Allium

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Allium
Allium flavum
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Amaryllidaceae
Subfamily: Allioideae
Tribe: Allieae
Genus: Allium
L.
Type species
Allium sativum
Species

See text

Allium is a monocot genus of flowering plants, informally referred to as the onion genus. The generic name Allium is the Latin word for garlic.[1]

The genus contains hundreds of distinct species; many have been harvested through human history, but only about a dozen are still economically important today as crops or garden vegetables. Many others are cultivated as ornamental plants.

Allium is taxonomically difficult and species boundaries are unclear. Most authorities accept about 750 species.[2] Estimates of the number of species have been as low as 260,[3] and as high as 860.[4] The type species for the genus is Allium sativum.[5]

Allium species occur in temperate climates of the northern hemisphere, except for a few species occurring in Chile (such as A. juncifolium), Brazil (A. sellovianum) or tropical Africa (A. spathaceum). They can vary in height between 5 cm and 150 cm. The flowers form an umbel at the top of a leafless stalk. The bulbs vary in size between species, from very small (around 2–3 mm in diameter) to rather large (8–10 cm). Some species (such as Welsh onion, A. fistulosum) develop thickened leaf-bases rather than forming bulbs as such. Allium is a genus of perennial bulbous plants that produce chemical compounds (mostly cysteine sulfoxide) that give them a characteristic onion or garlic taste and odor. Many are used as food plants, though not all members of the genus are equally flavorful. In most cases, both bulb and leaves are edible. Their taste may be strong or weaker, depending on the species.

In the APG III classification system, Allium is placed in the family Amaryllidaceae, subfamily Allioideae (formerly the family Alliaceae).[6] In some of the older classification systems, Allium was placed in Liliaceae.[7][8][9][10][11] Molecular phylogenetic studies have shown that this circumscription of Liliaceae is not monophyletic.

Allium is one of about 57 genera of flowering plants that have more than 500 species.[12] It is by far the largest genus in the Amaryllidaceae, and also in the Alliaceae in classification systems in which that family is recognized as separate.[3]

Description

Allium species are herbaceous perennials with flowers produced on scapes. They grow from solitary or clustered tunicate bulbs and many have an onion odor and taste. Plants are perennialized by bulbs that reform annually from the base of the old bulb, or are produced on the ends of rhizomes or, in a few species, at the ends of stolons. A small number of species have tuberous roots. The bulbs have outer coats that are commonly brown or grey, with a smooth texture, and are fibrous, or with cellular reticulation. The inner coats of the bulbs are membranous.

Many alliums have basal leaves that commonly wither away from the tips downward before or while the plant flower, but some species have persistent foliage. Plants produce from one to twelve leaves, most species having linear, channeled or flat leaf blades. The leaf blades are straight or variously coiled, but some species have broad leaves, including A. victorialis and A. tricoccum. The leaves are sessile, and very rarely narrowed into a petiole.

The terete or flattened flowering scapes are normally persistent. The inflorescences are umbels, in which the outside flowers bloom first and flowering progresses to the inside. Some species produce bulbils within the umbels, and in some species the bulbils replace some or all the flowers. The umbels are subtended by noticeable spathe bracts, which are commonly fused and normally have around 3 veins.

The flowers are erect or in some species pendent, having six petal-like tepals produced in two whorls. The flowers have one style and six epipetalous stamens; the anthers and pollen can vary in color depending on the species. The ovaries are superior, and three-lobed with three locules.

The fruits are capsules that open longitudinally along the capsule wall between the partitions of the locule.[13][14] The seeds are black, and have a rounded shape.

Some bulbous alliums increase by forming little bulbs or "offsets" around the old one, as well as by seed. Several species can form many bulbils in the flowerhead; in the so-called "tree onion" or Egyptian onion (A. × proliferum) the bulbils are few, but large enough to be pickled.

Taxonomy

The taxonomy of Allium is poorly understood, with incorrect descriptions being widespread. Allium spicatum has been treated by many authors as Milula spicata, the only species in the monospecific genus Milula. In 2000, it was shown to be embedded in Allium.[15]

In 2006, a phylogeny of Allium was published based on the nuclear ribosomal gene ITS. The authors of this study divided Allium into 15 subgenera and 72 sections.[16] They defined the subgenus Rhizirideum in a much narrower sense than in previous classifications.

Subsequent molecular phylogenetic studies have shown that the 2006 classification is a considerable improvement over previous classifications, but some of its subgenera and sections are probably not monophyletic. One of these studies focused on the subgenus Amerallium which is strongly supported as monophyletic.[17] Another study focused on Allium ampeloprasum and its relatives within the section Allium of subgenus Allium.[2] Sampling in this study was not sufficient to test the monophyly of section Allium.

Habitat

The majority of Allium species are native to the Northern Hemisphere, mainly in Asia. A few species are native to Africa and Central and South America.[13] Species grow in various conditions from dry, well-drained mineral-based soils to moist, organic soils; most grow in sunny locations but a number also grow in forests, or even in swamps / water.

Cultivation

Many Allium species have been harvested through human history, but only about a dozen are still economically important today as crops or garden vegetables.[18] These include onions (A. cepa), French shallots (A. oschaninii), leeks (A. ampeloprasum), scallions (various Allium species), and herbs such as garlic (A. sativum) and chives (A. schoenoprasum). Others are cultivated as ornamentals.[19]

Ornamental

Selection of cultivated Alliums displayed at the BBC Gardeners' World show in June 2011.

Some Allium species, including A. cristophii and A. giganteum, are used as border plants for their ornamental flowers, and their "architectural" qualities.[20] Several hybrids have been bred, or selected, with rich purple flowers. A. hollandicum 'Purple Sensation' is one of the most popular and has been given an Award of Garden Merit (H4).[21] These ornamental onions come in a wide variety of sizes and colours, ranging from white (Allium 'Mont Blanc'), blue (A. caeruleum), to yellow (A. flavum) and purple (A. giganteum). By contrast, other species (such as invasive A. triquetrum and A. ursinum) can become troublesome garden weeds.[20][22]

Ecology

Various Allium species are used as food plants by the larvae of some Lepidoptera including Cabbage Moth, common swift moth (recorded on garlic), Garden Dart moth, Large Yellow Underwing moth, Nutmeg moth, Setaceous Hebrew Character moth, Turnip Moth and Schinia rosea, a moth that feeds exclusively on Allium species.

Dogs and cats are very susceptible to poisoning after the consumption of certain[clarification needed] species.[23]

Species

See List of Allium species for a full list. Some important species include:

Notes

  1. ^ Umberto Quattrocchi. 2000. CRC World Dictionary of Plant Names volume I, page 91. CRC Press: Boca Raton; New York; Washington,DC;, USA. London, UK. ISBN 978-0-8493-2673-8 (set).
  2. ^ a b Pablo Hirschegger, Jernej Jaške, Peter Trontelj, and Borut Bohanec. 2010. "Origins of Allium ampeloprasum horticultural groups and a molecular phylogeny of the section Allium (Allium; Alliaceae)". Molecular Phylogenetics and Evolution 54(2):488-497. doi:10.1016/j.ympev.2009.08.030
  3. ^ a b Knud Rahn. 1998. "Alliaceae" pages 70-78. In: Klaus Kubitzki (editor). The Families and Genera of Vascular Plants volume III. Springer-Verlag: Berlin;Heidelberg, Germany. ISBN 978-3-540-64060-8
  4. ^ World Checklist of Selected Plant Families. (see External links below).
  5. ^ Allium In: Index Nominum Genericorum. In: Regnum Vegetabile (see External links below).
  6. ^ Chase, M.W.; Reveal, J.L.; Fay, M.F. (2009), "A subfamilial classification for the expanded asparagalean families Amaryllidaceae, Asparagaceae and Xanthorrhoeaceae", Botanical Journal of the Linnean Society, 161 (2): 132–136, doi:10.1111/j.1095-8339.2009.00999.x {{citation}}: Unknown parameter |lastauthoramp= ignored (|name-list-style= suggested) (help)
  7. ^ Eric Block, "Garlic and Other Alliums: The Lore and the Science" (Cambridge: Royal Society of Chemistry, 2010)
  8. ^ James L. Brewster, "Onions and Other Alliums" (Wallingford: CABI Publishing, 2008)
  9. ^ Dilys Davies, "Alliums: The Ornamental Onions" (Portland: Timber Press, 1992)
  10. ^ Haim D. Rabinowitch, Leslie Currah, "Allium Crop Sciences: Recent Advances" (Wallingford: CABI Publishing, 2002)
  11. ^ Penny Woodward, "Garlic and Friends: The History, Growth and Use of Edible Alliums" (South Melbourne: Hyland House, 1996)
  12. ^ David G. Frodin. 2004. "History and concepts of big plant genera" Taxon 53(3):753-776.
  13. ^ a b http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=101086
  14. ^ http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=101086
  15. ^ Nikolai Friesen, Reinhard M. Fritsch, Sven Pollner and Frank R. Blattner. 2000. "Molecular and Morphological Evidence for an Origin of the Aberrant Genus Milula within Himalayan Species of Allium (Alliacae)". Molecular Phylogenetics and Evolution 17(2):209-218. doi:10.1006/mpev.2000.0844
  16. ^ Nikolai Friesen, Reinhard M. Fritsch, and Frank R. Blattner. 2006. "Phylogeny and new intrageneric classification of Allium (Alliaceae) based on nuclear ribosomal DNA ITS sequences". Aliso 22(Monocots: Comparative Biology and Evolution):372-395.
  17. ^ Nhu H. Nguyen, Heather E. Driscoll, and Chelsea D. Specht. 2008. "A molecular phylogeny of the wild onions (Allium; Alliaceae) with a focus on the western North American center of diversity". Molecular Phylogenetics and Evolution 47(3):1157-1172. doi:10.1016/j.ympev.2007.12.006
  18. ^ Gualtiero Simonetti (1990). Stanley Schuler (ed.). Simon & Schuster's Guide to Herbs and Spices. Simon & Schuster, Inc. ISBN 0-671-73489-X.
  19. ^ Anthony Huxley, Mark Griffiths, and Margot Levy (1992). The New Royal Horticultural Society Dictionary of Gardening. The Macmillan Press,Limited: London. The Stockton Press: New York. ISBN 978-0-333-47494-5 (set).
  20. ^ a b Brickell, Christopher (Editor-in-chief),The Royal Horticultural Society A–Z Encyclopedia of Garden Plants, p.95, Dorling Kindersley, London, 1996, ISBN 0-7513-0303-8
  21. ^ RHS Plant Finder 2009–2010, p68, Dorling Kindersley, London, 2009, ISBN 978-1-4053-4176-9
  22. ^ Lloyd, Christopher & Rice, Graham, (1991) Garden Flowers From Seed, p45, Viking, ISBN 0-670-82455-0
  23. ^ http://veterinarymedicine.dvm360.com/vetmed/Medicine/Toxicology-Brief-iAlliumi-species-poisoning-in-dog/ArticleStandard/Article/detail/174478

References

External links

Wikimedia Commons has media related to Allium.
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