As it sometimes happens, Arnica is both the common name of the plant as
well as the genus. There are twelve species of arnica found in the Rocky Mountains(!), which is somewhat unique in the plant world, though more common in the Asteraceae family than any other. In Colorado, we have six species, including: cordifolia, latifolia, mollis, fulgens, longifolia, and parryi. Most of them prefer to grow in moist sights such as meadows, thickets and woodlands, though they each grow at different elevations. The most commonly seen species in Colorado is cordifolia, which graces the floor of aspen groves and pine forests. It has solitary yellow flowers (one flower per stalk), with yellow centers and 9-16 yellow “petals”. The leaves are opposite on the stem, heart shaped, toothed and hairy. They bloom from June-August.
Arnica is a plant that has been used for centuries as a topical healing agent, mostly in the form of poultices, salves and liniments. It is one of the best external remedies for bruises, sprains, strains, swollen feet, muscle trauma and rheumatism. It relieves pain and inflammation and potentiates the healing of damaged tissue. One of the best external applications is arnica infused oil, which is essentially the fresh leaf and flower (and sometimes root) infused in a carrier oil (like olive oil) then strained. Arnica should never be used internally, as it is potentially toxic. Nor should it ever be used on broken skin, as the toxins can enter the bloodstream this way.
Arnica is also a very popular homeopathic remedy and is entirely safe to take internally. The homeopathic preparation is used for the same conditions as mentioned above, and I often recommend both external use of arnica oil and internal use of the homeopathic for strains and sprains and bruising. It is truly one of the best for these conditions!
As with any topical application, it is wise to do a test patch first, as arnica can cause an allergic response in some people.