Onion

The onion, Allium cepa, is a vegetable and the most widely cultivated species in the genus Allium, placing it in the same plant family as garlic, leeks, and chives. It is usually a biennial plant grown as an annual, with a fan of hollow, bluish-green leaves and a bulb made of shortened, compressed underground stems surrounded by fleshy modified leaves that store food reserves. If left unharvested it produces rounded clusters of white flowers with black, triangular seeds. Allium cepa is known only from cultivation, so its wild ancestor is unknown, though related wild species grow in Central Asia and Iran.