Onion (Allium cepa)
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Many plants in the genus Allium are known by the common name onion but, used without qualifiers, it usually refers to Allium cepa. Allium cepa is also known as the ‘garden onion’ or ‘bulb’ onion and ‘shallot’.
Allium cepa is known only in cultivation, but related wild species occur in Central Asia. The most closely-related species include Allium vavilovii Popov & Vved. and Allium asarense R.M. Fritsch & Matin from Iran. However Zohary and Hopf warn that “there are doubts whether the vavilovii collections tested represent genuine wild material or only feral derivatives of the crop.”
Onions are available in fresh, frozen, canned, pickled, and dehydrated forms. Onions can be used, usually chopped or sliced, in almost every type of food, including cooked foods and fresh salads, and as a spicy garnish; they are rarely eaten on their own but usually act as accompaniment to the main course. Depending on the variety, an onion can be sharp, spicy, tangy and pungent or mild and sweet.
Onions pickled in vinegar are eaten as a snack. These are often served as a side serving in fish and chip shops throughout the United Kingdom. Onions are a staple food in India, and are therefore fundamental to Indian cooking. They are commonly used as a base for curries, or made into a paste and eaten as a main course or as a side dish.
Tissue from onions is frequently used in science education to demonstrate microscope usage, because they have particularly large cells which are readily observed even at low magnifications.