The term for the part of a plant that grows underground is "roots." Roots serve several essential functions, including anchoring the plant into the soil and absorbing water and nutrients. They also store energy and carbohydrates necessary for the growth and development of the plant. Roots can vary in structure and depth depending on the plant species and environmental conditions, with some plants exhibiting deep taproots and others having widespread fibrous root systems. The health of a plant's root system is crucial for its overall vigor and ability to thrive in diverse ecosystems.