A storage organ is a part of a plant specifically modified for storage of energy (generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Underground storage organs and the plants that bear them are sometimes called geophytes.

In common parlance, underground storage organs may be generically called roots, tubers, or bulbs, but to the botanist these are specific, technical terms, which apply only more narrowly:

• True roots:
• Tuberous root
• Storage taproot
• Modified stems:
• Corm
• Tuber
• Rhizome
• Pseudobulb
• Caudex
• Others:
• Storage hypocotyl
• Bulb

Storage organs used for food may be generically called root vegetables, although this phrase should not be taken to imply that the class only includes true roots.