The onion (Allium cepa), is a biennial, herbaceous plant of the Amaryllidaceae family. It is Canada's most important condiment crop. Onions are native to western Asia; their cultivation predates recorded history. Botanical varieties include A. cepa solaninum (Multiplier Onion) and A. cepa viviparum (Top or Tree Onion). The bulb is formed of hollow leaves, thickened into 1.5-5 mm fleshy layers which overlap near the root juncture. Bulb skins are usually yellow, white or red. Depending chiefly on variety, mature bulbs range from 6 cm to 14 cm in diameter. The pungent taste derives from sulphurous, volatile oils (eg, pyruvic acid). Onions germinate at temperatures of 9-30°C, tolerate frosts to -2.5°C and mature in 115-135 days. Insect pests include onion maggots and thrips; plant diseases, smut, downy mildew, pink root, damping-off, leaf spot, purple blotch and neck rot. Young, green bulbs and tops contain useful amounts of vitamins A and C; dehydrated onions contain protein, phosphorus and potassium. The annual Canadian production of dry onions is nearly 220 000 t (on more than 5500 ha), worth approximately $73.5 million; Ontario produces near one-half.