The onion is probably native to southwestern Asia but is now grown throughout the world, chiefly in the temperate zones. The plant belongs to the lily family, Liliaceae, most members of which have an underground storage system, such as a bulb or tuber. The leaf bases of the developing plant swell to form the underground bulb that is the mature, edible onion. Most commercially cultivated onions are grown from the plant's small black seed, which is sown directly in the field, but onions may also be grown from small bulbs or from transplants. Onions are among the hardiest of all garden-vegetable plants.
Onions are among the world's oldest cultivated plants.
They were probably known in India, China, and the Middle East before recorded history. The Romans introduced the onion to Britain and, in the New World, American Indians added a highly pungent wild onion to their stews. Onions are used widely in cooking. They add flavour to such dishes as stews, roasts, soups, and salads, and are also served as a cooked vegetable. The onion's characteristic pungency results from the sulfur-rich volatile oil it contains.