The root of the onion is eaten and used in cooking. Many vegetables, such as carrots, turnips, radishes and beets, are all roots.
Some vegetables like lettuce and spinach have large, complicated leaf structures. These leaves are used in cooking and cuisine, while the roots are often discarded or composted. Brussels sprouts, kale and chard are more examples of plants where only the leaves are regularly consumed. Seeds, such as kidney beans and peas, are also commonly eaten. The same is true of the fruit of many vegetables, such as tomatoes, squash, eggplants and okra.
Onions have been grown as a staple food for at least 5,000 years, and they grow wild all over the world. Their watery composition makes them a valuable way to stave off thirst while traveling, while their durability allows them to be kept in storage for long periods of time. Dried onions last even longer.
Onions grow readily in different soils, and while their place of origin is unknown because they decompose fully and do not leave traces, it is known that they were farmed in Ancient China, Egypt and other early civilizations. In Egypt, they represented eternal life and were often buried with the dead for use in the afterlife.