Roots that arise from places other than the root system such as the lower stem are adventitious roots.
These roots arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in monocots and pteridophytes, but also in many dicots, such as clover, ivy, strawberry and willow. Most aerial roots and stilt roots are adventitious. In some conifers adventitious roots can form the largest part of the root system.