Underground stem is a term that refers to the part of a plant that lies beneath the surface of the soil. It is an important part of the plant's anatomy as it helps in storing nutrients and water, and aids in vegetative reproduction. There are several synonyms for the term underground stem, including rhizome, tuber, bulb, and corm. A rhizome is a horizontal stem that grows beneath the soil surface and sends out shoots and roots from its nodes. A tuber is a swollen root or stem that stores energy in the form of starch. A bulb is an underground stem that stores food and produces shoots and leaves, while a corm is a rounded underground stem that stores food for the plant.