Arnica

Arnica (Ár-ni-ca) is a genus with about 30 perennial, herbaceous species, belonging to the sunflower family (Asteraceae). The genus name Arnica may be derived from the Greek arna, "lamb", in reference to the soft, hairy leaves.

This circumboreal and montane genus occurs mostly in the temperate regions of western North America, while two are native to Eurasia (A. angustifolia and A. montana).

Arnica used to be included in the tribe Senecioneae, because it has a pappus of fine bristles. This was soon questioned and Nordenstam (1977) placed it tentatively in tribe Heliantheae s.l.

This arrangement also became uncertain because of the sesquiterpene lactone chemistry in certain species. Lately Arnica was placed in an unresolved clade together with Madiinae, Eupatorieae, Heliantheae s.s. and Pectidinae.

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

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

They have a deep-rooted, erect stem, that is usually unbranched. Their downy, opposite leaves 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 wide with 10-15 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.

The seed-like 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.



Source: http://en.wikipedia.org/wiki/Arnica



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