Onions and shallots
Family Alliaceae
Allium cepa, the onion (A. cepa 1), is a biennial herb, usually grown as an annual. A very short flattened stem is produced at the base of the plant. The cylindrical leaves (A. cepa 7) are hollow. When the plant has reached a certain stage of growth, the thickening of the leaf bases at a short distance above the stem, forms a bulb. The outer leaf bases are thin and dry. When the bulb has reached full maturity, no more leaves are produced and after a dormant period an inflorescence is formed. The long and hollow inflorescence axis bears a terminal umbel, which is an aggregate of cymes (A. cepa 8). The flowers are usually greenish-white; the fruit is a globular capsule.
Onions, compared with other fresh vegetables, are relatively high in food value. The carbohydrates mainly occur in the form of fructanes, these are polysaccharides in the form of fructose. The plant has a typical odour when bruised, due to organic sulphur compounds produced by enzyme action when the tissues are cut or injured.
Several varieties are used for food, especially on the Northern Hemisphere (A. cepa 9), (A. cepa 10), (A. cepa 11). The greatest number is found in Russia.
Distribution
The onion is believed to have originated in an area including Pakistan, Iran and other mountanious regions in Central Asia. It has been cultivated since ancient times in the Middle East and India (A. cepa 12) and was popular in ancient Egypt. The Romans took the onion, together with garlic and leek, into Western Europe. Columbus took it into the New World. Onions have now spread to most parts of the world (A. cepa 13).
Use
The bulbs are eaten raw, or may be cooked or fried as a vegetable. Small bulbs are pickled in vinegar or brine. The green leaves and white leaf bases are eaten raw.
The many varieties can be divided into three groups:
1. Allium cepa var. cepa, the common onion. This group is characterized by a great variation in shape and colour of the bulbs. They are cultivated on a large scale in the West (A. cepa 14), (A. cepa 2), (A. cepa 3), (A. cepa 4).
2. Allium cepa var. aggregatum, the shallot (A. cepa 5) produces a cluster of small bulbs. The shallot is also referred to as Allium ascalonicum. This group also includes the ‘ potato’ onion or ‘ multiplier’ onion with leaves and bulbs narrower than in the common onion.
3. Allium cepa var. proliferum (= Allium cepa var. bulbiferum, = Allium cepa var. viviparum), tree onion or Egyptian onion (A. cepa 6). The inflorescence produces a cluster of small bulbs or bulbils. They are of little commercial value.