

Banfi E., Galasso G. & Soldano A. (2011) Notes on systematics and taxonomy for the Italian vascular flora. 2. Atti Soc. it. Sci. nat. Museo civ. Stor. nat. Milano 152 (II): 85-106. [available online at:]

Brewster J.L. (2008) Onions and Other Alliums. Wallingford: CABI Publishing.

Davies D. (1992) Alliums. The Ornamental Onions: 168 pp.

Deniz I.G., Genç İ. & Sarı D. (2015) Morphological and molecular data reveal a new species of Allium (Amaryllidaceae) from SW Anatolia, Turkey. Phytotaxa 212(4): 283-292.

Friesen N., Fritsch R. & Bachmann K. (1997) Hybrid origin of some ornamentals of Allium subgenus Melanocrommyum verified with GISH and RAPD. Theoretical and Applied Genetics 95: 1229-1238. [available online at:]

Friesen N., Fritsch R.M. & Blattner F.R. (2006) Phylogeny and new classification of Allium (Alliaceae) based on nuclear ribosomal DNA ITS sequence. Aliso 22: 372-395. [available online at:

Fritsch R.M. (2012) Illustrated key to the sections and subsections and brief general circumscription of Allium subg. Melanocrommyum. Phyton 52(1): 1-37. [available online at:

Fritsch R.M. (2015) Checklist of ornamental Allium species and cultivars currently offered in the trade. Publication in the Internet at:

Fritsch R.M. (2016) A Preliminary Review of Allium subg. Melanocrommyum in Central Asia. Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung Gatersleben (IPK): 288 pp. [available online at:

Fritsch R.M. & Abbasi M. (2013) A taxonomic review of Allium subg. Melanocrommyum in Iran. Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung Gatersleben: 240 pp. [available online at:

Fritsch R.M., Blattner F.R. & Gurushidze M. (2010) New classification of Allium L. subg. Melanocrommyum (Webb & Berthel.) Rouy (Alliaceae) based on molecular and morphological characters. Phyton 49: 145-320. [available online at:

Fritsch R.M. & Gurushidze M. (2009)  Phylogenetic relationships of ornamental species in Allium L. subg. Melanocrommyum (Webb et Berthel.) Rouy (Alliaceae). Israel Journal of Plant Sciences 57(4): 287-295. [available online at:

Gurushidze M., Fritsch R.M. & Blattner F.R. (2008) Phylogenetic analysis of Allium subg. Melanocrommyum infers cryptic species and demands a new sectional classification. Molecular Phylogenetics and Evolution 49(3): 997-1007. [available online at:

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.

Khassanov F.O., Yengalycheva S.S. & Japakova U.N. (1997) Taxonomic remarks on Allium sect. Allium s. lat. Bot. Jahrb. Syst. 119(2): 267-275. [available online at:

Kollman F. (1993) The genus Allium in the Middle East., Proceedings of the Fifth Optima Meeting. Optima 5: 91-107.

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. (1954) Plantes trouvées en 1952 et 1953 au terrain d’immondices de la Ville de Charleroi à Jamioulx, au cours d’une cinquantaine de promenades. Nat. Mosana 6: 59-61.

Mathew B. (1996) A Review of Allium section Allium: ix + 176 pp.

McNeal Jr. D.W. & Jacobsen T.D. (2002) Allium. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 26. Oxford University Press, New York-Oxford: 39-40. [available online at:]

Moore H.E. Jr. (1954) The cultivated Alliums. I. The broad-leaved onions. Baileya 2: 103-113.

Moore H.E. Jr. (1954) The cultivated Alliums. II. Baileya 2: 117-123.

Moore H.E. Jr. (1955) The cultivated Alliums. III. Baileya 3: 137-149.

Moore H.E. Jr. (1955) The cultivated Alliums. IV. Baileya 3: 156-167.

Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.

Stearn W.T. (1978) European species of Allium and allied genera of Alliaceae: a synonymic enumeration. Ann. Mus. Goulandris 4: 83-198.

Stearn W.T. (1981) The genus Allium in the Balkan peninsula. Bot. Jahrb. Syst. 102: 201-213.

Stearn W.T. (1986) Allium. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 1: 233-246. Cambridge University Press, Cambridge.

Stearn W.T. (1992) How many species of Allium are known? Kew Mag. 9: 180-182.

Tison J.-M. & de Foucault B. (coord.) 2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.

Van der Meijden R. (2005) Heukels’ Flora van Nederland (23e druk). Wolters-Noordhoff, Groningen: 685 p.

Vvedenskii A.I. (1935) Allium. In: Komarov V.A. (ed.), Flora U.S.S.R., vol. 4: 112–280. Botanical Institute of Academy of Science, Leningrad. [available online at:]

Xu J-M. & Kamelin R.V. (2000) Allium. In: Wu Z.Y. & Raven P.H. (eds.), Flora of China, vol. 24: 165–202. Science Press and Missouri Botanical Garden Press, Beijing and St. Louis. [available online at:]

Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith