Rhizomes are a type of underground stem that plants use to store food material. Rhizomes have nodes and scaly leaves, and they are found on plants such as ginger and turmeric. Another example of an underground stem is a tuber, such as a potato, which grows from a plant's lower leaves.
Plants typically use underground stems to protect themselves from threats such as animal attacks and poor weather. The extra nutrients stored in these stems can be used when the plant is unable to make new food. Underground stems can be distinguished from roots by the presence of scale leaves and a terminal bud at the end of the stem.
There are four main types of underground stems: rhizomes, tubers, bulbs and corms. Rhizomes are thick underground stems that grow horizontally and develop roots on their lower surfaces. Tubers are swollen nodules that have irregular shapes due to the deposits of starch within them. The surface of a tuber usually contains several axillary buds, each of which is capable of growing into a new plant. Potato eyes are axillary buds.
Bulbs are flattened, disc-shaped underground stems that have roots growing from their lower ends. Onions and garlic are examples of bulbs. Corms are portions of the plant's main stem that are found underground. When the above-ground stem dies at the end of the growing season, the corm often remains active so that a new above-ground stem can emerge in the spring. Examples of corns include Amorphophallus and Colocasia.