Biology:Outline of lichens

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Short description: Overview of and topical guide to lichens

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An intricately branched, pale green lichen hangs from a branch.
Usnea filipendula – one of about 20,000 described species of lichen

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]


What type of thing is a lichen?

A lichen can be described as all of the following:

  • Life form – an entity that is alive.
  • Composite organism – a symbiotic life form composed of multiple partners from different biological domains, families and kingdoms, and into 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]
  • For the biological classes and families these fungi belong to, see below.
  • Prokaryote (domain) – organisms without a cell nucleus; any cyanobacterial partner falls into this domain.[3]

Nature of lichens

Section labeled "a" is grey, dotted with hundreds of small white circles. Section labeled "b" has grey strands surrounding numerous green circles. Section labeled "c" has loosely tangled grey strands with much open space between them. Section labeled "d" mirrors section labeled "a". In the section labeled "e", the structure in section "d" descends to two points - again grey with many white circles
Schematic cross section of foliose lichen:
(a) The cortex is the outer layer of tightly woven fungal filaments (hyphae)
(b) This photobiont layer has photosynthesizing green algae
(c) Loosely packed hyphae in the medulla
(d) A tightly woven lower cortex
(e) Anchoring hyphae called rhizines, where the fungus attaches to the substrate

Morphology

  • Lichen anatomy and physiology
  • Apoplast – the symbiotic interface zone between the mycobiont and photobiont, outside the cell membranes or walls of both.[8]
  • Haustorium (pl. haustoria) – a root-like structure which allows the fungal partner to extract nutrients from its photosynthetic partner(s).[9]
  • Lichen morphology – a lichen's external appearance and structures are very different than those of its individual partners.[10]
  • Ascocarp – the fruiting body of a lichen, which contains the asci.[11]
  • Ascus (pl. asci) – a sexual, fungal spore-bearing structure, typically sac-like in shape.[12]
  • Ascospore – a fungal spore, the product of meiosis, produced in an ascus.[13]
  • 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]

Ecology

A leafy, dark bronze lichen with wavy, white-tipped edges on a piece of bark
Lichens with a cyanobacteria as the photosynthetic partner, like this Peltigera collina, can fix nitrogen.[26]
  • 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]
  • Sexual reproduction in lichens – most lichens reproduce sexually using ascospores, which means they have to acquire their photobiont partners somehow after germinating.[29]
  • Lichens and nitrogen cycling – some lichens (in particular those with cyanobacteria as a photobiont) can fix nitrogen.[26]
  • Lichen biogeography – the study of the current distribution of extant lichens and the reasons for those distributions.[30]
  • Lichen resynthesis – lichens can be artificially "recreated" by combining partners in a lab.[31]
  • Lichens and pedogenesis – lichens contribute to the formation of soil by breaking down rock.[32]
    • 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]
  • Photosynthesis in lichens

Types of lichens

Lichen lists

Lichen taxonomical classifications

Several small brown balls rest atop black stalks rising from a bit of wood.
Chaenotheca brunneola falls into Coniocybomycetes, a small fungal class which contains only a handful of lichen species.[34]

Lichen systematics – Although they are composite organisms, lichens have traditionally been classified on the basis of their fungal partner. These span eight different biological classes, 39 orders, 117 families, and around 1,000 genera.[34][35]

Classes

Lichens fall into eight fungal classes and several subclasses:[38]

  1. Agaricomycetes
    1. Agaricomycetidae
  2. Arthoniomycetes
  3. Coniocybomycetes
  4. Dothideomycetes
    1. Dothideomycetidae
  5. Eurotiomycetes
    1. Chaetothyriomycetidae
  6. Lecanoromycetes
    1. Acarosporomycetidae
    2. Lecanoromycetidae
    3. Ostropomycetidae
  7. Lichinomycetes
  8. Sordariomycetes
    1. Sordariomycetidae

Orders

A thick branch covered with a white crust, marked by black spots and thin black lines.
Lecidella elaeochroma is a member of Lecanorales, the fungal order which contains the greatest number of lichen species.[38]

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]

  1. Acarosporales
  2. Agaricales
  3. Arthoniales
  4. Atheliales
  5. Baeomycetales
  6. Caliciales
  7. Candelariales
  8. Cantharellales
  9. Capnodiales
  10. Chaetothyriales
  11. Collemopsidiales
  12. Coniocybales
  13. Corticiales
  14. Eremithallales
  15. Lecanorales
  16. Lecideales
  17. Lepidostromatales
  18. Leprocaulales
  19. Lichinales
  20. Monoblastiales
  21. Odontotrematales
  22. Ostropales
  23. Peltigerales
  24. Pertusariales
  25. Phaeomoniellales
  26. Pleosporales
  27. Pyrenulales
  28. Rhizocarpales
  29. Sarrameanales
  30. Schaereriales[39][40]
  31. Strigulales
  32. Teloschistales
  33. Thelenellales[39][40]
  34. Thelocarpales
  35. Trypetheliales
  36. Umbilicariales
  37. Verrucariales
  38. Vezdaeales
  39. Xylariales

Families

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]


Genera

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]


Species

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]

Lichens, by growth form

Stick covered with flat, yellowy-green, wavy-edged lichen speckled with raised orange spots
Xanthoria parietina has the leafy-looking growth of a foliose lichen.[100]

Lichen growth forms – These vary depending on the species:

  • Crustose – paint-like appearance that adheres tightly to the underlying substrate.[101]
    • Areolate – crustose, but divided into rounded or polygonal pieces by means of cracks.[102]
    • Leprose – powdery or granular appearance.[102]
    • Calicioid – crustose growth with small fruiting bodies which resemble sewing pins.[103]
    • Placodioid – crustose in the centre and lobed at the periphery.[102]
  • Foliose – flattened, leafy appearance.[102]
  • Fruticose – shrubby, bush-like or coral-like appearance.[102]
    • Byssoid – wispy, with the appearance of teased wool.[104]
    • Filamentous – thin, threadlike growth, often with a matted appearance.[105]
  • Gelatinous – jelly-like interior, due to presence of cyanobacteria.[106]
  • Squamulose – scaly, sometimes leafy appearance; can resemble a foliose lichen but usually has no outer cortex.[107]
    • Cladoniform – squamulose, but with fruticose podetia.[108]

Lichens, by substrate

Photo of stony ground with one large rock covered in a multitude of lichens of different sizes, shapes and colours
Saxicolous lichens are those which grow on stone.[109]

Lichens can be classified by the substrate on which they grow:

  • Bryophilous lichen – on mosses or liverworts.[109]
    • Hepaticolous lichen – on liverworts.[110]
    • Muscicolous lichen – on mosses.[111]
  • Corticolous lichen – on bark.[109]
    • Ramicolous lichen – on twigs.[111]
  • Foliicolous lichen – on plant leaves.[109]
    • Epiphyllous lichen – on the upper surface of a leaf.[112]
    • Hypophyllous lichen – on the lower surface of a leaf.[112]
  • Lichenicolous lichen – on other lichens.[109]
  • Lignicolous lichen – on wood stripped of bark.[109]
  • Omnicolous lichen – on a variety of substrates.[111]
  • Plasticolous lichen – on plastic.[113]
  • Saxicolous lichen – on stone.[109]
    • Endolithic lichen – within stone.[22]
  • Terricolous lichen – on soil.[111]
  • Vagrant lichen – loose, on no substrate.[114]

Lichens, by region

Photo of sandy ground with patches of flat brown and bright orange ball-shaped lichens
Namibia's vast deserts, which hold many species of lichen, remain largely unsurveyed.[115]

Africa

  • List of lichens of Madagascar
  • List of lichens of Namibia

Antarctica

Asia

  • List of lichens of Sri Lanka

Australia

  • List of lichens of Western Australia

Europe

  • List of lichens of Sweden

North America

  • List of lichens of Maryland
    • List of lichens of Soldiers Delight – lichens of a nature reserve in Maryland
  • List of lichen species of Montana
  • Lichens of the Sierra Nevada (U.S.)

Oceania

Pacific

South America

Photobiont

Picture through microscope of four algal cells: round with clear edges and bright green centres
The photobiont in most lichens is a green alga, particularly those from the genus Trebouxia.[6]

Photobiont – the photosynthetic partner in a lichen.[116]

  • Cyanolichen – a lichen with a cyanobacteria photobiont.[117]
  • List of lichen photobionts

Lichen metabolites

Further information: Biology:Secondary metabolite

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]

  • List of lichen products
Four photos showing a leafy dark green lichen; the top two are virtually identical, though one photo is labeled C (calcium hypochlorite or sodium hypochlorite) and K (potassium hydroxide) and the other labeled C and KC (K followed immediately by C). The bottom two show a colour change; where the medulla has been exposed, its colour changes to pinkish-red when exposed to C and KC.
Chemical spot tests on the foliose lichen Punctelia borreri showing thallus (top) and medulla (bottom). The pinkish-red colour change of the medulla in the C and KC tests indicate the presence of gyrophoric acid, a chemical feature that helps to distinguish this lichen from similar species in the same genus.[119]

Study of lichens

Lichenology – the study of lichens.[120]

  • Acharius Medal – awarded for lifetime achievement in lichenology.[121]
  • Evolution of lichens – lichenization of fungi has occurred multiple times, and several pathways towards acquiring photobionts have arisen.
    • List of fossil lichens
  • Exsiccata (plural exsiccatae) – a published set of preserved specimens, numbered and distributed with printed labels.[122]
  • History of lichenology
  • 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]
  • Spot test (lichen) – chemical tests used to aid in species identification.[124]

Threats

  • Lichenicolous fungus – parasitic fungus that uses lichens as a host.[125]
  • List of lichenicolous fungi
  • Lichens as bioindicators – lichens are sensitive to various pollutants and can be thus be used as bioindicators.[126]
  • Lichens and air pollution – many lichens are sensitive to various forms of air pollution.[127]
  • Lichens and climate change – the inability of algae to quickly evolve means that climate change may adversely impact lichens.[128]

Lichens in culture

Two black loaves sit on a plate with knife and fork beside them.
Two baked loaves of Bryoria fremontii, an important traditional food for some First Nations people[129]
  • Cultural depictions of lichens
  • Trouble with Lichen – science fiction novel by John Wyndham in which lichens play a major role.[130]
  • Edible lichen – some lichens have traditionally been used as food.[131]
  • Ethnolichenology – a branch of ethnobotany that studies human usage of lichens.[132]

Lichen organizations

  • Australasian Lichen Society
  • Australasian Lichenology – official publication of the Australasian Lichen Society.
  • Bryological and Lichenological Association for Central Europe (BLAM)
  • Herzogia – peer-reviewed journal published by BLAM.
  • Bryological and Lichenological Working Group (Bryologische en Lichenologische Werkgroep, BLWG)
  • Buxbaumiella – peer-reviewed journal published by BLWG.
  • Dutch Bryological and Lichenological Society
  • Lindbergia – peer-reviewed journal co-published by the Dutch Bryological and Lichenological Society and the Nordic Bryological Society.

Independent lichenological journals

  • Asian Journal of Mycology – an international peer-reviewed journal published by Mae Fah Luang University in Thailand.
  • Bibliotheca Lichenologica – scientific monographs on lichens and mosses.
  • Hattoria – an international, peer-reviewed journal issued by Hattori Botanical Laboratory.
  • International Journal of Mycology and Lichenology

See also

Citations

  1. ↑ 1.0 1.1 Van Hoose 2021.
  2. ↑ Cambridge Dictionary.
  3. ↑ 3.0 3.1 Favor 2005, p. 5.
  4. ↑ Laundon 1986, p. 3.
  5. ↑ Li et al. 2021, p. evab101.
  6. ↑ 6.0 6.1 6.2 Purvis 2000, p. 9.
  7. ↑ 7.0 7.1 Laundon 1986, p. 2.
  8. ↑ Honegger 1998, p. 197.
  9. ↑ 9.0 9.1 Brodo, Sharnoff & Sharnoff 2001, p. 758.
  10. ↑ Baron 1999, p. 14.
  11. ↑ Hawksworth, Sutton & Ainsworth 1983, p. 26.
  12. ↑ Silverstein, Silverstein & Silverstein 1996, p. 32.
  13. ↑ Smith et al. 2009, p. 22.
  14. ↑ Smith et al. 2009, p. 30.
  15. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 756.
  16. ↑ Hale 1983, pp. 3, 6.
  17. ↑ Smith et al. 2009, p. 36.
  18. ↑ Smith et al. 2009, p. 24.
  19. ↑ Hawksworth, Sutton & Ainsworth 1983, p. 330.
  20. ↑ 20.0 20.1 Smith et al. 2009, p. 38.
  21. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 763.
  22. ↑ 22.0 22.1 Brodo, Sharnoff & Sharnoff 2001, p. 757.
  23. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 759.
  24. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 760.
  25. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 761.
  26. ↑ 26.0 26.1 Henriksson & Simu 1971, p. 119.
  27. ↑ Smith et al. 2020, p. 134.
  28. ↑ Bowler & Rundel 1975, p. 328.
  29. ↑ Bowler & Rundel 1975, p. 326–327.
  30. ↑ Galloway 2012, p. 315.
  31. ↑ Zakeri et al. 2022, p. 80.
  32. ↑ Chen, Blume & Beyer 2000, p. 124.
  33. ↑ Green et al. 2018, p. 397.
  34. ↑ 34.0 34.1 34.2 34.3 Wijayawardene et al. 2022.
  35. ↑ 35.0 35.1 35.2 Lücking, Hodkinson & Leavitt 2016, p. 377–400.
  36. ↑ Bendre 2010, p. 131.
  37. ↑ Lepp 2014.
  38. ↑ 38.0 38.1 38.2 Lücking, Hodkinson & Leavitt 2016, p. 371.
  39. ↑ 39.0 39.1 Kraichak et al. 2018a.
  40. ↑ 40.0 40.1 Kraichak et al. 2018b.
  41. ↑ 41.0 41.1 41.2 41.3 Wijayawardene et al. 2022, p. 162.
  42. ↑ 42.00 42.01 42.02 42.03 42.04 42.05 42.06 42.07 42.08 42.09 42.10 Lücking, Hodkinson & Leavitt 2017, p. 58.
  43. ↑ Gamundí & Spinedi 1985, p. 112.
  44. ↑ Jiang et al. 2020, p. 11.
  45. ↑ 45.0 45.1 Wijayawardene et al. 2022, p. 124.
  46. ↑ Lendemer, Harris & Ruiz 2016, p. 26.
  47. ↑ Lücking & Kalb 2018, p. 353.
  48. ↑ Wilk et al. 2021, p. 289.
  49. ↑ Aptroot, Sparrius & Alvarado 2018, p. 12.
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  51. ↑ Spribille et al. 2020, p. 85.
  52. ↑ Kantvilas, Wedin & Svensson 2021, p. 400.
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  55. ↑ Diederich & Ertz 2020, p. 22.
  56. ↑ Kistenich et al. 2018, p. 871.
  57. ↑ Fryday et al. 2020, p. 473.
  58. ↑ Wilk et al. 2021, p. 293.
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  61. ↑ 61.0 61.1 Wijayawardene et al. 2022, p. 156.
  62. ↑ 62.0 62.1 62.2 Divakar et al. 2017, p. 109.
  63. ↑ Ertz et al. 2017, p. 131.
  64. ↑ Wijayawardene et al. 2022, p. 159.
  65. ↑ Kondratyuk et al. 2017, p. 86.
  66. ↑ Simon et al. 2020, p. 82.
  67. ↑ Sobreira et al. 2018, p. 67.
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  69. ↑ Kondratyuk et al. 2017, p. 90.
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  72. ↑ Grube, Matzer & Hafellner 1995, p. 28.
  73. ↑ 73.0 73.1 Wijayawardene et al. 2022, p. 89.
  74. ↑ Kondratyuk et al. 2018, p. 97.
  75. ↑ Kondratyuk et al. 2017, p. 105.
  76. ↑ Wijayawardene et al. 2022, p. 98.
  77. ↑ Sodamuk et al. 2017, p. 15.
  78. ↑ Kondratyuk et al. 2021, p. 372.
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  80. ↑ 80.0 80.1 Wijayawardene et al. 2022, p. 149.
  81. ↑ Kalb & Aptroot 2021, p. 5.
  82. ↑ Kondratyuk et al. 2015, p. 328.
  83. ↑ Bungartz, Søchting & Arup 2021.
  84. ↑ Kondratyuk et al. 2017, p. 112.
  85. ↑ Etayo 2017, p. 335.
  86. ↑ Wijayawardene et al. 2022, p. 160.
  87. ↑ Davydov et al. 2021, p. 245.
  88. ↑ Kondratyuk et al. 2018, p. 107.
  89. ↑ Lendemer, Stone & Tripp 2017, p. 459.
  90. ↑ Ertz et al. 2018, p. 170.
  91. ↑ Cáceres et al. 2017, p. 206.
  92. ↑ Wijayawardene et al. 2022, p. 38.
  93. ↑ Grube 2018, p. 695.
  94. ↑ Jiang et al. 2020, p. 1.
  95. ↑ Kondratyuk et al. 2018, p. 24.
  96. ↑ Kondratyuk et al. 2016, p. 104.
  97. ↑ Díaz-Escandón et al. 2021, p. 501.
  98. ↑ Lücking et al. 2009, p. 411.
  99. ↑ Lücking, Hodkinson & Leavitt 2016, p. 370.
  100. ↑ Dobson 2011, p. 470.
  101. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 16.
  102. ↑ 102.0 102.1 102.2 102.3 102.4 The British Lichen Society 2022a.
  103. ↑ Temu et al. 2019, p. 1.
  104. ↑ Kantvilas 1996, p. 229.
  105. ↑ Dobson 2011, p. 26.
  106. ↑ Sanders 2001, p. 1033.
  107. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 17.
  108. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 18.
  109. ↑ 109.0 109.1 109.2 109.3 109.4 109.5 109.6 The British Lichen Society 2022b.
  110. ↑ Lendemer, Buck & Harris 2016, p. 441.
  111. ↑ 111.0 111.1 111.2 111.3 Upreti & Rai 2013, p. 2.
  112. ↑ 112.0 112.1 Lücking 2008, p. 4.
  113. ↑ Lücking 1998, p. 287.
  114. ↑ Rosentreter 1993, p. 333.
  115. ↑ Schultz, Zedda & Rambold 2009, p. 315.
  116. ↑ Purvis 2000, p. 5.
  117. ↑ Rikkinen 2015, p. 973.
  118. ↑ Goga et al. 2018, p. 1.
  119. ↑ Truong & Clerc 2003, p. 52.
  120. ↑ Merriam-Webster.
  121. ↑ International Association for Lichenology.
  122. ↑ Pfister 1985, p. 1.
  123. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 84.
  124. ↑ Brodo, Sharnoff & Sharnoff 2001, p. 103.
  125. ↑ Lawrey & Diederich 2003, p. 80.
  126. ↑ Nimis, Scheidegger & Wolseley 2002.
  127. ↑ Oliver 2011, p. 1.
  128. ↑ Field Museum 2022.
  129. ↑ Turner 1977, p. 461.
  130. ↑ Penguin Books.
  131. ↑ Ivanova & Ivanov 2009, p. 11.
  132. ↑ Vinayaka & Krishnamurthy 2012, p. 265.

References

External links



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