Arnica /ˈɑrnɨkə/ is a genus of perennial, herbaceous plants in the sunflower family (Asteraceae). The genus name Arnica may be derived from the Greek arni, "lamb", in reference to the soft, hairy leaves.

This circumboreal and montane (subalpine) genus occurs mostly in the temperate regions of western North America, with a few species native to the Arctic regions of northern Eurasia and North America.^[2]

Arnica used to be included in the tribe Senecioneae because it has a flower or pappus of fine bristles. This was soon questioned and Nordenstam (1977) placed it tentatively in tribe Heliantheae s.l.^{[citation needed]} This arrangement also became uncertain because of the sesquiterpene lactone chemistry in certain species. Recently Arnica was placed in an unresolved clade together with Madiinae, Eupatorieae, Heliantheae s.s. and Pectidinae.

Several species, such as Arnica montana and A. chamissonis, contain helenalin, a sesquiterpene lactone that is a major ingredient in anti-inflammatory preparations (used mostly for bruises).

Arnica species are used as food plants by the larvae of some Lepidoptera species including Bucculatrix arnicella.

Arnica is also known by the names Mountain Tobacco and, somewhat confusingly, Leopard's bane and Wolfsbane—two names that it shares with the entirely unrelated genus Aconitum.