Allium cepa

The true onion, *Allium cepa*, is a vegetable that has been so thoroughly domesticated since ancient times, that the ancestral wild populations are now totally extinct. *A. cepa* is thought to be native to either Central Asia or the Middle East, as its closest wild relatives are found in those regions. Two species stand out in particular, *A. asarense* of Iran*,* and *A. vavilovii* of Turkmenistan. The former may be closest to the ancestral form of *A. cepa*, as the two readily form fertile, seed-producing hybrids (as opposed to other onion hybrids which are either infertile or are only capable of producing miniature bulbs instead of seeds). *A. vavilovii* is notable because there is a great deal of discussion over whether or not Vavilov’s onion represents a distinct and possibly ancestral species, or is merely a large population of domesticated onions that had escaped into the wilds of the Asian Steppes. Numerous other *Allium* are also called “onion,” though culinarily speaking, the “true” onion refers to those members of the genus that form large, edible bulbs, including *A. cepa*, first and foremost, or similar species like the Welsh or Japanese onion, *A. fistula*, or hybrid descendants of *A. cepa*, like the tree or Egyptian onion, *A.* x *proliferum* (a hybrid between *A. cepa* and *A. fistula*).

Evidence of onions entering into cultivation dates back over seven-thousand years. The ancient Egyptians made extensive use of the onion; revering it as both a nourishing vegetable and as a symbol of immortality. The ancient Greeks prescribed onions to their athletes to lighten the balance of blood. In the Middle Ages, onions were considered to be a commodity so valued that many peasants paid their rents in onions, and gave them as cherished gifts.

The onion is a versatile vegetable that can easily alter the flavor of any recipe depending on how thoroughly cooked it is. Raw or lightly cooked, an onion is pungent and acrid in flavor, but, as it is further cooked, the sugars with the tissues are released and caramelized, thereby changing the flavor to a more sweeter taste. The vaporization and breakdown of pungent and acrid aromatic chemicals helps to accelerate the onion’s sweetening.

There three broad categories of onions based on the color of the cut flesh: yellow, white and red. Yellow onions have the most pungent flavor and are the most frequently used in cooking. When caramelized, yellow onions turn a dark brown, as seen in French Onion soup. Red (or purple) onions are often used fresh or raw, as the reddish color is visually appealing in salads and sandwiches. Red onions are occasionally grilled, as well. White onions have the mildest pungency, and are used extensively as a staple in Mexican cuisine. When caramelized, white onions turn a golden yellow to golden brown color, and become extremely sweet (when compared to other caramelized onions). In addition to being sautéed, grilled, eaten raw, or cooked in soup, onions can be preserved in vinegar as a pickle or relish. Specific varieties of onions are bred for pickling, having been selected to mature smaller than normal. These pickling varieties are often termed “pickler,” “boiler” or “pearl” onions. This last variety should not be confused with “true” pearl onions, which are actually a variety of small, onion like leek, *A. ampeloprasum*, and are sweeter than true onions.

In addition as food, humans have used true onions as a medicinal herb for thousands of years. Topically, it can be used as an excellent antiseptic because of its various sulfur-based compounds (including sulfuric acid), and as a wart remover of questionable quality. Onion can be taken internally to help expectorate phlegm in the lungs as well as to help relieve inflammation of mucus membranes due to allergies or upper respiratory tract infections. Recent studies have shown that onions can help decrease blood sugar and cholesterol levels, as well as reduce blood pressure. Mature onions can also help to promote good intestinal health, as well as to help regulate bowel movements (as onions have been used both as a laxative and an anti-inflammatory anti-diarrheal in different situations).

Onions, as with other *Allium* species, are toxic to many animals, including dogs and cats, which lack the appropriate enzymes needed to break down the various sulfur-based chemicals inherent within these plants. If a patient is allergic to garlic, do not recommend the patient eat onions, either, unless the patient or the patient’s other health care providers state otherwise.