Herbalism, argueably our oldest form of medicine, uses the therapeutic properties of plants to heal.  

The ability of plants to affect human functioning is self evident (eg as poisons). There are some 270,000 known plant species, each with attributes that can affect a person physically or subtly. Although we use relatively few of these as medicines, the therapeutic scope of each is wide, being as they are more complex than pharmaceutical drugs.
Herbal medicines can be used to treat local or general conditions of any age group. They are taken most often as a tincture for oral ingestion though can also be applied to a specific area of the body.

Herbs can be powerful. Some can interact with other medications or may not be advisable in pregnancy. Part of the herbalist’s job is to oversee safety in these respects.

Herbalism is different from homeopathy although there is much overlap and knowledge of both is a real help for the practitioner.