The onion is a bulbous plant whose main use is as a food and for seasoning, but it is also used for therapeutic purposes due to the properties attributed to it by science. 
It develops numerous superficial roots that are whitish in colour. The leaves are hollow and swollen at the bottom. The bulb is formed by the thickening of the basal part of the leaves that become fleshy, white, red or violet. There are many varieties of onions grown in Italy, some typical of the spring and summer season others instead typical of the autumn and winter.