Contemporary herbalists have an ambivalent and controversial view of comfrey, despite a tradition of use by herbalists over history. Its traditional names of knitbone, boneset and the derivation of its Latin name Symphytum (from the Greek symphis, meaning growing together of bones, and phyton, a plant), speak to its long and widespread usage as a therapeutic herb.
Comfrey (Symphytum officinale) is sometimes used on the skin to treat wounds and reduce inflammation from sprains and broken bones. Comfrey roots and leaves contain allantoin, a substance that helps new skin cells grow, along with other substances that reduce inflammation and keep skin healthy. Comfrey ointments have been used to heal bruises as well as pulled muscles and ligaments, fractures, sprains, strains, and osteoarthritis.
Definition and image from Wikipedia