The following outline provides an overview of and topical guide to lichens.
Lichen – composite organism made up of multiple species – a fungal partner, one or more photosynthetic partners, which can be either green algae or cyanobacteria, and, in at least 52 genera of lichens, a yeast.[1] In American English, "lichen" is pronounced the same as the verb "liken" (/ˈlaɪkən/). In British English, both this pronunciation and one rhyming with "kitchen" (/ˈlɪtʃən/) are used.[2]
Composite organism – a symbiotic life form composed of multiple partners from different biological domains, families and kingdoms, and from different phyla, classes and divisions within those domains and kingdoms. In the case of lichens, a fungal partner (the mycobiont) combines with one or more photosynthetic partner(s) (the photobiont) as well as (in some cases) a yeast.
Eukaryote (domain) – organisms with a cell nucleus within a nuclear envelope; both the mycobiont and any algal partners fall into this domain.[3]
Fungi (kingdom) – the fungal partner and any yeast partner fall into this kingdom.[1]
Epispore – a transparent bag-like outer covering on some spores,[9] which helps to determine spore shape.[14]
Cephalodium (pl. cephalodia) – a gall-like structure that contains cyanobacteria[15]
Hypha (pl. hyphae) – a long, branching, thread-like structure composed of one or more fungal cells, which typically makes up a large part of lichens; hyphae are densely compacted in the cortex and more loosely interwoven in the medulla.[16]
Pycnidium (pl. pycnidia) – a flask-shaped, asexual fruiting body possessed by some lichens.[17]
Conidium (pl. conidia) – an asexual fungal spore produced in pycnidia by some lichens.[18]
Rhizine – a root-like structure that anchors a lichen to the substrate on which it grows.[19]
Soralium (pl. soralia) – a localized region or structure, typically a crack or pore, containing soredium.[20]
Soredium (pl. soredia) – asexual reproductive propagules composed of loose clumps of fungal hyphae and photobiont cells, produced in soralia.[20]
Thallus (pl. thalli) – the vegetative body of a lichen, made up of both mycobiont and photobiont components.[21]
Cortex – the lichen's outer layer(s), made up of tightly woven fungal filaments.[22]
Isidium (pl. isidia) – outgrowths of the thallus which contain photobiont cells and provide means of vegetative reproduction for some lichens.[23]
Medulla – a loose layer of interwoven fungal hyphae within the thallus.[24]
Podetium (pl. podetia) – an upright secondary thallus, which supports the fruiting bodies of Cladonia species.[25]
Symbiosis in lichens – the relationship between the lichen partners can be complicated; while generally mutualistic, sometimes it is not. Recent research also shows other partners, including bacteria and "accessory" fungi, may be involved.[27]
Asexual reproduction in lichens – many lichens reproduce asexually, using one or more of various methods which allow the dispersal of bundles of both fungal hyphae and photobionts.[28]
Biological soil crust – lichens are among the common dominant biota in biocrusts, one of the world's largest environmental community types in terms of area covered.[33]
Basidiolichen – a lichen whose fungal partner is a member of the Basidiomycota, the other of the two main fungal divisions; these are far fewer in occurrence than ascolichens.[37]
They are split across nearly 40 orders. Those which cannot be assigned to a particular order are assigned instead to "incertae sedis" within the appropriate class. These orders were listed in Lücking, Hodkinson and Leavitt's 2016 treatise on the classification of lichenized fungi, except where otherwise noted,[38] with orders updated in 2021.[34]
They fall into 117 families. Those which cannot be assigned to a particular family are assigned instead to "incertae sedis" within the appropriate order. These were listed in Lücking, Hodkinson and Leavitt's 2016 treatise on the classification of lichenized fungi, except where otherwise noted;[35] families were updated in 2021.[34]
Extant lichens are found in more than 1000 genera. These were listed in Lücking, Hodkinson and Leavitt's 2016 treatise on the classification of lichenized fungi, except where otherwise noted.[35]
In 2009, taxonomists estimated that the total number of lichen species (including those yet undiscovered) might be as high as 28,000.[98] By 2016, 19,387 species of lichens had been described and widely accepted.[99]
Lichen product – organic products, known as secondary metabolites, produced by lichens; these provide a variety of protections for the lichen – from microbes, viruses, herbivores, radiation, oxidants and more.[118]
Lichenometry – a process where measuring the growth of a lichen colony over time can be used to estimate the minimum age of the substrate on which it is growing.[123]
Cáceres, Marcela Eugenia da Silva; Aptroot, André; Mendonça, Cléverton Oliveira; Santos, Lidiane Alves; Lücking, Robert (2017). "Sprucidea, a further new genus of rain forest lichens in the family Malmideaceae (Ascomycota)". Bryologist. 120 (2): 202–211. doi:10.1639/0007-2745-120.2.202. S2CID90645323.
Díaz-Escandón, David; Hawksworth, David L.; Powell, Mark; Resl, Philipp; Spribille, Toby (February 2021). "The British chalk specialist Lecidea lichenicola auct. revealed as a new genus of Lichinomycetes". Fungal Biology. 125 (7): 495–504. Bibcode:2021FunB..125..495D. doi:10.1016/j.funbio.2021.01.007. PMID34140146. S2CID234008195.
Divakar, Pradeep K.; Crespo, Ana; Kraichak, Ekaphan; Leavitt, Steven D.; Singh, Garima; Schmitt, Imke; Lumbsch, H. Thorsten (2017). "Using a temporal phylogenetic method to harmonize family- and genus-level classification in the largest clade of lichen-forming fungi". Fungal Diversity. 84: 101–117. doi:10.1007/s13225-017-0379-z. S2CID40674310.
Dobson, Frank S. (2011). Lichens: An Illustrated Guide to the British and Irish Species. Slough, UK: Richmond Publishing Co. ISBN978-0-85546-316-8.
Ertz, Damien; Søchting, Ulrik; Gadea, Alice; Charrier, Maryvonne; Poulsen, Roar S. (2017). "Ducatina umbilicata gen. et sp. nov., a remarkable Trapeliaceae from the subantarctic islands in the Indian Ocean". The Lichenologist. 49 (2): 127–140. doi:10.1017/s0024282916000700. S2CID90273663.
Ertz, Damien; Sanderson, Neil; Łubek, Anna; Kukwa, Martin (March 2018). "Two new species of Arthoniaceae from old-growth European forests, Arthonia thoriana and Inoderma sorediatum, and a new genus for Schismatomma niveum". The Lichenologist. 50 (2): 161–172. doi:10.1017/S0024282917000688.
Etayo, Javier (2017). Hongos liquenícolas de Ecuador(PDF). Opera Lilloana (in Spanish). San Miguel de Tucumán, Argentina: Fundación Miguel Lillo.
Favor, Lesli J. (2005). Eukaryotic and Prokaryotic Cell Structures: Understanding Cells with and Without a Nucleus. New York: Rosen Publishing Group. ISBN978-1-4042-0323-5.
Galloway, D. J. (2012). "Lichen biogeography". In Nash III, Thomas H. (ed.). Lichen Biology. Cambridge UK: Cambridge University Press. pp. 315–335. ISBN978-0-521-69216-8.
"Glossary of Terms". The British Lichen Society. 2022b. Retrieved 18 August 2022.
Goga, Michal; Elečko, Ján; Marcinčinová, Margaréta; Ručová, Dajana; Bačkorová, Miriam; Bačkor, Martin (2018). "Lichen Metabolites: An Overview of Some Secondary Metabolites and Their Biological Potential". In Merillon, J. M.; Ramawat, K. (eds.). Bioactive Molecules in Food. Reference Series in Phytochemistry. Springer, Cham. pp. 1–36. doi:10.1007/978-3-319-76887-8_57-1. ISBN978-3-319-76887-8.
Green, T. G. Allen; Pintado, Ana; Raggio, Jose; Sancho, Leopoldo Garcia (May 2018). "The lifestyle of lichens in soil crusts". The Lichenologist. 50 (3): 397–410. doi:10.1017/S0024282918000130. S2CID90874682.
Grube, Martin (October 2018). "Staurospora, a new genus for a unique species with spherical ascospores in Arthoniaceae". Herzogia. 31 (p1): 695–699. doi:10.13158/heia.31.1.2018.695. S2CID198159947.
Kantvilas, Gintaras; Wedin, Mats; Svensson, Måns (September 2021). "Australidea (Malmideaceae, Lecanorales), a new genus of lecideoid lichens, with notes on the genus Malcolmiella". The Lichenologist. 53 (5): 395–407. doi:10.1017/s0024282921000311. S2CID238638591.
Kraichak, E.; Huang, J.P.; Nelsen, M.; Leavitt, S.D.; Lumbsch, H.T. (12 September 2018). "Nomenclatural novelties"(PDF). Index Fungorum. 375: 1. ISSN2049-2375.
Kistenich, Sonja; Timdal, Einar; Bendiksby, Mika; Ekman, Stefan (2018). "Molecular systematics and character evolution in the lichen family Ramalinaceae (Ascomycota: Lecanorales)". Taxon. 67 (5): 871–904. doi:10.12705/675.1. hdl:10852/67955.
Laundon, Jack R. (1986). Lichens. Shire Natural History series. Princes Risborough: Shire Publications. ISBN978-0-85263-811-8.
Lendemer, James C.; Buck, William R.; Harris, Richard C. (September 2016). "Two new host-specific hepaticolous species of Catinaria (Ramalinaceae)". The Lichenologist. 48 (5): 441–449. doi:10.1017/S0024282916000438. S2CID89433929.
Lendemer, James C.; Stone, Heather B.; Tripp, Erin A. (2017). "Taxonomic delimitation of the rare, eastern North American endemic lichen Santessoniella crossophylla (Pannariaceae)". The Journal of the Torrey Botanical Society. 144 (4): 459–468. doi:10.3159/torrey-d-16-00009.1. JSTOR26305705. S2CID90392751.
Lepp, Heino (2014). "Basidiolichens". Australian Lichens. Australian National Herbarium and Australian National Botanic Gardens. Retrieved 20 August 2022.
Lücking, Robert (May 1998). "'Plasticolous' Lichens in a Tropical Rain Forest at La Selva Biological Station, Costa Rica". The Lichenologist. 30 (3): 287–291. doi:10.1006/lich.1998.0124. S2CID250348579.
Lücking, Robert; Hodkinson, Brendan P.; Leavitt, Steven D. (Winter 2016). "The 2016 classification of lichenized fungi in the Ascomycota and Basidiomycota–Approaching one thousand genera". The Bryologist. 119 (4): 361–416. doi:10.1639/0007-2745-119.4.361. JSTOR44250015. S2CID90258634.
Lücking, Robert; Hodkinson, Brendan P.; Leavitt, Steven D. (2017). "Corrections and amendments to the 2016 classification of lichenized fungi in the Ascomycota and Basidiomycota". The Bryologist. 120 (1): 58–69. doi:10.1639/0007-2745-120.1.058. JSTOR44820821. S2CID90363578.
Lücking, Robert; Kalb, Klause (2018). "Formal instatement of Allographa (Graphidaceae): how to deal with a hyperdiverse genus complex with cryptic differentiation and paucity of molecular data". Herzogia. 31 (p1): 535–561. doi:10.13158/heia.31.1.2018.535. S2CID217375498.
Lücking, Robert; Rivas-Plata, E; Chavez, JL; Umaña, L; Sipman, HJM (2009). "How many tropical lichens are there… really?". Bibliotheca Lichenologica. 100: 399–418.
Schultz, Matthias; Zedda, Luciana; Rambold, Gerhard (2009). "New records of lichen taxa from Namibia and South Africa Bibliotheca Lichenologica"(PDF). In Aptroot, André; Seaward, Mark R.D.; Sparrius, Laurens B. (eds.). Biodiversity and ecology of lichens – Liber Amicorum Harrie Sipman. Vol. 99. Berlin and Stuttgart: J. Cramer. pp. 315–334.
Silverstein, Alvin; Silverstein, Virginia B.; Silverstein, Robert A. (1996). Fungi. New York: Twenty-First Century Books. ISBN978-0-8050-3520-9.
Smith, C. W.; Aptroot, A.; Coppins, B. J.; Fletcher, A.; Gilbert, O. L.; James, P. W.; Wolseley, P. A., eds. (2009). The Lichens of Great Britain and Ireland. London: The British Lichen Society. ISBN978-0-9540418-8-5.
Smith, Hayden B.; Dal Grande, Francesco; Muggia, Lucia; Keuler, Rachel; Divakar, Pradeep K.; Grewe, Felix; Schmitt, Imke; Lumbsch, H. Thorsten; Leavitt, Steven D. (November 2020). "Metagenomic data reveal diverse fungal and algal communities associated with the lichen symbiosis". Symbiosis. 82 (1–2): 133–147. Bibcode:2020Symbi..82..133S. doi:10.1007/s13199-020-00699-4. hdl:11577/3440801. S2CID214724803.
Sobreira, Priscylla Nayara Bezerra; Cáceres, Marcela Eugenia Da Silva; Maia, Leonor Costa; Lücking, Robert (July 2018). "Flabelloporina, a new genus in the Porinaceae (Ascomycota, Ostropales), with the first record of F. squamulifera from Brazil". Phytotaxa. 538 (1): 67–75. doi:10.11646/phytotaxa.358.1.4. S2CID89707839.
Upreti, Dalip K.; Rai, Himanshu, eds. (2013). Terricolous Lichens in India. Vol. 1: Diversity Patterns and Distribution Ecology. New York: Springer. ISBN978-1-4614-8736-4.
Wilk, Karina; Pabijan, Maciej; Saługa, Marta; Gaya, Ester; Lücking, Robert (2021). "Phylogenetic revision of South American Teloschistaceae (lichenized Ascomycota, Teloschistales) reveals three new genera and species". Mycologia. 113 (2): 278–299. doi:10.1080/00275514.2020.1830672. PMID33428561. S2CID231586897.