Onion

Allium cepa L.

Order: Liliales

Family: Alliaceae (was Liliaceae, Amaryllidaceae or Allioideae)

Names:

Allium is Latin for Garlic.
Cepa
Onion

Other Names:

Summary:

An aromatic, common vegetable with round, hollow leaves and an underground bulb.

Description:

Cotyledons:

Two.

Leaves:

Stipules -
Petiole -
Blade - Long, round, hollow.
Stem leaves -

Stems:

Long.

Flower head:

At the ends of the stems.

Flowers:

Ovary -
Calyx -
Perianth -
Sepals -
Petals -
Stamens -
Anthers -

Fruit:

Seeds:

Small.

Roots:

Fibrous.

Key Characters:

Biology:

Life cycle:

Biennial. Seed is planted from February to September and harvested 2-6 months later depending on variety.

Physiology:

Optimum temperature for growth 13-240C.
Frost tolerant. Cool temperatures before bulbs are formed improves yields.
Prefer dry conditions at harvest.
Flowering induced by temperatures below 100C when seedlings are greater than 6 mm diameter.
Bulb formation initiated by day lengths of 12-16 hours and bulb growth is faster at higher temperatures.

Reproduction:

By seed.

Flowering times:

Seed Biology and Germination:

Vegetative Propagules:

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread mainly by intentional planting.

Origin and History:

Central Asia.
Introduced as a vegetable crop.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Cool temperate.
Prefer temperatures from 13-240C.

Soil:

Prefers medium to heavy friable clay loams that are deep and well drained with a pH of 6-6.5, but they will grow on a wide range of soils.

Plant Associations:

Significance:

Beneficial:

A common salad and cooked vegetable.

Detrimental:

Weed of disturbed areas.

Toxicity:

Cattle and horses have been poisoned by onions dumped in fields overseas.

Symptoms:

Consumption of large quantities causes anaemia.

Treatment:

Remove stock from exposure to large quantities of onions.

Legislation:

None.

Management and Control:

Thresholds:

Eradication strategies:

Herbicide resistance:

Biological Control:

Thrips (Thrips tabaci) and Onion Maggot (Delia platura) are the main pests.
Diseases include Downy Mildew (Peronospora destructor), White Rot (Sclerotium cepivorum), Neck Rot (Botrytis spp.), Pink Rot (Pyrenochaeta terrestris) and Bulb Rot (Fusarium oxysporum).

Related plants:

Chinese Chives (Allium tuberosum)
Chives (Allium schoenoprasum)
Crow Garlic (Allium vineale) has leaves on its flowering stem and has multiple bulbs.
Field Garlic (Allium oleraceum)
Garlic (Allium sativum)
Greathead Garlic (Allium ampeloprasum)
Leek (Allium porrum)
Naples Onion (Allium neopolitanum)
Onion (Allium cepa)
Purple-flower Garlic (Allium rotundum)
Roundhead Garlic (Allium sphaerocephalon)
Sand Leek (Allium scorodoprasum ssp. scorodoprasum)
Shallot (Allium ascalonicum)
(Allium roseum) has up to 20 pink flowers and a cylindrical stem
Allium orientale
Allium paniculatum
Allium roseum
Allium scorodoprasum ssp. rotundum

Plants of similar appearance:

References:

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P64-65.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #53.4.

Reid, R.L. (1990). The Manual of Australian Agriculture. (Butterworths, Sydney). P145.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.