Arnica, Arnica amplexicaulis (left) and other Arnica spp, widespread use of this plant is under fire because of its toxic chemistry.  Among other physiological effects, it may dramatically raise blood pressure.

Plant to left found on the slopes of Mt. Raineer.  Arnica species have opposite leaves.  Typically flowers are yellow to pale yellow, 8 to 14 ye flower rays that are toothed, squared off or rounded at the end.  (More)

Homeopathic use to fight colds.