Arnica montana (mountain arnica) is a very old medicinal plant. The flower and flower heads are widely used in phytotherapy in numerous preparations. They have a broad spectrum of effects: bacteriostatic, fungistatic, antiinflammatory, antirheumatic, cardiotonic, and antihyperlipidemic.
The industrial demand for Arnica montana of a standardized quality in its active substances is inconsistent with the still practiced wild collection of mountain arnica, its protected status in several European countries, and the difficulties in its cultivation. There are four different approaches to meet the industrial demand for Arnica and guarantee the supply of a standardized plant drug or of its active substances:
- (1) improvement of the cultivation of Arnica montana;
- (2) cultivation of other Arnica species with a similar pharmacological effect;
- (3) micropropagation for the production of a standardized quality;
- (4) in vitro production of secondary metabolites in cell cultures.
In this chapter, literature on the distribution and importance of Arnica species and on the conventional and biotechnical approaches to their improvement and production is reviewed, and prospects for the latter approaches are discussed.
Botany, Distribution, and Importance of the Plant
The genus Arnica L. consists of about 32 species predominantly confined to the boreal and montane regions of the northern hemisphere, the greatest number of species being found in the western cordillera of North America. It belongs to the family Asteraceae and is divided into five subgenera, Andropurpurea, Arctica, Austromontana, Chamissonis, and Montana (Maguire 1943). Cytologically, the genus is very diverse, consisting of both diploid and polyploid races (2n = 38, 57, 76, and 95). The basic chromosome number of the genus is x = 19. Arnica species are rhizomatous perennial herbs with simple or branched stems bearing opposite leaves, and large, single or cymose heads of yellow flowers. The flower head is composed of many small flowers called florets. The head is surrounded by involucral bracts. Inside these bracts is a row of female ray florets lacking anthers in most of the species. Within the row of ray florets one finds a varying number of small perfect tubular disk florets with five fused anthers surrounding the style and stigma. Both the ray and disk florets have an inferior ovary, which develops into an achene, a one-seeded fruit. The flower heads and other parts of the plant of two of the species have been used therapeutically: Arnica montana (subgenus Montana) and Arnica chamissonis (subgenus Chamissonis), both of them containing sesquiterpene lactones as pharmacologically active compounds. Sesquiterpene lactones are also found in several other Arnica species such as A. longifolia, A. mollis, A. viscosa (). These, however, are not yet of great importance as medicinal plants. For the botanical identification of the Arnica flowers, the morphology and distribution of trichomes, glands, and pappus bristles are important ()
Mountain arnica is distributed over middle, southern, and eastern Europe. The plant and its parts are included in various pharmacopeiae: flower heads in Flos/Flores Arnicae; rhizomes and roots in Rhizoma/ Radix Arnicae; the entire plant in Herba Arnicae or Tinctura Arnicae.
External applications are given as compresses or ointments for inflammation, swelling and bruises to facilitate healing, and the curing of rheumatic complaints of muscles and joints. Oral applications are given in standardized preparations as a heart tonic for patients with Anginapectoris, coronary sclerosis, and Asthma bronchiale (). Both long-term internal application and application of the medicaments in too high concentrations can produce negative side effects.
A. chamissonis is distributed over North America from Alaska to New Mexico, and due to its low ecological demand it is easier to cultivate than A. montana (). Maguire (1943) subdivided A. chamissonis according to morphological and geographical aspects into three subspecies: A. genuia, A. foliosa, and A. incana. According to the presently accepted nomenclature, the subspecies A. incana is considered to be a variety of the subspecies foliosa, leaving only two subspecies.
Apart from mountain arnica, only A. chamissonis ssp. foliosa has been approved for use in the preparation of the Arnica flower drug (officinal Arnicae flos DAB9), because of the similarity of pharmacological effects to A. montana (). Arnica flower heads contain sesquiterpene lactones as pharmacologically active substances in their glandular hairs. They are very reactive substances blocking sulfhydryl groups, which in turn act in very low concentrations by more or less selective inhibition of essential enzymes and stabilization of cell membranes. Flavonoids and essential oils, two other groups of pharmacologically active substances in the flowers are supposed to be involved in these effects. The active substance of roots and rhizomes is the essential oil.
Arnica montana and some provenances of Arnica chamissonis ssp. foliosa are attractive plant species for the pharmaceutical industry. They contain numerous sesquiterpene lactones, flavonoids and essential oils as pharmacologically active substances. Preselected populations of A. montana with improved agronomic characteristics are available as an alternative for wild-growing mountain arnica. For the selection and propagation of agronomically and pharmaceutically interesting genotypes of A. montana in vitro propagation techniques were developed. They are also of major importance in enabling the production of standardized quality products. Extracts from leaf cell cultures contain immunologically active polysaccharides.
Selections from the book: Medicinal and Aromatic Plants VIII (1995).