rhizome

Horizontal underground plant stem capable of producing the upward shoot and downward root systems of a new plant. This capability allows vegetative (asexual) propagation and enables plants to survive an annual unfavourable season underground. In some plants (e.g., water lilies, many ferns, and forest herbs), the rhizome is the only stem of the plant. In such cases, only the leaves and flowers are readily visible.

Find more information on rhizome. Upgrade to Britannica Online for more on rhizome.