The following

outline Outline or outlining may refer to: * Outline (list), a document summary, in hierarchical list format * Code folding, a method of hiding or collapsing code or text to see content in outline form * Outline drawing, a sketch depicting the outer edge ...

provides an overview of and topical guide to lichens.

Lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.composite Composite or compositing may refer to: Materials * Composite material, a material that is made from several different substances ** Metal matrix composite, composed of metal and other parts ** Cermet, a composite of ceramic and metallic materials ...

organism made up of multiple species – a

fungal A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

partner, one or more

photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

partners, which can be either

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

, and, in at least 52 genera of lichens, a basidiomycete yeast.

What is a lichen?

A lichen can be described as all of the following: *

Life form Life form (also spelled life-form or lifeform) is an entity that is living, such as plants (flora) and animals (fauna). It is estimated that more than 99% of all species that ever existed on Earth, amounting to over five billion species, are ext ...

– an entity that is alive :* Composite organism –

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

life form composed of multiple partners from different biological domains,

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

and

kingdoms Kingdom commonly refers to: * A monarchy ruled by a king or queen * Kingdom (biology), a category in biological taxonomy Kingdom may also refer to: Arts and media Television * ''Kingdom'' (British TV series), a 2007 British television drama s ...

, and different

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phyl ...

, classes and divisions within those domains and kingdoms ::*

Eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

(domain) – organisms with a

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

within a nuclear envelope :::*

Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

(kingdom) – the fungal partner (known as the

mycobiont A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...

(phylum) and/or

Basidiomycota Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...

(phylum) :::* Chlorophyta (division) – if the photosynthetic partner, or

photobiont A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

::::* Trebouxiophyceae (class) :::::* Trebouxiaceae (family) ::::* Ulvophyceae (class) :::::*

Trentepohliaceae Trentepohliaceae are a family of green algae in the order Trentepohliales Trentepohliales is an order (biology), order of Ulvophyceaen green algae.See the National Center for Biotechnology Information, NCBI]webpage on Trentepohliales Data ext ...

(family) ::*

Prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

(domain) – organisms without a cell nucleus :::*

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

(domain) – if the photobiont is a cyanobacterium ::::*

Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

(phylum)

Nature of lichens

Lichen cross section – heteromeric thallus

Morphology

Lichen anatomy and physiology Lichen anatomy and physiology is very different from the anatomy and physiology of the fungus and/or algae and/or cyanobacteria that make up the lichen when growing apart from the lichen, either naturally, or in culture. The fungal partner is cal ...

Lichen morphology Lichen morphology describes the external appearance and structures of a lichen. These can vary considerably from species to species. Lichen growth forms are used to group lichens by "vegetative" thallus types, and forms of "non-vegetative" rep ...

– a lichen's appearance is very different from that of its individual partners :* Apoplast – the symbiotic interface zone, outside the cell membranes or walls of the mycobiont and photobiont :*

Ascocarp An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are m ...

– the fruiting body of a lichen, which contains the asci ::*

Ascus An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...

(plural ''asci'') – a sexual, fungal spore-bearing structure, typically sac-like ::*

Ascospore An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...

– a fungal spore, the product of

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

, produced in an ascus :::*

Epispore The following is a glossary of terms used in the description of lichens, composite organisms that arise from algae or cyanobacteria living among filaments of multiple fungus species in a mutualistic relationship. Until the end of the 18th ...

– a transparent bag-like outer covering on some spores, which helps to determine spore shape :* Cephalodium (plural ''cephalodia'') – a

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...

-like structure that contains cyanobacteria :*

Hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

(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 ::*

Haustorium In botany and mycology, a haustorium (plural haustoria) is a rootlike structure that grows into or around another structure to absorb water or nutrients. For example, in mistletoe or members of the broomrape family, the structure penetrates t ...

(plural ''haustoria'') – a root-like structure which allows the fungal partner to extract nutrients from the photosynthetic partner :* Pycnidium (plural ''pycnidia'') – a flask-shaped, asexual fruiting body possessed by some lichens ::* Conidium (plural ''conidia'') – an asexual fungal spore produced in pycnidia by some lichens :* Rhizine – a root-like structure that anchors a lichen to the substrate on which it grows :* Soralium (plural ''soralia'') – a localized region or structure, typically a crack or pore, containing soredium ::*

Soredium Soredia are common reproductive structures of lichens. Lichens reproduce asexually by employing simple fragmentation and production of soredia and isidia. Soredia are powdery propagules composed of fungal hyphae wrapped around cyanobacteria o ...

(plural ''soredia'') – asexual reproductive propagules composed of loose aggregates of fungal hyphae and photobiont cells, produced in soralia :*

Thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms wer ...

(plural ''thalli'') – the vegetative body of a lichen, made up of both mycobiont and photobiont components ::* Cortex – the lichen's outer layer(s), made up of tightly woven fungal filaments ::*

Isidium An isidium is a vegetative reproductive structure present in some lichens. Isidia are outgrowths of the thallus surface, and are corticated (i.e., containing the outermost layer of the thallus), usually with a columnar structure, and consisting o ...

(plural ''isidia'') – outgrowths of the thallus which contain photobiont cells and provide means of vegetative reproduction for some lichens ::* Medulla – a loose layer of interwoven fungal hyphae within the thallus ::* Podetium (plural ''podetia'') – an upright secondary thallus, which serves as the fruiting structure of ''Cladonia'' species

Ecology

Symbiosis in lichens Symbiosis in lichens is the mutually helpful symbiotic relationship of green algae and/or blue-green algae (cyanobacteria) living among filaments of a fungus, forming lichen. Living as a symbiont in a lichen appears to be a successful way for a ...

– 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 * 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

ascospore An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...

s, which means they have to acquire their photobiont partners somehow after germinating * Lichens and nitrogen cycling – some lichens (in particular those with cyanobacteria as a photobiont) can fix nitrogen * Lichen biogeography – the study of the current distribution of extant lichens and the reasons for those distributions * Lichen resynthesis – lichens can be artificially "recreated" by combining partners in a lab * Lichens and pedogenesis – lichens contribute to the formation of soil by breaking down rock **

Biological soil crust Biological soil crusts are communities of living organisms on the soil surface in arid and semi-arid ecosystems. They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, ...

– lichens are among the common dominant biota in biocrusts, one of the world's largest environmental community types in terms of area covered * Photosynthesis in lichens

Types of lichens

Lichen lists

Lichen taxonomical classifications

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 Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

, 119

, and around 1,000

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

. * Ascolichen – a lichen whose fungal partner is a member of the

Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...

, one of the two main fungal divisions * Basidiolichen – a lichen whose fungal partner is a member of the

, the other of the two main fungal divisions; these are far fewer in occurrence than ascolichens

Classes

Lichens fall into eight fungal classes and several subclasses: #

Agaricomycetes The Agaricomycetes are a class of fungi in the division Basidiomycota. The taxon is roughly identical to that defined for the Homobasidiomycetes (alternatively called holobasidiomycetes) by Hibbett & Thorn, with the inclusion of Auriculariales a ...

## Agaricomycetidae #

Arthoniomycetes Arthoniomycetes are a class of ascomycete fungi. It includes two orders: Arthoniales and Lichenostigmatales. Most of the taxa in these orders are tropical and subtropical lichens. Systematics Phylogenetic analysis supports the monophyly of this ...

Coniocybomycetes The Coniocybaceae are the sole family of lichen-forming fungi in the Coniocybales, which itself is the only order in the class Coniocybomycetes. The family was circumscribed by Heinrich Gottlieb Ludwig Reichenbach in 1837. Both the order and the ...

Dothideomycetes Dothideomycetes is the largest and most diverse class of ascomycete fungi. It comprises 11 orders 90 families, 1300 genera and over 19,000 known species. Traditionally, most of its members were included in the loculoascomycetes, which is not par ...

## Dothideomycetidae # Eurotiomycetes ##

Chaetothyriomycetidae Chaetothyriomycetidae is a subclass of ascomycete within the class Eurotiomycetes. Many species in Chaetothyriomycetidae are lichens. Morphology Chaetothyriomycetidae produce a cleistothecium An ascocarp, or ascoma (), is the fruiting bod ...

Lecanoromycetes Lecanoromycetes is the largest class of lichenized fungi. It belongs to the subphylum Pezizomycotina in the phylum Ascomycota. The asci (spore-bearing cells) of the Lecanoromycetes most often release spores by rostrate dehiscence. Genera of unc ...

Acarosporomycetidae The Acarosporomycetidae are a subclass of fungi in the class Lecanoromycetes. This subclass contains the single order Acarosporales, which circumscribes the single family Acarosporaceae. External linksOutline of Ascomycota 2007 Acarosporal ...

Lecanoromycetidae The Lecanoromycetidae are a subclass of fungi in the class Lecanoromycetes. This subclass contains five orders: the Caliciales , the Lecanorales , the Lecideales , the Leprocaulales , the Peltigerales , the Rhizocarpales , and the Teloschistales ...

Ostropomycetidae The Ostropomycetidae are a subclass of mostly lichen-forming fungi in the class Lecanoromycetes. The subclass was circumscribed in 2004 by Catherine Reeb, François M. Lutzoni, and Claude Roux. It contains ten orders and 36 families. Arctomiace ...

Lichinomycetes Lichinales is the sole order of ascomycete fungi in the class Lichinomycetes. It contains three families: Gloeoheppiaceae (3 genera), Lichinaceae (43 genera), and Peltulaceae (1 genus). Most species are lichenized. Lichinales was proposed in 1 ...

Sordariomycetes Sordariomycetes is a class of fungi in the subdivision Pezizomycotina (Ascomycota), consisting of 28 orders, 90 families, 1344 genera. Sordariomycetes is from the Latin sordes (filth) because some species grow in animal feces, though growth habit ...

## Sordariomycetidae

Photobiont A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Cyanolichen – a lichen with a cyanobacteria photobiont * List of lichen photobionts

Lichen metabolites

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 * List of lichen products Punctelia borreri 149849

Study of lichens

Lichenology – the study of lichens *

Acharius Medal __NOTOC__ The Acharius Medal is awarded by the International Association for Lichenology (IAL) for lifetime achievement in lichenology. The organization resolved at its 1990 meeting that it would simultaneously honor professional achievement and c ...

– awarded for lifetime achievement in lichenology * Evolution of lichens – lichenization of fungi has occurred multiple times, and several pathways towards acquiring photobionts have arisen ** Fossil lichens *

Exsiccata Exsiccata (Latin, ''gen.'' -ae, ''plur.'' -ae) is a work with "published, uniform, numbered set of preserved specimens distributed with printed labels". Typically, exsiccatae refer to numbered collections of dried herbarium specimens respectivel ...

(plural ''exsiccatae'') – a published set of preserved specimens, numbered and distributed with printed labels * 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 * Spot test (lichen) – chemical tests used to aid in species identification

Threats

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

Lichens in culture

* Edible lichen – some lichens have traditionally been used as food *

Ethnolichenology Ethnolichenology is the study of the relationship between lichens and people. Lichens have and are being used for many different purposes by human cultures across the world. The most common human use of lichens is for dye, but they have also been u ...

– a branch of

ethnobotany Ethnobotany is the study of a region's plants and their practical uses through the traditional knowledge of a local culture and people. An ethnobotanist thus strives to document the local customs involving the practical uses of local flora for m ...

that studies human usage of lichens * Lichens in popular culture **

Trouble with Lichen ''Trouble with Lichen'' (published 1960) is a science fiction novel by British writer John Wyndham. Plot summary The plot concerns a young female biochemist who discovers that a chemical extracted from an unusual strain of lichen can be used ...

– novel by John Wyndham

Lichen organizations

American Bryological and Lichenological Society The American Bryological and Lichenological Society is an organization devoted to the scientific study of all aspects of the biology of bryophytes and lichen-forming fungi and is one of the nation's oldest botanical organizations. It was origina ...

(ABLS) :* '' The Bryologist'' – peer-reviewed journal published by ABLS * Australasian Lichen Society :* '' Australasian Lichenology'' – official publication of the Australasian Lichen Society *

British Lichen Society The British Lichen Society (BLS) was founded in 1958 with the objective of promoting the study and conservation of lichen. Although the society was founded in London, UK, it is also of relevance to lichens worldwide. It has been a registered ch ...

(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

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 ''Hattoria yakushimensis'' is the only species of liverwort in the genus ''Hattoria'', in the family Anastrophyllaceae. It is endemic to Japan. Its natural habitat is temperate forests. It is threatened by habitat loss. The genus name of ''Hatto ...

'' – an international, peer-reviewed journal issued by Hattori Botanical Laboratory * '' International Journal of Mycology and Lichenology''

Citations

References

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

External links

About Lichens, from the British Lichen Society

Australian Lichens, from the Australian National Herbarium and Australian National Botanic Gardens

Lichen Basics, from the North American Mycological Association
{{DEFAULTSORT:Lichen *

Lichens A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among hypha, filaments of multiple fungus, fungi species in a mutualism (biology), mutualistic relationship.Lichens A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among hypha, filaments of multiple fungus, fungi species in a mutualism (biology), mutualistic relationship.

What is a lichen?

Nature of lichens

Morphology

Ecology

Types of lichens

Lichen lists

Lichen taxonomical classifications

Classes

Orders

Families

Genera

Species

Lichens, by growth form

Lichens, by substrate

Lichens, by region

Africa

Antarctica

Asia

Australia

Europe

North America

Oceania

Pacific

South America

Photobiont