Onion

Allium cepa

The onion , which is also known as the bulb onion, common onion is the most widely cultivated species of the genus ''Allium.'' The genus ''Allium'' also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion , Egyptian onion , and Canada onion . The name "wild onion" is applied to a number of ''Allium'' species. Onion is most frequently a biennial, although it can also be a triennial or a perennial.

The vast majority of cultivars of ''A. cepa'' belong to the "common onion group" and are usually referred to simply as "onions". The Aggregatum Group of cultivars includes both shallots and potato onions.

''Allium cepa'' is known exclusively in cultivation, but related wild species occur in Central Asia. The most closely related species include ''Allium vavilovii'' and ''Allium asarense'' from Iran. However, Zohary and Hopf warn that "there are doubts whether the ''A. vavilovii'' collections tested represent genuine wild material or only feral derivatives of the crop."

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