The genus Allium comprises more than 600 different species, which are found throughout North America, Europe, North Africa, and Asia. Approximately 30 species have been regularly used for edible purposes (although less than half of these are subject to cultivation), with the most important being onions, garlic, leeks, chives, and shallots.

In terms of their common botanical characteristics, alliums are mainly herbaceous plants, incorporating various underground storage structures made up of rhizomes, roots, and bulbs. The foliar leaves alternate, often sheathing at the base to give the superficial impression that they originate from an above-ground stem. As a rule, the flower cluster, or inflorescence, is umbrella-like, with all the flower stalks radiating from the same point (umbel); the flowers are pollinated by insects; the fruits take the form of a capsule or berry; and the seeds are numerous and endospormic.

This genus is placed in the lily family. Most, but not all, of the species possess the pungent odor typical of onion and garlic. In addition to alliums, species of Ipheion, Adenocalymma, Androstephium, Esperocallis, Talbaghia, Nectarosiordum, Nilula, and, possibly, Descurainia produce pungent odors (Fenwick and Hanley 1985a).

Onions

History

Antiquity. The onion (Allium cepa) may have originated in Persia (Iran) and Beluchistan (eastern Iran and southwestern Pakistan). But it is also possible that onions were indigenous from Palestine to India. They have been known and cultivated for many thousands of years and no longer grow wild. Their range – virtually worldwide – now includes China, Japan, Europe, northern and southern Africa, and the Americas (Hedrick 1972).