What is the outside covering of a plant's root called?

The outside covering of a plant's root is called the root epidermis. It is the outermost layer of the root's dermal tissue and forms the first boundary between the root and the surrounding soil.

Root epidermal cells are usually closely packed and often lack the thick, waxy cuticle found on many above-ground plant surfaces. This relatively permeable structure helps the root absorb water and dissolved mineral ions. In many young roots, specialized epidermal cells grow outward to form root hairs, greatly increasing the surface area available for absorption.

The root epidermis is produced from the protoderm as the root develops. Near the growing tip, the root cap protects delicate dividing and elongating cells as they push through the soil. Farther back from the tip, the mature epidermal region performs most of the root's contact and absorption functions.

Botany texts may also use the terms "epiblema" or "rhizodermis," especially when emphasizing the specialized surface layer of a root. Those terms can create confusion, but "root epidermis" is the standard, broadly accepted answer for a general biology question. It should not be confused with the endodermis, which is an internal layer surrounding the vascular cylinder.