Usnea is the generic and scientific name for several species of lichen in the family Parmeliaceae, that generally grow hanging from tree branches, resembling grey or greenish hair. It is sometimes referred to commonly as Old Man's Beard, Beard Lichen, or Treemoss. Usnea looks very similar to Spanish moss, so much so that the latter plant's Latin name is derived from it (Tillandsia usneoides, the 'Usnea-like Tillandsia').
Many species have been described. A monography by Józef Motyka from 1947 distinguished 451 species. Many of these are now regarded as morphological varieties and adaptations to local circumstances. The taxonomic categorization of many members of this genus remains uncertain. The number of recognized species in Finland is decreasing for this reason, from 34 in 1951 to 25 in 1963 and only 12 in 2000. It is now noted as including more than 600 species and being one of the largest genera within the Parmeliaceae.(Ref. Wirtz, N. et al. 2006.)
Usnea is very sensitive to air pollution, especially sulfur dioxide. Under bad conditions they may grow no larger than a few millimetres, if they survive at all. Where the air is unpolluted, they can grow to 10–20 cm long.
Usnea has been used medicinally for at least 1000 years. Usnic acid (C18H16O7), a potent antibiotic and antifungal agent is found in most species. This, combined with the hairlike structure of the lichen, means that Usnea lent itself well to treating surface wounds when sterile gauze and modern antibiotics were unavailable. It is also edible and high in vitamin C.
In modern American herbal medicine, Usnea is primarily used in lung and upper respiratory tract infections, and urinary tract infections. There are no human clinical trials to either support or refute either practice, although in vitro research does strongly support Usnea's antimicrobial properties.
Usnea also has shown usefulness in the treatment of difficult to treat fish infections in aquariums and ponds; in part due to the Usnic Acid for digestive internal infections or external infections, and as well for gill infections/stress due to Mucilage which is also contained in Usnea.
Usnea was one ingredient in a product called Lipokinetix, promoted to induce weight loss via increase in metabolic rate. Lipokinetix has been the topic of an FDA warning in the USA, due to potential hepatotoxicity, although it is unclear yet if any toxicity would be attributable to the Usnea. Lipokinetix also contained PPA, caffeine, yohimbine and diiodothyronine. There is reason to believe that usnic acid, in high concentrations, could possess some toxicity. The National Toxicology Program is currently evaluating the issue.
There is no formal scientific information on the safety or efficacy of oral use of Usnea, although its long history of use strongly suggests value.
Some of the species of Usnea include:
- Usnea barbata
- Usnea dasypoga
- Usnea florida
- Usnea hirta
- Usnea rubicunda
- Usnea rubiginea
- Usnea scabrida
- Usnea subfloridana
- Usnea strigosa
- The species Usnea longissima was renamed Dolichousnea longissima in 2004.
- Edible and Medicinal plants of the West, Gregory L. Tilford, ISBN 0-87842-359-1
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