its a bulb
A onion is a modified stem
Onion is a modified stem because it is a stem which grows underground
The carrot, radish, onion and sugar beet have stems that are above ground and the roots and edible tuber/bulb is underground. The stem is green and the carrot is orange; the beet is red, the onion is white/red; the radish is red/white.
Onion roots emerge from the base of the condensed stem.
Onions are alliums and they are bulbs that grow underground.
An onion, strictly speaking, is a 'bulb' and is a stem.
The rounded stem or shoot of an onion is called a bulb.
stem
white
Onion is an underground stem called a bulb. It grows horizontally below the surface of the soil, from which roots grow downward and shoots emerge above ground.
Onion is not an underground stem; it is a bulb vegetable. Carrot, sugarcane, and turnip have underground stems that store nutrients and help the plants grow.