New roots may arise from atypical locations; these are called adventitious roots. Most commonly, adventitious roots arise out of stems, beginning from stem cortex cell divisions or from buds buried in the bark. In some plants, adventitious roots form on leaves. The field of horticulture is based in large part on cloning plants from cuttings of stems or leaves that form adventitious roots. These roots are also common along rhizomes of ferns, clubmosses, and horsetails. Primary roots and adventitious roots have similar function and structure.