Outline of lichens

• Lichen anatomy and physiology
• Lichen morphology – a lichen's appearance is very different from that of its individual partners[7]

• Apoplast – the symbiotic interface zone, outside the cell membranes or walls of the mycobiont and photobiont[8]
• Ascocarp – the fruiting body of a lichen, which contains the asci[9]

• Ascus (plural asci) – a sexual, fungal spore-bearing structure, typically sac-like[10]
• Ascospore – a fungal spore, the product of meiosis, produced in an ascus[11]

• Epispore – a transparent bag-like outer covering on some spores,[12] which helps to determine spore shape[13]

• Cephalodium (plural cephalodia) – a gall-like structure that contains cyanobacteria[14]
• Hypha (plural 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[15]

• Haustorium (plural haustoria) – a root-like structure which allows the fungal partner to extract nutrients from the photosynthetic partner[12]

• Pycnidium (plural pycnidia) – a flask-shaped, asexual fruiting body possessed by some lichens[16]

• Conidium (plural conidia) – an asexual fungal spore produced in pycnidia by some lichens[17]

• Rhizine – a root-like structure that anchors a lichen to the substrate on which it grows[18]
• Soralium (plural soralia) – a localized region or structure, typically a crack or pore, containing soredium[19]

• Soredium (plural soredia) – asexual reproductive propagules composed of loose aggregates of fungal hyphae and photobiont cells, produced in soralia[19]

• Thallus (plural thalli) – the vegetative body of a lichen, made up of both mycobiont and photobiont components[20]

• Cortex – the lichen's outer layer(s), made up of tightly woven fungal filaments[21]
• Isidium (plural isidia) – outgrowths of the thallus which contain photobiont cells and provide means of vegetative reproduction for some lichens[22]
• Medulla – a loose layer of interwoven fungal hyphae within the thallus[23]
• Podetium (plural podetia) – an upright secondary thallus, which serves as the fruiting structure of Cladonia species[24]

Lichens with a cyanobacteria as the photosynthetic partner, like this Peltigera collina, can fix nitrogen.[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[26]
• 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
• Sexual reproduction in lichens – most lichens reproduce sexually using ascospores, which means they have to acquire their photobiont partners somehow after germinating[27]
• Lichens and nitrogen cycling – some lichens (in particular those with cyanobacteria as a photobiont) can fix nitrogen[25]
• Lichen biogeography – the study of the current distribution of extant lichens and the reasons for those distributions[28]
• Lichen resynthesis – lichens can be artificially "recreated" by combining partners in a lab[29]
• Lichens and pedogenesis – lichens contribute to the formation of soil by breaking down rock[30]
  • 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[31]
• Photosynthesis in lichens

Chaenotheca brunneola falls into Coniocybomycetes, a small fungal class which contains only a handful of lichen species.[32]

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, 38 orders, 119 families, and around 1,000 genera.[32][33]

• Ascolichen – a lichen whose fungal partner is a member of the Ascomycota, one of the two main fungal divisions[34]
• 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[35]

Lichens fall into eight fungal classes and several subclasses:[36]

Lecidella elaeochroma is a member of Lecanorales, the fungal order which contains the greatest number of lichen species.[36]

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.[36] Updated in 2020.[32]

They fall into almost 120 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.[33] Updated in 2020.[32]

Extant lichens are found in around 1000 genera. These were listed in Lücking, Hodkinson and Leavitt's 2016 treatise on the classification of lichenized fungi, except where otherwise noted.[33]

About 20,000 species of lichen have been described, and taxonomists estimate that the number of as yet undescribed species may be as high as 8,000 more.[54]

Xanthoria parietina has the leafy-looking growth of a foliose lichen.[55]

Lichen growth forms – These vary depending on the species:

• Byssoid – wispy, with the appearance of teased wool[56]
• Crustose – paint-like appearance that adheres tightly to the underlying substrate[57]
  • Areolate – crustose, but divided into rounded or polygonal pieces by means of cracks[58]
  • Calicioid – crustose growth with small fruiting bodies which resemble sewing pins[59]
  • Placodioid – crustose in the centre and lobed at the periphery[58]
• Filamentous – thin, threadlike growth, often with a matted appearance[60]
• Foliose – flattened, leafy appearance[58]
• Fruticose – shrubby, bush-like or coral-like appearance[58]
• Gelatinous – jelly-like interior, due to presence of cyanobacteria[61]
• Leprose – powdery or granular appearance[58]
• Squamulose – scaly, sometimes leafy appearance; can resemble a foliose lichen but usually has no outer cortex[62]
  • Cladoniform – squamulose, but with fruticose podetia[63]

Saxicolous lichens are those which grow on stone.[64]

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

• Bryophilous lichen – on mosses or liverworts[64]
  • Hepaticolous lichen – on liverworts[65]
  • Muscicolous lichen – on mosses[66]
• Corticolous lichen – on bark[64]
  • Ramicolous lichen – on twigs[66]
• Foliicolous lichen – on plant leaves[64]
  • Epiphyllous lichen – on the upper surface of a leaf[67]
  • Hypophyllous lichen – on the lower surface of a leaf[67]
• Lichenicolous lichen – on other lichens[64]
• Lignicolous lichen – on wood[64]
• Omnicolous lichen – on various different substrates, including manmade structures[66]
• Plasticolous lichen – on plastic[68]
• Saxicolous lichen – on stone[64]
• Terricolous lichen – on soil[66]
• Vagrant lichen – loose, on no substrate[69]

• Lichens of Madagascar
• Lichens in Namibia

• List of lichens of Sri Lanka

• List of lichens of Western Australia

• List of lichens of Sweden

• 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.)

• American Bryological and Lichenological Society (ABLS)

• The Bryologist – peer-reviewed journal published by ABLS

• Australasian Lichen Society

• Australasian Lichenology – official publication of the Australasian Lichen Society

• British Lichen Society (BLS)

• The Lichenologist – peer-reviewed journal published by the BLS

• 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

• Indian Lichenological Society
• International Association for Lichenology (IAL)
• Nordic Bryological Society

• 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