Allium

Allium

Alliums
Genus:	Allium
Family:	Lilaceae
Weediness:	Most species can be weedy if allowed to go to seed
Pollination:	Insects

Allium is the genus which includes both Onions and Garlics, with about 1250 species, making it one of the largest plant genera in the world. They are perennial bulbous plants that produce chemical compounds that give them a characteristic onion or garlic taste and odor, and many are used as food plants. Allium is classified in family Alliaceae although some classifications have included it in the lily family (Liliaceae).

Members of the genus include many valued vegetables such as onions, shallots, leeks and herbs such as garlic and chives. A strong "oniony" odor is characteristic of the whole genus, but not all members are equally flavorful.

Description

Allium species occur in temperate climates of the northern hemisphere, except for a few species occurring in Chile (as Allium juncifolium), Brazil (Allium sellovianum) or tropical Africa (Allium 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 big (8–10 cm). Some species (such as Welsh onion, A. fistulosum) develop thickened leaf-bases rather than forming bulbs as such.

Most bulbous alliums increase by forming little bulbs or "offsets" around the old one, as well as by seed. Several species can form many bulbils (tiny bulbs) in the flowerhead; in the so-called "tree onion" (A. cepa Proliferum Group) the bulbils are few, but large enough to be used for pickling.

Species

Some important species:
Allium acuminatum - tapertip onion
Allium ampeloprasum

A. a. var. ampeloprasum - elephant garlic

A. a. var. kurrat - kurrat

A. a. var. porrum - leek (vegetable)|leek

Allium anceps - twinleaf onion
Allium angulosum - mouse garlic
Allium atrorubens - dark red onion
Allium campanulatum - dusky onion
Allium canadense - Canadian garlic
Allium cepa - garden onion
Allium fistulosum - Welsh onion
Allium neapolitanum - white garlic
Allium nevii - Nevius' garlic
Allium nigrum - black garlic
Allium oleraceum - field garlic
Allium oschaninii - shallot
Allium ramosum - wild Chinese chives
Allium sativum - cultivated garlic
Allium schoenoprasum - chives
Allium scorodoprasum - Sand leek Allium triquetrum - three-cornered leek, triquetous garlic
Allium tuberosum - Chinese chives
Allium ursinum - wild garlic, ramsons
Allium vineale - crow garlic
See full list.

Uses

Some Allium species, including A. cristophii and A. giganteum, are used as border plants for their flowers, and their "architectural" qualities. Several hybrids have been bred, or selected, with rich purple flowers. Allium hollandicum 'Purple Sensation' is one of the most popular and has been given an Award of Garden Merit (H4). By contrast, other species (such as the invasive Allium triquetrum) can become troublesome garden weeds.

Pests and diseases

Leaf Spots

Downy Mildew

Southern Blight

Bulb Rots

• Onion White Rot: Sclerotinium cepivorum
• Onion Neck Rot: Botrytis alii

Rusts

Smuts

Nematodes

• Onion Nematode

Aphids

• Shallot Aphid: Myzus ascalonicus

Thrips

• Tobacco Thrips: Frankliniella fusca
• Western Flower Thrips: Frankliniella occidentalis
• Onion Thrips: Thrips tabaci

Flies

• American Serpentine Leafminer: Liriomyza trifolii
• Onion Bulb Fly: Emerus strigatus
• Onion Maggot: Delia antiqua
• Pea Leafminer: Liriomyza huidobrensis
• Seedcorn Maggot: Delia platura

Beetles

• Banded Cucumber Beetle: Diabrotica balteata

Caterpillars

• Beet Armyworm: Spodoptera exigua
• Saltmarsh Caterpillar: Estigmene acrea

Mites

• Bulb Mite: Rhizoglyphus echinopus

w:Cabbage Moth, Common Swift moth (recorded on garlic), w:Garden Dart moth, w:Large Yellow Underwing moth, Nutmeg moth, w:Setaceous Hebrew Character moth, w:Turnip Moth and Schinia rosea, a moth which feeds exclusively on Allium spp.

References

• Ann Fowler Rhoads and Timothy A. Block (2000). The Plants of Pennsylvania: An Illustrated Manual. Anna Anisko, illustrator. Morris Arboretum, University of Pennsylvania Press. pp. 858–859.
• Christopher Brickell and Judith D. Zuk (1997). The American Horticultural Society A-Z Encyclopedia of Garden Plants. DK Publishing. pp. 95–98.
• Staff of the L. H. Bailey Hortorium (1976). Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada. Cornell University Press. pp. 47–54.
• Pirone, Pascal P. (1978). Diseases & Pests of Ornamental Plants (Fifth Edition ed.). John Wiley & Sons, New York. p. 125. {{cite book}}: |edition= has extra text (help)
• Cranshaw, Whitney (2004). Garden Insects of North America: The Ultimate Guide to Backyard Bugs. Princeton University Press. p. 579.
• Pippa Greenwood, Andrew Halstead, A.R. Chase, Daniel Gilrein (2000). American Horticultural Society Pests & Diseases: The Complete Guide to Preventing, Identifying, and Treating Plant Problems (First Edition ed.). Dorling Kindersley (DK) Publishing, inc. pp. 202–203. {{cite book}}: |edition= has extra text (help)CS1 maint: multiple names: authors list (link)