Arnica montana, also known as leopard's bane, mountain tobacco and mountain arnica, is a moderately toxic European flowering plant in the daisy family Asteraceae that has a large yellow flower head. The names "wolf's bane" and "leopard's bane" are also used for another plant, Aconitum, which is extremely poisonous.

Arnica montana has been used as a herbal medicine, but there is insufficient clinical evidence for its therapeutic use, although studies show it helps with internal healing and preventing hematoma. It is toxic when taken internally or applied to injured skin.

Description

thumb|200px|left|Arnica montana

Arnica montana is a flowering plant about tall aromatic fragrant, herbaceous perennial. Its basal green ovate leaves with rounded tips are bright coloured and level to the ground. In addition, they are somewhat downy on their upper surface, veined and aggregated in rosettes. By contrast, the upper leaves are opposed, spear-shaped and smaller which is an exception within the Asteraceae. The chromosome number is 2n=38.

The flowering season is between May and August (Central Europe). The flower heads are composed of orange-yellow disc florets in the centre which are externally bordered by 10 to 15 yellow ray florets. The achenes have a one-piece rough pappus which opens in dry conditions. Arnica montana is a hemicryptophyte, which helps the plant to survive the extreme overwintering condition of its habitat. In addition, Arnica forms rhizomes, which grow in a two-year cycle: the rosette part grows at its front while its tail is slowly dying. The Latin specific epithet montana refers to mountains or coming from mountains. It has two accepted subspecies.

  • Arnica montana subsp. atlantica<br>Native to Portugal, Spain, and France.
  • Arnica montana subsp. montana<br>The more widespread subspecies, found in all parts of its range except for Portugal.

Arnica montana has synonyms of the species or one of its subspecies. It is absent from the Celtic Isles and the Italian and Balkan peninsulas. In addition, it is considered extinct in Hungary and Lithuania. Nevertheless, it is cultivated on a large scale in Estonia. Pseudoguaianolide sesquiterpenes constitute 0.2–0.8% of the flower head of Arnica montana. They are the toxin helenalin and their fatty esters. 2,5-Dimethoxy-p-cymene and thymol methyl ether are the primary components of essential oils from both the plant's roots and rhizomes. The quality and chemical constitution of the plant substance Arnicae flos can be monitored by near-infrared spectroscopy.

The flowers are harvested when fully developed and dried without their bract nor receptacles. The roots can be harvested in autumn and dried as well after being carefully washed.

Arnica montana is sometimes grown in herb gardens. When used as a topical medication in a gel at 50% concentration, A. montana was found to have the same effectiveness (albeit with possibly worse side effects) as a 5% ibuprofen gel for treating the symptoms of hand osteoarthritis. A 2014 review found that A. montana was ineffective at concentrations of 10% or less for pain, swelling, and bruises. A 1998 review of homeopathic A. montana (all such preparations are so dilute that they contain none of the plant) found it is no more effective than a placebo. Although a 2021 study found the drug to be more effective than placebo at preventing excessive hematoma comparable to that of anti-inflammatory substances. Contact with the plant can also cause skin irritation. In the Ames test, an extract of A. montana was found to be mutagenic. Changes in agriculture in Europe during the last decades have led to a decline in the occurrence of A. montana. Extensive agriculture has been replaced by intensive management.

References

  • Article concerning testing involving Arnica at the Royal Society of Medicine (archived)