This article is about a botanical term. For electric bulb, see light bulb.

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In botany, the term bulb is used to refer to a underground or surface storage organ. It consists of a modified stem which bears swollen leaf bases, often as scales. These leaf bases generally do not support leaves, but contain food reserves to enable the plant to survive adverse weather. The leaf bases may overlap and surround the center of the bulb as with lilies, or may completely surround the inner regions of the bulb, as with the onion. The modified stem forms the base of the bulb, and plant growth occurs from this base. Roots emerge from the underside of the base, and new stems and leaves from the upper side.

Cultivated plants that form true bulbs include;

• onions, garlics, and many other Alliums,
• lily, tulips and many other members of the lily family,
• Amaryllis, Hippeastrum, Narcissus, and many other members of the Amaryllis family,
• Some species of Iris.

Some epiphytic orchids form bulb-like above ground storage organs, called pseudobulbs.

Other types of storage organ are often called bulbs. See corm, rhizome, tuber.

Bulb is one of the very few words in the English language that doesn't rhyme with anything. See List of English words without rhymes.