Editing Lichen (section)

== Human use ==
{{Further|Ethnolichenology}}

[[File:Hiroshige II - Kishu kumano iwatake tori - Shokoku meisho hyakkei.jpg|thumb|upright|[[Iwatake]] (''Umbilicaria esculenta'') gathering at Kumano in Kishū, by [[Hiroshige II]]]]

=== Food ===
{{Main|Edible lichen}}
Lichens are eaten by many different cultures across the world. Although some lichens are only eaten in times of [[famine]], others are a [[staple food]] or even a [[delicacy]]. Two obstacles are often encountered when eating lichens: lichen [[polysaccharide]]s are generally indigestible to humans, and lichens usually contain mildly toxic [[secondary compound]]s that should be removed before eating. Very few lichens are poisonous, but those high in [[vulpinic acid]] or [[usnic acid]] are toxic.<ref name="Emmerich1993"/> Most poisonous lichens are yellow.{{citation needed|date=February 2024}}

In the past, [[Iceland moss]] (''Cetraria islandica'') was an important source of food for humans in northern Europe, and was cooked as a bread, porridge, pudding, soup, or salad. It is also fed to cattle, pigs and ponies. ''[[Bryoria fremontii]]'' (edible horsehair lichen) was an important food in parts of North America, where it was usually [[Pit barbecue|pitcooked]]. Northern peoples in North America and Siberia traditionally eat the partially digested [[Cladonia rangiferina|reindeer lichen]] (''Cladina'' spp.) after they remove it from the [[rumen]] of caribou or reindeer that have been killed. [[Rock tripe]] (''Umbilicaria'' spp. and ''Lasalia'' spp.) is a lichen that has frequently been used as an emergency food in North America, and one species, ''[[Umbilicaria esculenta]]'', (''iwatake'' in Japanese) is used in a variety of traditional Korean and Japanese foods.<ref>{{Cite journal |last=Llano |first=George A. |date=1948 |title=Economic uses of lichens |url=http://link.springer.com/10.1007/BF02907917 |journal=Economic Botany |language=en |volume=2 |issue=1 |pages=15–45 |doi=10.1007/BF02907917 |issn=0013-0001}}</ref>

=== Lichenometry ===
{{Main|Lichenometry}}
[[File:Lichen forming a Hidden Mickey.jpg|thumb|left|Lichen grown in a [[Mickey Mouse]] shape]]
[[File:Lichen Mickey 13 years later.jpg|thumb|left|13 years later]]
Lichenometry is a technique used to determine the age of exposed rock surfaces based on the size of lichen thalli. Introduced by Beschel in the 1950s,<ref name=Beschel1950/> the technique has found many applications. it is used in [[archaeology]], [[palaeontology]], and [[geomorphology]]. It uses the presumed regular but slow rate of lichen growth to determine the [[Surface exposure dating|age of exposed rock]].<ref name=LSN/>{{rp|9}}<ref>Curry, R. R. (1969) "Holocene climatic and glacial history of the central Sierra Nevada, California", pp. 1–47, Geological Society of America Special Paper, 123, S. A. Schumm and W. C. Bradley, eds.</ref> Measuring the diameter (or other size measurement) of the largest lichen of a species on a rock surface indicates the length of time since the rock surface was first exposed. Lichen can be preserved on old rock faces for up to{{citation needed|date=August 2014}} 10,000 years, providing the maximum age limit of the technique, though it is most accurate (within 10% error) when applied to surfaces that have been exposed for less than 1,000 years.<ref>Sowers, J. M., Noller, J. S., and Lettis, W. R. (eds.) (1997) ''Dating and Earthquakes: Review of Quaternary Geochronology and its Application to Paleoseismology''. US Nuclear Regulatory Commission, NUREG/CR 5562.</ref> Lichenometry is especially useful for dating surfaces less than 500 years old, as [[radiocarbon dating]] techniques are less accurate over this period.<ref name="innes">{{cite journal |doi=10.1177/030913338500900202 |title=Lichenometry |journal=Progress in Physical Geography |volume=9 |issue=2 |page=187 |year=1985 |last1=Innes |first1=J. L.|bibcode=1985PrPG....9..187I |s2cid=220949784 }}</ref> The lichens most commonly used for lichenometry are those of the genera ''[[Rhizocarpon]]'' (e.g. the species ''[[Rhizocarpon geographicum]]'', map lichen) and ''[[Xanthoria]]''.

===Biodegradation===
Lichens have been shown to degrade [[polyester resin]]s, as can be seen in archaeological sites in the Roman city of [[Baelo Claudia]] in Spain.<ref>{{cite journal|pmc=2227722|title=Microorganisms Attack Synthetic Polymers in Items Representing Our Cultural Heritage|author1=Cappitelli, Francesca |author2=Sorlini, Claudia |journal=Applied and Environmental Microbiology|date=2008|volume=74|issue=3|pmid=18065627|doi=10.1128/AEM.01768-07|pages=564–569|bibcode=2008ApEnM..74..564C}}</ref> Lichens can accumulate several environmental pollutants such as lead, copper, and [[radionuclide]]s.<ref name="gadd">{{Cite journal|author-link=Geoffrey Michael Gadd|author=Gadd, Geoffrey Michael|date=March 2010|title=Metals, minerals and microbes: geomicrobiology and bioremediation|journal=Microbiology|volume=156|issue=Pt 3|pages=609–643|doi=10.1099/mic.0.037143-0|pmid=20019082|doi-access=free}}</ref> Some species of lichen, such as ''[[Parmelia sulcata]]'' (called a hammered shield lichen, among other names) and ''[[Lobaria pulmonaria]]'' (lung lichen), and many in the [[Cladonia|''Cladonia'' genus]], have been shown to produce [[serine protease]]s capable of the degradation of pathogenic forms of [[prion protein]] (PrP), which may be useful in treating contaminated environmental reservoirs.<ref>{{Cite journal|last1=Johnson|first1=Cristopher J|last2=Bennet|first2=James P|last3=Biro|first3=Steven M|last4=Duque-Velasquez|first4=Juan Camilo|last5=Rodriguez|first5=Cynthia M.|last6=Bessen|first6=Richard A|last7=Rocke|first7=Tonie E|date=May 2011|editor-last=Bartz|editor-first=Jason C|title=Degradation of the Disease-Associated Prion Protein by a Serine Protease from Lichens|journal=PLOS ONE|volume=6|issue=5|pages=e19836|doi=10.1371/journal.pone.0019836|pmid=21589935|pmc=3092769|bibcode=2011PLoSO...619836J|doi-access=free}}</ref><ref>{{Cite journal|last1=Rodriguez|first1=Cynthia M|last2=Bennet|first2=James P|last3=Johnson|first3=Cristopher J|date=1 January 2012|title=Lichens: Unexpected anti-prion agents?|url=https://www.ncbi.nlm.nih.gov/p|journal=Prion|volume=6|issue=1|pages=11–16|doi=10.4161/pri.6.1.17414|pmid=22453171|pmc=3338958}}</ref><ref>{{Cite journal|last1=Bennet|first1=James P|last2=Rodriuguez|first2=Cynthia M|last3=Johnson|first3=Cristopher|date=July 2012|title=Prion protein degradation by lichens of the genus Cladonia|url=https://www.researchgate.net/publication/259423529|journal=The Lichenologist|volume=44|issue=4|pages=523–531|doi=10.1017/S0024282912000102|s2cid=85819801}}</ref>

=== Dyes ===
Many lichens produce secondary compounds, including [[Biological pigment|pigments]] that reduce harmful amounts of sunlight and powerful toxins that deter [[herbivore]]s or kill bacteria. These compounds are very useful for lichen identification, and have had economic importance as [[dye]]s such as [[cudbear]] or primitive [[antibiotics]].

A [[pH indicator]] (which can indicate acidic or basic substances) called [[litmus]] is a dye extracted from the lichen ''[[Roccella tinctoria]]'' ("dyer's weed")<ref>{{Cite web|title=A Modern Herbal {{!}} Litmus|url=https://www.botanical.com/botanical/mgmh/l/litmus35.html#med|access-date=2021-10-24|website=botanical.com}}</ref> by boiling.  It gives its name to the well-known [[Litmus test (chemistry)|litmus test]].

[[Traditional dyes of the Scottish Highlands]] for [[Harris tweed]] and other traditional cloths were made from lichens, including the orange ''[[Xanthoria parietina]]'' ("common orange lichen") and the grey foliaceous ''[[Parmelia saxatilis]]'' common on rocks and known colloquially as "crottle".

There are reports dating almost 2,000 years old of lichens being used to make purple and red dyes.<ref name=Casselman1999/> Of great historical and commercial significance are lichens belonging to the family ''[[Roccellaceae]]'', commonly called orchella weed or orchil. [[Orcein]] and other lichen dyes have largely been replaced by [[Dye#Natural and synthetic|synthetic versions]].

===Traditional medicine and research===
Historically, in [[traditional medicine]] of Europe, ''[[Lobaria pulmonaria]]'' was collected in large quantities as "lungwort", due to its lung-like appearance (the "[[doctrine of signatures]]" suggesting that herbs can treat body parts that they physically resemble).Similarly, ''[[Peltigera leucophlebia]]'' ("ruffled freckled pelt") was used as a supposed cure for [[candidiasis|thrush]], due to the resemblance of its cephalodia to the appearance of the disease.<ref name=Dobson/>

Lichens produce [[metabolite]]s being researched for their potential therapeutic or diagnostic value.<ref>{{cite journal | last1 = Muller | first1 = K | year = 2001 | title = Pharmaceutically Relevant Metabolites from Lichens | doi = 10.1007/s002530100684 | pmid = 11499952 | journal = Applied Microbiology and Biotechnology | volume = 56 | issue = 1–2| pages = 9–10 | s2cid = 11958438 }}</ref> Some metabolites produced by lichens are structurally and functionally similar to [[broad-spectrum antibiotics]] while few are associated respectively to antiseptic similarities.<ref name=morton>Morton, E.; Winters, J. and Smith, L. (2010). [https://deepblue.lib.umich.edu/bitstream/handle/2027.42/78342/Morton_Winters_Smith_2010.pdf?sequence=1 "An Analysis of Antiseptic and Antibiotic Properties of Variously Treated Mosses and Lichens"] {{Webarchive|url=https://web.archive.org/web/20170820033126/https://deepblue.lib.umich.edu/bitstream/handle/2027.42/78342/Morton_Winters_Smith_2010.pdf?sequence=1 |date=20 August 2017 }}. University of Michigan Biological Station</ref> [[Usnic acid]] is the most commonly studied metabolite produced by lichens.<ref name=morton/> It is also under research as a [[Bactericide|bactericidal]] agent against ''[[Escherichia coli]]'' and ''[[Staphylococcus aureus]]''.<ref>{{cite journal | last1 = Bustinza | first1 = F. | date = 1952 | title = Antibacterial Substances from Lichens | journal = Economic Botany | volume = 6 | issue = 4| pages = 402–406 | doi=10.1007/bf02984888| bibcode = 1952EcBot...6..402B | s2cid = 39335883 }}</ref>

===Aesthetic appeal===
[[File:CladonioPinetum.jpg|thumb|right|Pine forest with ''[[Cladonia]]'' lichen ground-cover]]
Colonies of lichens may be spectacular in appearance, dominating the surface of the visual landscape as part of the aesthetic appeal to visitors of [[Yosemite National Park]], [[Sequoia National Park]], and the [[Bay of Fires]].<ref name=LSN/>{{rp|2}} [[Caloplaca|Orange]] and [[Xanthoria|yellow]] lichens add to the ambience of desert trees, tundras, and rocky seashores. Intricate webs of lichens [[Usnea|hanging from tree branches]] add a mysterious aspect to forests. Fruticose lichens are used in [[model railroading]]<ref>{{cite web|url=http://yourdiorama.com/landscaping/using-lichen-on-your-model-railway-layout/|title=Themodelrailroader.com|access-date=10 October 2014|archive-url=https://web.archive.org/web/20141015193251/http://www.themodelrailroader.com/landscaping/using-lichen-on-your-model-railway-layout/|archive-date=15 October 2014|url-status=dead}}</ref> and other modeling hobbies as a material for making miniature trees and shrubs.

===In literature===
In early [[Midrashic]] literature, the Hebrew word "''vayilafeth''" in [[Book of Ruth|Ruth]] 3:8 is explained as referring to [[Ruth (biblical figure)|Ruth]] entwining herself around [[Boaz]] like lichen.<ref>Thus explained by Rabbi [[Enoch Zundel ben Joseph]], in his commentary ''Etz Yosef'' ("Tree of Joseph"), on ''Sefer [[Midrash Rabbah]]'', vol. 2, New York 1987, s.v. ''Ruth Rabba'' 6:3</ref> The 10th century Arab physician [[Al-Tamimi, the physician|Al-Tamimi]] mentions lichens dissolved in [[vinegar]] and [[rose water]] being used in his day for the treatment of skin diseases and rashes.<ref>Zohar Amar and Yaron Serri, ''The Land of Israel and Syria as Described by Al-Tamimi'', Ramat-Gan 2004, pp. 56, 108–109 {{ISBN|965-226-252-8}} (Hebrew)</ref>

The plot of [[John Wyndham]]'s science fiction novel ''[[Trouble with Lichen]]'' revolves around an anti-aging chemical extracted from a lichen.