Usnea is a genus of mostly pale grayish-green fruticose lichens that grow like leafless mini-shrubs or tassels anchored on bark or twigs.:203 The genus is in the family Parmeliaceae. It grows all over the world.

Members of the genus are commonly called old man's beard, or beard papa.:203 It resembles Evernia, which is also called tree moss.

Like other lichens it is a symbiosis of a fungus and an alga. In Usnea, the fungus belongs to the division Ascomycota, while the alga is a member of the division Chlorophyta.

Members of the genus are similar to those of the genus Alectoria.:148 A distinguishing test is that the branches of Usnea are somewhat elastic, but the branches of Alectoria snap cleanly off.:148lichen mostly lose family

Morphology and reproduction

As a fruticose lichen, Usnea appears as a shrub-like growth on host trees. Unlike other similar-looking fruticose lichens, species in this genus have an elastic chord or axis running through the middle of the thallus that can be revealed by gently pulling a filament apart from either end.[2] It reproduces via vegetative means through fragmentation, asexual means through soredia, or sexual means through ascogonium and spermatogonium.[3] 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.[22] Usnea looks very similar to the plant Spanish moss, so much so that the latter's Latin name is derived from it (Tillandsia usneoides, the 'Usnea-like Tillandsia').

Taxonomy

Many species have been described. A three-volume series by Józef Motyka published in 1936 and 1947 distinguished 451 species.[6] 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.[23] It is now noted as including more than 600 species and being one of the largest genera within the Parmeliaceae.[24] The species Usnea longissima was renamed Dolichousnea longissima in 2004.[11]

Ecology

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.[12]

Usnea is very sensitive to air pollution, especially sulfur dioxide.[13] 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. It can sometimes be used as a bioindicator, because it tends to only grow in those regions where the air is clean, and of high quality.

Uses

Medical claims

According to Paul Bergner, Author of Medical Herbalism. "The usnic acid in Usnea is effective against gram positive bacteria such as Streptococcus and Staphylococcus, making Usnea a valuable addition to herbal formulas for sore throats and skin infections. It is also effective against a bacterium that commonly causes pneumonia Table 19.x shows some conditions that Usnea has been used for in European research."[14]

There is reason to believe that Usnea, in high concentrations, could possess some toxicity. The National Toxicology Program is currently evaluating the issue.[15]

Dyes

Usnea species have been used to create orange, yellow, green, blue, and purple dyes for textiles.[16][17]

Cosmetics

Usnea barbata has been used in cosmetic production for its antimicrobial and antifungal properties as a preservative and deodorant.[18]

Combustible

Usnea barbata when dry is extremely flammable and is often used as a firestarter.

Species

There are about 87 species of Usnea.[19]

Notes

  1. Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, ISBN 978-0-300-19500-2
  2. 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. 
  3. Brodo, Irwin M.; Sylvia Duran Sharnoff; Stephen Sharnoff; Canadian Museum of Nature (2001). . Yale University Press. pp. 709–710. ISBN 9780300082494. Retrieved 6 December 2012. 
  4. Marand, Sajan (5 January 2010). "Usnea". . Calicut University. pp. 87–90. Retrieved 6 December 2012. 
  5. . Food Technol. Biotechnol. 47 (1): 7–12. 2009. ISSN . 
  6. Motyka, Józef. . 
  7. Halonen, Pekka (2000). (PDF). Oulu, Finland: Oulu University Library. p. 13. ISBN 9514255232. ISSN . Retrieved 6 December 2012. 
  8. Wirtz, Nora; Printzen, Christian; Sancho, Leopoldo G.; Lumbsch, Thorsten H. (1 May 2006). . Taxon. 55 (2): 367–376. ISSN . Retrieved 5 December 2012. 
  9. Articus, Kristina (November 2004). (PDF). Taxon. 53 (4): 925–934. ISSN . Retrieved 5 December 2012. 
  10. Brodo, Irwin M.; Sylvia Duran Sharnoff; Stephen Sharnoff; Canadian Museum of Nature (2001). . Yale University Press. pp. 57–58. ISBN 9780300082494. Retrieved 6 December 2012. 
  11. Batty, Lesley C.; Hallberg, Kevin B., eds. (2010). . 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. 
  12. 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. 
  13. . Testing Status of Agents at NTP. National Toxicology Program. Retrieved 5 December 2012. 
  14. Bolton, Eileen M. (1991). (2 ed.). Julia Bolton Holloway. p. 27. ISBN 9781566590013. 
  15. Casselman, Karen Diadick (2001). . Courier Dover Publications. pp. 33–36. ISBN 9780486412313. 
  16. Ash, Michael; Irene Ash (2004). "Lichen (Usnea barbata) extract". . Synapse Info Resources. p. 437. ISBN 9781890595661. Retrieved 6 December 2012. 
  17. . USDA PLANTS. United States Department of Agriculture, Natural Resources Conservation Service. Retrieved 4 December 2012. 
  18. . Retrieved 3 December 2014. 
  19. Gadea, A., Le Pogam, P., Biver, G., Boustie, J., Le Lamer, A. C., Le Dévéhat, F., & Charrier, M. (2017). "Which Specialized Metabolites Does the Native Subantarctic Gastropod Notodiscus hookeri Extract from the Consumption of the Lichens Usnea taylorii and Pseudocyphellaria crocata?". Molecules 22(3): 425. doi: