Allium cepa
Lily family.
Onion is the underground bulb-shaped yellow red violet of a small plant, which has its green branches and green round, which are hollow inside. The white onion is harvested in late spring and color are collected in late summer.
For storage, must be dry, smooth and dry skin under his brown, which is what protects it from light and moisture.
Do not store them in the fridge ever, but a dry, light and airy.
A trick, not to mourn when short, is to put them in the freezer or refrigerator 10 min. before cutting.