Comfrey, Symphytum officinale, is a large, coarse, hairy perennial of damp ground with drooping bell-flowers and a thick black-skinned root. Its names all point one way: comfrey from the Latin confervere, to heal or grow together; the genus Symphytum from the Greek for uniting; and the country names knitbone and boneset. It was one of the most esteemed of the old wound-herbs, applied to sprains and fractures in the belief that it helped broken bones and torn flesh knit, a domestic reputation recorded here strictly as history, not as medical advice.
The belief that comfrey helped mend broken bones has a real, if partial, physical basis: the plant is unusually rich in allantoin, a compound that does encourage the growth of new skin and connective tissue in a wound, which is likely why a poultice of bruised comfrey leaf or root felt effective to generations of users, even though it could not actually knit a fractured bone beneath unbroken skin. This genuine allantoin content is also why comfrey remains a common ingredient in modern proprietary ointments for bruises and sprains, applied strictly to unbroken skin and for short periods, a continuation of the old wound-herb use under stricter modern limits.