Arnicaə/ is a genus of perennial, herbaceous plants in the sunflower family (Asteraceae). The genus name Arnica may be derived from the Greekarni, "lamb", in reference to the plants' soft, hairy leaves. Arnica is also known by the names mountain tobacco and, confusingly, leopard's bane and wolfsbane—two names that it shares with the entirely unrelated genus Aconitum.
Frigid arnica near a training radar site in the Alaskan Interior.
Arnica plants have a deep-rooted, erect stem that is usually unbranched. Their downy oppositeleaves are borne towards the apex of the stem. The ovoid, leathery basal leaves are arranged in a rosette.
They show large yellow or orange flowers, 6–8 cm (2–3 in) wide with 10–15 cm (4–6 in) long ray florets and numerous disc florets. The phyllaries (a bract under the flowerhead) has long spreading hairs. Each phyllary is associated with a ray floret. Species of Arnica, with an involucre (a circle of bracts arranged surrounding the flower head) arranged in two rows, have only their outer phyllaries associated with ray florets. The flowers have a slight aromatic smell. If taken in the wrong dose it can be very dangerous.
The seedlike fruit has a pappus of plumose, white or pale tan bristles. The entire plant has a strong and distinct pine-sage odor when the leaves of mature plants are rubbed or bruised.