Editing Lichenology (section)

==History==

===The beginnings===

Lichens as a group have received less attention in classical treatises on botany than other groups although the relationship between humans and some species has been documented from early times. Several species have appeared in the works of [[Dioscorides]], [[Pliny the Elder]] and [[Theophrastus]] although the studies are not very deep. During the first centuries of the modern age they were usually put forward as examples of [[spontaneous generation]] and their reproductive mechanisms were totally ignored.<ref>Lauder Lindsay, William (1856). ''A Popular History of British Lichens'' p. 22</ref> For centuries naturalists had included lichens in diverse groups until in the early 18th century a French researcher [[Joseph Pitton de Tournefort]] in his ''Institutiones Rei Herbariae'' grouped them into their own genus. He adopted the Latin term lichen, which had already been used by Pliny who had imported it from Theophrastus but up until then this term had not been widely employed.<ref>Lauder Lindsay, William (1856). ''A Popular History of British Lichens'' p. 23</ref> The original meaning of the Greek word λειχήν (leichen) was moss that in its turn derives from the Greek verb λείχω (liekho) to suck because of the great ability of these organisms to absorb water. In its original use the term signified [[mosses]], [[liverworts]] as well as [[lichens]]. Some forty years later [[Dillenius]] in his ''Historia Muscorum'' made the first division of the group created by Tournefort separating the sub-families [[Usnea]], Coralloides{{efn|"mostly [[Clavarieae]]", according to [[George Claridge Druce|Druce]].<ref>{{cite web |url=http://www.mobot.org/mobot/latindict/keyDetail.aspx?keyWord=coralloides |title=A Grammatical Dictionary of Botanical Latin: coralloides |first=P. M. |last=Eckel |website=[[Missouri Botanical Garden]] |date=2010–2021 |access-date=19 August 2021}}</ref>}} and [[Lichens]] in response to the morphological characteristics of the lichen [[thallus]].<ref>{{cite book |author=Joseph Pitton de Tournefort |title=Institutiones rei herbariae |language=la |trans-title=Institutions of botany |volume=1 |url=https://books.google.com/books?id=2BkOAAAAQAAJ&q=%22Tournefort%22+%22Institutiones+rei+Herbariae%22|year=1700 }}</ref>

After the revolution in [[taxonomy (biology)|taxonomy]] brought in by [[Carl Linnaeus|Linnaeus]] and his new system of classification lichens are retained in the [[Plant]] Kingdom forming a single group [[Lichen]] with eight divisions within the group according to the morphology of the [[thallus]].<ref>Lauder Lindsay, William (1856). ''A Popular History of British Lichens''. p. 24.</ref> The [[Taxonomy (biology)|taxonomy]] of lichens was first intensively investigated by the [[Sweden|Swedish]] botanist [[Erik Acharius]] (1757–1819), who is therefore sometimes named the "father of lichenology". Acharius was a student of [[Carl Linnaeus]]. Some of his more important works on the subject, which marked the beginning of lichenology as a discipline, are:

* ''Lichenographiae Suecia prodromus'' (1798)
* ''Methodus lichenum'' (1803)
* ''Lichenographia universalis'' (1810)
* ''Synopsis methodica lichenum'' (1814)
[[File:Flechte auf Fels.jpg|thumb|Lichen on rocks]]
[[File:Lichen foliacé2..JPG|thumb|[[Oakmoss]] (''Evernia prunastri'')]]

Later lichenologists include the American scientists [[Vernon Ahmadjian]] and [[Edward Tuckerman]] and the [[Russia]]n [[evolutionary biologist]] [[Konstantin Merezhkovsky]], as well as amateurs such as [[Louisa Collings]].

Over the years research shed new light into the nature of these organisms still classified as plants. A controversial issue surrounding lichens since the early 19th century is their reproduction. In these years a group of researchers faithful to the tenets of Linnaeus considered that lichens reproduced sexually and had sexual reproductive organs, as in other plants, independent of whether asexual reproduction also occurred. Other researchers only considered asexual reproduction by means of [[Propagules]].<ref>Lauder Lindsay, William. ''A Popular History of British Lichens''. p. 25.</ref>

===19th century===

Against this background appeared the Swedish botanist [[Erik Acharius]] disciple of Linnaeus, who is today considered the father of lichenology, starting the taxonomy of lichens with his pioneering study of Swedish lichens in Lichenographiae Suecicae Prodromus of 1798 or in his Synopsis Methodica Lichenum, Sistens omnes hujus Ordinis Naturalis of 1814.<ref>{{cite book |last=Acharius |first=Erik |date=1814 |title=Synopsis Methodica Lichenum: Systens omnes hujus ordinis naturalis detectas |language=la |trans-title=Synopsis of lichen Methods, systems of this natural order detected |publisher=Svanborg}}</ref> These studies and classifications are the cornerstone of subsequent investigations. In these early years of structuring the new discipline various works of outstanding scientific importance appeared such as Lichenographia Europaea Reformata published in 1831 by [[Elias Fries]] or Enumeratio Critico Lichenum Europaeorum 1850 by [[Ludwig Schaerer]]<ref>{{Cite web|url=https://plants.jstor.org/stable/history/10.5555/al.ap.person.bm000391348|title=Edit History: Schaerer, Ludwig Emanuel (Louis-Emmanuel) (1785-1853) on JSTOR|website=plants.jstor.org}}</ref> in Germany.<ref>Lauder Lindsay, William (1856). ''A Popular History of British Lichens''. p. 27.</ref>

[[File:Erik Acharius.jpg|thumb|Erik Acharius (1757–1819), Swedish botanist, the father of lichenology]] 

But these works suffer from being superficial and mere lists of species without further physiological studies.<ref>{{cite journal | last1 = Schneider | first1 = Albert | year = 1895 | title = The Biological Status of Lichens | journal = Bulletin of the Torrey Botanical Club | volume = 22 | issue = 5| pages = 189–198 | doi = 10.2307/2478161 | jstor = 2478161 }}</ref> It took until the middle of the 19th century for research to catch up using biochemical and physiological methods. In Germany {{ill|Hermann Itzigsohn|de}}<ref>{{cite web | url=http://kiki.huh.harvard.edu/databases/botanist_search.php?id=3942 | title=Harvard University Herbaria & Libraries}}</ref> and [[Johann Daniel Wilhelm Bayrhoffer|Johann Bayrhoffer]],<ref>{{cite web | url=http://kiki.huh.harvard.edu/databases/botanist_search.php?mode=details&botanistid=1617 | title=Harvard University Herbaria & Libraries}}</ref> in France [[Edmond Tulasne]] and [[Camille Montagne]], in Russia [[Fedor Buhse]],<ref>{{cite web | url=http://kiki.huh.harvard.edu/databases/botanist_search.php?id=63245 | title=Harvard University Herbaria & Libraries}}</ref> in England [[William Allport Leighton]] and in the United States [[Edward Tuckerman]] began to publish works of great scientific importance.

Scientific publications settled many unknown facts about lichens. In the French publication [[Annales des Sciences Naturelles]] in an article of 1852 "Memorie pour servir a l'Histoire des Lichens Organographique et Physiologique" by [[Edmond Tulasne]], the reproductive organs or apothecia of lichens was identified.<ref>{{cite journal | last1 = Williams | first1 = Thomas A. | year = 1856 | title = The Status of the Algo-Lichen Hypothesis | journal = The American Naturalist | volume = 23 | issue = 265 | pages = 1–8 | doi =10.1086/274846 | doi-access =  | s2cid = 84605645 }}</ref><ref>Lauder Lindsay, William (1856). ''A Popular History of British Lichens''. p. 23.</ref>

These new discoveries were becoming increasingly contradictory for scientists. The [[apothecium]] reproductive organ being unique to [[fungi]] but absent in other [[photosynthetic]] organisms. With improvements in [[microscopy]], [[algae]] were identified in the lichen structure, which heightened the contradictions. At first the presence of algae was taken as being due to contamination due to collection of samples in damp conditions and they were not considered as being in a [[symbiotic]] relation with the fungal part of the thallus. That the algae continued to multiply showed that they were not mere contaminants.

It was [[Anton de Bary]] a German [[mycologist]] who specialised in [[phytopathology]] who first suggested in 1865 that lichens were merely the result of parasitism of various fungi of the [[ascomycetes]] group by [[nostoc]] type algae and others. Successive studies such as those carried out by [[Andrei Famintsyn]] and [[Baranetzky]]<ref>{{cite web | url=http://kiki.huh.harvard.edu/databases/botanist_search.php?mode=details&id=70084 | title=Harvard University Herbaria & Libraries}}</ref> in 1867 showed no dependence of the algal component upon the lichen thallus and that the algal component could live independently of the thallus.<ref>{{cite journal | last1 = Fink | first1 = Bruce | year = 1913 | title = The Nature and Classification of Lichens: II. The Lichen and its Algal Host | doi = 10.2307/3753090 | journal = Mycologia | volume = 5 | issue = 3 | pages = 97–166 | jstor = 3753090 }}</ref> It was in 1869 that [[Simon Schwendener]] demonstrated that all lichens were the result of fungal attack on the cells of algal cells and that all these algae also exist free in nature. This researcher was the first to recognise the dual nature of lichens as a result of the capture of the algal component by the fungal component.<ref>{{cite journal | last1 = Honegger | first1 = Rosmarie | year = 2000 | title = Simon Schwendener (1829–1919) and The Dual Hypothesis of Lichens | doi = 10.1639/0007-2745(2000)103[0307:ssatdh]2.0.co;2 | journal = The Bryologist | volume = 103 | issue = 2 | pages = 307–313 | s2cid = 84580224 }}</ref> In 1873 [[Jean-Baptiste Edouard Bornet]] concluded form studying many different lichen species that the relationship between fungi and algae was purely [[symbiotic]]. It was also established that algae could associate with many different fungi to form different lichen [[phenotypes]]. 

[[File:Édouard Bornet.jpg|thumb|French botanist (Jean-Baptiste) Édouard Bornet (1828–1911)]]

===20th century===

In 1909 the Russian lichenologist [[Konstantin Mereschkowski]] presented a research paper "The Theory of two Plasms as the basis of [[Symbiogenesis]], A new study on the Origin of Organisms", which aims to explain a new theory of Symbiogenesis by lichens and other organisms as evidenced by his earlier work "Nature and Origin of [[Chromatophores]] in the Plant Kingdom". These new ideas can be studied today under the title of the Theory of [[Endosymbiosis]].<ref>{{cite journal | last1 = Cavalier-Smith | first1 = T | year = 2003 | title = Microbial Muddles | doi = 10.1641/0006-3568(2003)053[1008:mm]2.0.co;2 | journal = BioScience | volume = 53 | issue = 10 | pages = 1008 | doi-access = free }}</ref>

Despite the above studies the dual nature of lichens remained no more than a theory until in 1939 the Swiss researcher Eugen A Thomas<ref>[[Species:Eugen A. Thomas]]</ref> was able to reproduce in the laboratory the phenotype of the lichen ''[[Cladonia pyxidata]]''<ref>{{cite web | url=http://www.voyageurcountry.com/htmls/floweringplants/plants/pixiecups.html | title=Pixie Cups (Cladonia pyxidata)}}</ref> by combining its two identified components.

During the 20th century botany and mycology were still attempting to solve the two main problems surrounding lichens. On the one hand the definition of lichens and the relationship between the two symbionts and the taxonomic position of these organisms within the plant and fungal kingdoms. There appeared numerous renowned researchers within the field of lichenology such as [[Henry Nicollon des Abbayes]], [[William Alfred Weber]], [[Antonina Georgievna Borissova]], [[Irwin M. Brodo]], and [[George Albert Llano]].

Lichenology has found applications beyond [[biology]] itself in the field of [[geology]] in a technique known as [[lichenometry]] where the age of an exposed surface can be found by studying the age of lichens growing on them. Age dating in this way can be absolute or relative because the growth of these organisms can be arrested under various conditions. The technique provides an average age of the older individual lichens providing a minimum age of the medium being studied.<ref>{{cite book |title=Procesos biofísicos actuales en medios fríos: estudios recientes |language=es |trans-title=Current biophysical processes in cold environments: recent studies |editor=Antonio Gómez Ortiz |date=1998 |publisher=Edicions Universitat Barcelona |url=https://books.google.com/books?id=r_LQ70GnOnoC&q=lichenometry&pg=RA1-PA327|isbn=9788447519231 }} Miguel Mateo Garcia, The Growth Curve of Rhizocarpon geographicum in the Valley of Madriu Andorra, Biophysical Processes in Cold Media {{ISBN|84-475-1923-6}}</ref> Lichenometry relies upon the fact that the maximum diameter of the largest thallus of an [[epilithic]] lichen growing on a substrate is directly proportional to the time from first exposure of the area to the environment as seen in studies by [[Roland Beschel]]<ref>{{cite web|url=http://www.geomorphology.org.uk/assets/publications/subsections/pdfs/OnsitePublicationSubsection/91/4.2.7_lichenometry.pdf |title=Archived copy |access-date=2014-01-21 |url-status=dead |archive-url=https://web.archive.org/web/20140203072554/http://www.geomorphology.org.uk/assets/publications/subsections/pdfs/OnsitePublicationSubsection/91/4.2.7_lichenometry.pdf |archive-date=2014-02-03 }}</ref> in 1950 and is especially useful in areas exposed for less than 1000 years. Growth is greatest in the first 20 to 100 years with 15–50&nbsp;mm growth per year and less in the following years with average growth of 2–4&nbsp;mm per year.<ref>{{cite book |url=https://books.google.com/books?id=xASdKCoT6McC&q=lichenometry&pg=PA562 |last=Schaetzl Randall |first=J |author2=Sharon Anderson |year=2005 |title=Soils Genesis & Geomorphology |publisher=Cambridge University Press |page=562 |isbn=978-0521812016}}</ref>

The difficulty of giving a definition applicable to every known lichen has been debated since lichenologists first recognised the dual nature of lichens. In 1982 the [[International Association for Lichenology]] convened a meeting to adopt a single definition of lichen drawing on the proposals of a committee. The chairman of this committee was the renowned researcher [[Vernon Ahmadjian]]. The definition finally adopted was that lichen could be considered as the association between a fungus and a photosynthetic symbiont resulting in a thallus of specific structure.<ref name="Hawksworth 1989">David L. Hawksworth (1989) "Interactions Fungus and Alga in Lichen Symbiosis liquenoides" ''Annals of the Botanical Garden of Madrid'' (46).</ref>

Such a simple [[A priori and a posteriori|a priori]] definition soon brought criticism from various lichenologists and there soon emerged reviews and suggestions for amendments. For example, [[David L. Hawksworth]] considered the definition imperfect because it is impossible to determine which one thallus is of a specific structure since thalli changed depending upon the substrate and conditions in which they developed. This researcher represents one of the main trends among lichenologists who consider it impossible to give a single definition to lichens since they are a unique type of organism.<ref name="Hawksworth 1989"/>

Today studies in lichenology are not restricted to the description and taxonomy of lichens but have application in various scientific fields. Especially important are studies on [[environmental quality]] that are made through the interaction of lichens with their environment. Lichen is extremely sensitive to various air pollutants, especially to [[sulphur dioxide]], which causes [[acid rain]] and prevents water absorption. [[File:Merezhkovsky K S.jpg|thumb|K S Merezhkovsky Russian Lichenologist (1855–1921)]]