Adventitious roots are plant roots that arise from any point other than the radicle (embryonic root) or the root axis of a plant. They can develop from stems, leaves, or other non-root plant parts. Adventitious roots are especially numerous on underground stems, such as rhizomes, corms, and tubers, and are common in most monocotyledons.

Adventitious roots can serve a variety of purposes in plants. They can play a role in vegetative reproduction, as adventitious roots from stem or leaf cuttings make it possible to asexually propagate a wide variety of horticultural plants. In addition, adventitious roots can be modified for aerial support and are called prop roots or aerial roots, as in corn (maize), screw pine, and banyan trees. Many tropical rainforest trees have large woody prop roots that develop from adventitious roots on horizontal branches and eventually reach the ground to provide additional anchorage and support.

Adventitious roots can form naturally on intact stems or wound-induced on detached stems or leaves. They form from cells in the stem or leaf through a sequential process that includes the stages of dedifferentiation, formation of root initials, development of root primordia, and finally emergence of the root through the stem. Adventitious root formation on stem or leaf cuttings is the basis for vegetative propagation for many commercial greenhouse and nursery crops.

There are different types of adventitious roots, including aerial roots that grow above ground usually from the stems of plants, and brace roots that are formed to support upright stems. Adventitious roots on some vines allow them to climb and attach to upright surfaces.

In summary, adventitious roots are plant roots that arise from non-root plant parts and can serve a variety of purposes in plants, including vegetative reproduction and aerial support. They can form naturally on intact stems or wound-induced on detached stems or leaves, and their formation on stem or leaf cuttings is the basis for vegetative propagation for many commercial greenhouse and nursery crops.