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, Tree's Dandruff, Woman's Long Hair, or Tree Moss. It should not be confused with Oak Moss (genus Evernia), which it physically resembles and is also called Tree Moss. Usnea grows all over the world. Like other lichens it is a symbiosis of a fungus and an alga. The fungus belongs to the division Ascomycota, while the alga is a member of the division Chlorophyta.
Morphology and reproduction 
As a fruticose lichen, Usnea appears as a shrub-like growth on host trees. It reproduces via vegetative means through fragmentation, asexual means through soredia, or sexual means through ascogonium and spermatogonium. The growth rate of lichens in nature is slow, but the growth rate has been sped up in laboratory conditions where Usnea is being cultured. 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 three-volume series by Józef Motyka published in 1936 and 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. The species Usnea longissima was renamed Dolichousnea longissima in 2004.
Like other lichens, Usnea often grows on sick or dying trees due to the pre-existing loss of canopy leaves, allowing for greater photosynthesis by the lichen's algae; this leads some gardeners to mistakenly blame the lichen for the tree's leaf loss and illness.
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.
Medicinal uses 
Usnea has been used medicinally for at least 1600 years. Usnic acid (C18H16O7), a potent antibiotic and antifungal agent is found in all 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. Usnea has been used both internally and topically, but due to potential hepatoxicity issues, it is recommended in some medical literature to be used only externally. Usnea is high in vitamin C.
In modern American herbal medicine, Usnea barbata is used as an antibiotic, primarily used in lung and upper respiratory tract infections, and urinary tract infections. Usnea has been used as an antibiotic for gram-positive bacteria, and as an antifungal against Candida albicans. There are no human clinical trials to either support or refute either practice, although in vitro research does strongly support Usnea's antimicrobial properties.
In Germany, the Commission E approved Usnea for mild inflammation of the oral and pharyngeal mucosa in 1989.
Usnea also has shown anecdotal usefulness in the treatment of difficult to treat fish infections in aquariums and ponds.
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 Usnea, 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.
Usnea species have been used to create orange, yellow, green, blue and purple dyes for textiles.
Usnea barbata has been used in cosmetic production for its antimicrobial and antifungal properties as a preservative and deodorant.
The PLANTS database lists 86 different species of Usnea. Some of the species of Usnea include:
- Usnea barbata
- Usnea dasypoga
- Usnea florida
- Usnea hirta
- Usnea rubicunda
- Usnea rubiginea
- Usnea scabrida
- Usnea sphacelata
- Usnea subfloridana
- Usnea strigosa
Usnea filipendula, Schwäbisch-Fränkischer Wald, Germany
Usnea filipendula, Schwäbisch-Fränkischer Wald, Germany
Usnea species, Bohemian Forest, Czech Republic
Usnea species, Bohemian Forest, Czech Republic
- ^ Jellin, JM; Gregory P., Batz F., Hitchens, K., et. al. (2000). "USNEA". Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database (3rd ed.). Stockton, CA: Therapeutic Research Facility. pp. 1048–1049. ISBN 0967613647.
- ^ Marand, Sajan (5 January 2010). "Usnea". A Text Book of Botany: Vol. III. Calicut University. pp. 87–90. Retrieved 6 December 2012.
- ^ "Optimization of Culture Conditions for Lichen Usnea ghattensis G. Awasthi to Increase Biomass and Antioxidant Metabolite Production". Food Technol. Biotechnol. 47 (1): 7–12. 2009. ISSN 1330-9862.
- ^ Motyka, Józef. Lichenum generis usnea.
- ^ Halonen, Pekka (2000). Studies on the lichen genus Usnea in East Fennoscandia and Pasific North America. Oulu, Finland: Oulu University Library. p. 13. ISBN 9514255232. ISSN 03553191. Retrieved 6 December 2012.
- ^ Wirtz, Nora; Printzen, Christian; Sancho, Leopoldo G.; Lumbsch, Thorsten H. (1 May 2006). "The phylogeny and classification of Neuropogon and Usnea (Parmeliaceae, Ascomycota) revisited". Taxon 55 (2): 367–376. ISSN 0040-0262. Retrieved 5 December 2012.
- ^ Articus, Kristina (November 2004). "Neuropogon and the phylogeny of Usnea s.l. (Parmeliaceae, Lichenized Ascomycetes)". Taxon 53 (4): 925–934. ISSN 0040-0262. Retrieved 5 December 2012.
- ^ Brodo, Irwin M.; Sylvia Duran Sharnoff, Stephen Sharnoff, Canadian Museum of Nature (2001). Lichens of North America. Yale University Press. pp. 57–58. ISBN 9780300082494. Retrieved 6 December 2012.
- ^ Batty, Lesley C., & Hallberg, Kevin B., ed. (2010). Ecology of Industrial Pollution. Ecological Reviews. Cambridge University Press. p. 49. ISBN 9780521514460. Retrieved 4 December 2012. "Usnea spp., at one time widespread and luxuriant, almost entirely disappeared from a major area of England and Wales covering at least 68 000 km² and at least 6 000 km² of lowland Scotland, mainly as a result of the increase in atmospheric pollution."
- ^ Buhner, Stephen Harrod (1999). Herbal Antibiotics : Natural Alternatives for Treating Drug-resistant Bacteria (eBook ). Storey Books. p. 58. ISBN 9781580171489. "Compounds in the lichens that inhibit bacteria are usnic acid, protolichesterinic acid, some orcionol derivatives, and several (as usual) unidentified substances. Of those, the strongest is usnic acid, present in all usnea species."
- ^ Tilford, Gregory L. (1997). "Usnea Lichen". Edible and Medicinal Plants of the West. Mountain Press Publishing. pp. 146–147. ISBN 9780878423590. Retrieved 6 December 2012.
- ^ Buhner, Stephen Harrod (1999). Herbal Antibiotics : Natural Alternatives for Treating Drug-resistant Bacteria (eBook ). Storey Books. p. 58. ISBN 9781580171489. "May be used externally as a tincture, wash or powder. May be used internally as a tea, tincture, spray or douche."
- ^ Dharmananda, Subhuti. "Usnea: an herb used in Western and Chinese medicine". Safety Issues Affecting Herbs. Institute for Traditional Medicine. Retrieved 6 December 2012.
- ^ "USNEA". WebMD - Vitamins & Supplements. WebMD. Retrieved 6 December 2012. "Usnea is POSSIBLY SAFE when used on the skin, though allergic reactions can occur. The safety of taking usnea by mouth is unknown, though there are concerns that the sodium usniate (usnic acid) that it contains might cause liver damage."
- ^ Page, Linda (2008). Healthy Healing's Detoxification: Programs to Cleanse, Purify & Renew. Healthy Healing, Inc. p. 213. ISBN 9781884334559. Retrieved 6 December 2012.
- ^ Eskinazi, Daniel (1999). "Unconventional Medicine in the United States". Botanical Medicine : Efficacy, Quality Assurance, and Regulation. M.A. Liebert. p. 188. ISBN 9780585277981.
- ^ Cabrera, C. (1996). "Materia Medica - Usnea spp.". European Journal of Herbal Medicine 2 (2): 11–13. ISSN 1352-4755.
- ^ B.C. Behera, Neeraj Verma, Anjali Sonone, Urmila Makhija (January, 2006). "Determination of antioxidative potential of lichen Usnea ghattensis in vitro".
- ^ Mark Blumenthal, ed. (1998). "Usnea". The Complete German Commission E Monographs. Austin, Texas: American Botanical Council. p. 224. ISBN 0-96555550x .
- ^ "USNEA; USING USNIC ACID AS A FISH REMEDY FOR TUMORS AND MORE.". Aquarium Pond Answers. Retrieved 5 December 2012.
- ^ "Safety Alerts for Human Medical Products > Lipokinetix". MedWatch: The FDA Safety Information and Adverse Event Reporting Program. U.S. Food and Drug Administration. November 20, 2001. Retrieved 5 December 2012. "FDA has received multiple reports of persons who developed liver injury or liver failure while using Lipokinetix. The product contains norephedrine (also known as phenylpropanolamine or PPA), caffeine, yohimbine, diiodothyronine, and sodium usniate."
- ^ Jellin, JM; Gregory P., Batz F., Hitchens, K., et. al. (2000). "USNEA". Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database (3rd ed.). Stockton, CA: Therapeutic Research Facility. pp. 1048–1049. ISBN 0967613647. "Adverse reactions are uncommon in appropriate amounts. Poisoning can be possible, although signs of poisoning have not yet been described."
- ^ "Testing Status: Usnea lichen 09063". Testing Status of Agents at NTP. National Toxicology Program. Retrieved 5 December 2012.
- ^ Bolton, Eileen M. (1991). Lichens for Vegetable Dying (2 ed.). Julia Bolton Holloway. p. 27. ISBN 9781566590013.
- ^ Casselman, Karen Diadick (2001). Lichen Dyes: The New Source Book. Courier Dover Publications. pp. 33–36. ISBN 9780486412313.
- ^ Ash, Michael; Irene Ash (2004). "Lichen (Usnea barbata) extract". Handbook of Preservatives. Synapse Info Resources. p. 437. ISBN 9781890595661. Retrieved 6 December 2012.
- ^ "PLANTS profile for Usnea (beard lichen)". USDA PLANTS. United States Department of Agriculture, Natural Resources Conservation Service. Retrieved 4 December 2012.