Also known as the bulb onion or common onion, is a vegetable and is the most widely cultivated species of the genus Allium. Cepa is exclusively known from cultivation and its ancestral wild original form is not known, although escapes from cultivation have become established in some regions. The onion plant is unknown in the wild but has been grown and selectively bred in cultivation for at least 7,000 years. Archaeological and literary evidence such as the Book of Numbers 11:5 suggests that onions were probably being cultivated around two thousand years later in ancient Egypt. The ancient Egyptians worshipped it, believing its spherical shape and concentric rings symbolized eternal life. In the Middle Ages, onions were such an important food that people would pay their rent with onions, and even give them as gifts. Onions were taken by the first settlers to North America, where the Native Americans were already using wild onions in a number of ways, eating them raw or cooked in a variety of foods. They also used them to make into syrups, to form poultices and in the preparation of dyes. According to diaries kept by the colonists, bulb onions were one of the first things planted by the Pilgrim Fathers when they cleared the land for cropping. Onions were also prescribed by doctors in the early 16th century to help with infertility in women.
The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.Modern varieties typically grow to a height of 16 to 50 cm. As the onion matures, food reserves begin to accumulate in the leaf bases and the bulb of the onion grows.
Onions have particularly large cells that are readily observed under low magnification. Forming a single layer of cells, the bulb epidermis is easy to separate for educational, experimental and breeding purposes. Onions are therefore commonly employed in science education to teach the use of a microscope for observing cell structure.
Onions are high in vitamin C, a good source of fiber, and with only 45 calories per serving, add abundant flavor to a wide variety of food. Onions are sodium, fat, and cholesterol free, and provide a number of other key nutrients. Onions have an energy value of 166kJ 40 kcal per 100 g. With their unique combination of flavonoids and sulfur-containing nutrients, the allium vegetables—such as onions—belong in your diet on a regular basis. There’s research evidence for including at least one serving of an allium vegetable—such as onions—in your meal plan every day. Daily consumption of onion show robust benefits for bone density.
Onions are commonly chopped and used as an ingredient in various hearty warm dishes, and may also be used as a main ingredient in their own right. They are very versatile and can be eaten raw in salads, baked, boiled, braised, grilled, fried, roasted or sautéed,