Allium is the onion genus, 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.
Allium species occur in temperate climates of the northern hemisphere. The flowers form an umbel the top of a leafless stalk. Some species (such as Welsh onion, A. fistulosum) develop thickened leaf-bases rather than forming bulbs as such.