Arnica, << AHR nuh kuh, >> is the name of dozens of kinds of plants of the Northern Hemisphere that yield a juice used to drive away the blood that collects in bruises. The common, or mountain, arnica is the source of commercial arnica. It has a twisted root that lives from year to year. Its stem is about 2 feet (61 centimeters) high and bears heads of golden-yellow flowers. Every part of the plant contains arnicin, which is used to make the medicine. Mountain arnica is native to the mountain meadows and moors of northern and central Europe.
