root graft1
noun
1A graft of a scion from one plant on to the root of another; a plant propagated by this method.
2A naturally occurring graft between the roots of neighbouring trees.
Origin
Early 19th century; earliest use found in John Loudon (1783–1843), landscape gardener and horticultural writer.
root-graft2
verb
[with object] To graft (a tree or plant), naturally or artificially, by means of a root graft.
Origin
Mid 19th century; earliest use found in Farmers' Cabinet.