A LICHEN is a composite organism that arises from algae or
cyanobacteria living among filaments of multiple fungi in a
symbiotic relationship . The combined lichen has properties
different from those of its component organisms.
A MACROLICHEN is a lichen that is either bush-like or leafy; all
other lichens are termed MICROLICHENS. Here, "macro" and "micro" do
not refer to size, but to the growth form. Common names for lichens
may contain the word "moss " (e.g., "reindeer moss ", "Iceland moss
"), and lichens may superficially look like and grow with mosses, but
lichens are not related to mosses or any plant. :3
It is estimated that 6% of Earth's land surface is covered by lichen. :2 There are about 20,000 known species of lichens. Some lichens have lost the ability to reproduce sexually, yet continue to speciate . Recent perspectives on lichens include that they are relatively self-contained miniature ecosystems in and of themselves, possibly with more microorganisms living with the fungi, algae, or cyanobacteria, performing other functions as partners in a system that evolves as an even more complex composite organism .
* 1 Pronunciation
* 2 Growth forms
* 2.1 Color * 2.2 Internal structure and growth forms
* 3 Physiology
* 3.2 Ecology
* 3.2.1 Miniature ecosystem and holobiont theory * 3.2.2 Lichenicolous fungi
* 3.3 Reaction to water * 3.4 Metabolites, metabolite structures and bioactivity * 3.5 Growth rate * 3.6 Life span * 3.7 Response to environmental stress
* 4 Reproduction and dispersal
* 4.1 Vegetative reproduction * 4.2 Sexual reproduction
* 5 Taxonomy and classification
* 5.1 Fungi * 5.2 Photobionts * 5.3 Controversy over classification method and species names * 5.4 Diversity * 5.5 Identification methods * 5.6 Evolution and paleontology
* 6 Ecology and interactions with environment
* 6.1 Substrates and habitats
* 7 Human use
* 8 History * 9 Gallery * 10 See also * 11 Notes * 12 References
* 13 External links
* 13.1 Identification and classification * 13.2 Internal structure * 13.3 Miscellanea * 13.4 Societies * 13.5 By region * 13.6 Images * 13.7 Cultivation * 13.8 Historic
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.
Main article: Lichen growth forms
Common groupings of lichen thallus growth forms are:
* fruticose – growing like a tuft or multiple-branched leafless mini-shrub, upright or hanging down, 3-dimensional branches with nearly round cross section (terete ) or flattened * foliose – growing in 2-dimensional, flat, leaf-like lobes * crustose – crust-like, adhering tightly to a surface (substrate ) like a thick coat of paint * squamulose - formed of small leaf-like scales crustose below but free at the tips * leprose – powdery * gelatinous – jelly like * filamentous – stringy or like matted hair * byssoid – wispy, like teased wool * structureless
There are variations in growth types in a single lichen species, grey areas between the growth type descriptions, and overlapping between growth types, so some authors might describe lichens using different growth type descriptions.
When a crustose lichen gets old, the center may start to crack up like old-dried paint, old-broken asphalt paving, or like the polygonal "islands" of cracked-up mud in a dried lakebed. This is called being rimose or areolate , and the "island" pieces separated by the cracks are called areolas . The areolas appear separated, but are (or were) connected by an underlying "prothallus" or "hypothallus". When a crustose lichen grows from a center and appears to radiate out, it is called crustose placodioid . When the edges of the areolas lift up from the substrate, it is called squamulose . :159
These growth form groups are not precisely defined. Foliose lichens may sometimes branch and appear to be fruticose. Fruticose lichens may have flattened branching parts and appear leafy. Squamulose lichens may appear where the edges lift up. Gelatinous lichens may appear leafy when dry. :159 Means of telling them apart in these cases are in the sections below.
Structures involved in reproduction often appear as discs, bumps, or squiggly lines on the surface of the thallus. :4 The thallus is not always the part of the lichen that is most visually noticeable. Some lichens can grow inside solid rock between the grains (endolithic lichens ), with only the sexual fruiting part visible growing outside the rock. These may be dramatic in color or appearance. Forms of these sexual parts are not in the above growth form categories. The most visually noticeable reproductive parts are often circular, raised, plate-like or disc-like outgrowths, with crinkly edges, and are described in sections below.
Different colored lichens may inhabit different adjacent sections of a rock face, depending on the angle of exposure to light. Colonies of lichens may be spectacular in appearance, dominating much of the surface of the visual landscape in forests and natural places, such as the vertical "paint" covering the vast rock faces of Yosemite National Park .
Color is used in identification. :4 Color changes depending on when a lichen is wet or dry. Color descriptions when used for identification are based on when the lichen is dry. Dry lichens with a cyanobacterium as the photosynthetic partner tend to be dark grey, brown, or black.
The underside of the leaf-like lobes of foliose lichens is a different color from the top side (dorsiventral ), often brown or black, sometimes white. A fruticose lichen may have flattened "branches", appearing similar to a foiliose lichen, but the underside of a leaf-like structure on a fruticose lichen is the same color as the top side. The leaf-like lobes of a foliose lichen may branch, giving the appearance of a fruticose lichen, but the underside will be a different color from the top side.
The sheen on some jelly-like gelatinous lichens is from mucilaginous secretions.
INTERNAL STRUCTURE AND GROWTH FORMS
The cyanobacterium Hyella caespitosa with fungal hyphae in the lichen Pyrenocollema halodytes
A lichen consists of a simple photosynthesizing organism, usually
green algae or cyanobacteria , surrounded by filaments of a fungus.
Generally, most of a lichen's bulk is made of interwoven fungal
filaments, although in filamentous and gelatinous lichens this is
not the case. The fungus is called a MYCOBIONT. The photosynthesizing
organism is called a PHOTOBIONT.
Algal photobionts are called
The part of a lichen that is not involved in reproduction, the "body" or "vegetative tissue" of a lichen, is called the THALLUS. The thallus form is very different from any form where the fungus or alga are growing separately. The thallus is made up of filaments of the fungus called HYPHAE . The filaments grow by branching then rejoining to create a mesh, which is called being "anastomose ". The mesh of fungal filaments may be dense or loose.
Generally, the fungal mesh surrounds the algal or cyanobacterial
cells, often enclosing them within complex fungal tissues that are
unique to lichen associations. The thallus may or may not have a
protective "skin" of densely packed fungal filaments, often containing
a second fungal species, which is called a CORTEX.
have one cortex layer wrapping around the "branches".
have an upper cortex on the top side of the "leaf", and a separate
lower cortex on the bottom side.
Fruticose, foliose, crustose, and squamulose lichens generally have up to three different types of tissue, differentiated by having different densities of fungal filaments. The top layer, where the lichen contacts the environment, is called a CORTEX. The cortex is made of densely tightly woven, packed, and glued together (agglutinated ) fungal filaments. The dense packing makes the cortex act like a protective "skin", keeping other organisms out, and reducing the intensity of sunlight on the layers below. The cortex layer can be up to several hundred micrometers (μm) in thickness (less than a millimeter). The cortex may be further topped by an epicortex of secretions, not cells, 0.6–1 μm thick in some lichens . This secretion layer may or may not have pores.
Below the cortex layer is a layer called the PHOTOBIONTIC LAYER or SYMBIONT LAYER. The symbiont layer has less densely packed fungal filaments, with the photosynthetic partner embedded in them. The less dense packing allows air circulation during photosynthesis, similar to the anatomy of a leaf. Each cell or group of cells of the photobiont is usually individually wrapped by hyphae, and in some cases penetrated by an haustorium . In crustose and foliose lichens, algae in the photobiontic layer are diffuse among the fungal filaments, decreasing in gradation into the layer below. In fruticose lichens, the photobiontic layer is sharply distinct from the layer below.
The layer beneath the symbiont layer called is called the MEDULLA .
The medulla is less densely packed with fungal filaments than the
layers above. In foliose lichens, there is usually, as in
:159 another densely packed layer of fungal filaments called the lower
cortex. Root-like fungal structures called RHIZINES (usually ) :159
grow from the lower cortex to attach or anchor the lichen to the
Fruticose lichens have a single cortex wrapping all the
way around the "stems" and "branches". The medulla is the lowest
layer, and may form a cottony white inner core for the branchlike
thallus, or it may be hollow. :159
In crustose areolate lichens, the edges of the areolas peel up from the substrate and appear leafy. In squamulose lichens the part of the lichen thallus that is not attached to the substrate may also appear leafy. But these leafy parts lack a lower cortex, which distinguishes crustose and squamulose lichens from foliose lichens. Conversely, foliose lichens may appear flattened against the substrate like a crustose lichen, but most of the leaf-like lobes can be lifted up from the substrate because it is separated from it by a tightly packed lower cortex.
Gelatinous, :159 byssoid, and leprose lichens lack a cortex (are ecorticate ), and generally have only undifferentiated tissue, similar to only having a symbiont layer.
In lichens that include both green algal and cyanobacterial symbionts, the cyanobacteria may be held on the upper or lower surface in small pustules called CEPHALODIA .
PRUINIA is a whitish coating on top of an upper surface. An EPINECRAL LAYER is "a layer of horny dead fungal hyphae with indistinct lumina in or near the cortex above the algal layer".
In August 2016, it was reported that macrolichens have more than one species of fungus in their tissues.
A lichen is a composite organism that emerges from algae or cyanobacteria living among the filaments (hyphae ) of two fungi in a mutually beneficial symbiotic relationship. The fungi benefit from the carbohydrates produced by the algae or cyanobacteria via photosynthesis . The algae or cyanobacteria benefit by being protected from the environment by the filaments of the fungi, which also gather moisture and nutrients from the environment, and (usually) provide an anchor to it. Although some photosynthetic partners in a lichen can survive outside the lichen, the lichen symbiotic association extends the ecological range of both partners, whereby most descriptions of lichen associations describe them as symbiotic. However, while symbiotic, the relationship is probably not mutualistic , since the algae give up a disproportionate amount of their sugars (see below). Both partners gain water and mineral nutrients mainly from the atmosphere, through rain and dust. The fungal partner protects the alga by retaining water, serving as a larger capture area for mineral nutrients and, in some cases, provides minerals obtained from the substrate . If a cyanobacterium is present, as a primary partner or another symbiont in addition to a green alga as in certain tripartite lichens, they can fix atmospheric nitrogen , complementing the activities of the green alga.
The algal or cyanobacterial cells are photosynthetic and, as in plants, they reduce atmospheric carbon dioxide into organic carbon sugars to feed both symbionts. Phycobionts (algae) produce sugar alcohols (ribitol , sorbitol , and erythritol ), which are absorbed by the mycobiont (fungus). Cyanobionts produce glucose . Lichenized fungal cells can make the photobiont "leak" out the products of photosynthesis, where they can then be absorbed by the fungus. :5
The lichen combination of alga or cyanobacterium with a fungus has a very different form (morphology), physiology, and biochemistry than the component fungus, alga, or cyanobacterium growing by itself, naturally or in culture. The body (thallus ) of most lichens is different from those of either the fungus or alga growing separately. When grown in the laboratory in the absence of its photobiont, a lichen fungus develops as a structureless, undifferentiated mass of fungal filaments (hyphae ). If combined with its photobiont under appropriate conditions, its characteristic form associated with the photobiont emerges, in the process called morphogenesis . In a few remarkable cases, a single lichen fungus can develop into two very different lichen forms when associating with either a green algal or a cyanobacterial symbiont. Quite naturally, these alternative forms were at first considered to be different species, until they were found growing in a conjoined manner.
Evidence that lichens are examples of successful symbiosis is the fact that lichens can be found in almost every habitat and geographic area on the planet. Two species in two genera of green algae are found in over 35% of all lichens, but can only rarely be found living on their own outside of a lichen.
In a case where one fungal partner simultaneously had two green algae partners that outperform each other in different climates, this might indicate having more than one photosynthetic partner at the same time might enable the lichen to exist in a wider range of habitats and geographic locations.
Phycobionts can have a net output of sugars with only water vapor. The thallus must be saturated with liquid water for cyanobionts to photosynthesize.
Miniature Ecosystem And Holobiont Theory
Symbiosis in lichens is so well-balanced that lichens have been considered to be relatively self-contained miniature ecosystems in and of themselves. It is thought that lichens may be even more complex symbiotic systems that include non-photosynthetic bacterial communities performing other functions as partners in a holobiont .
Many lichens are very sensitive to environmental disturbances and can
be used in cheaply assessing air pollution , ozone depletion, and
Some fungi can only be found living on lichens as obligate parasites . These are referred to as lichenicolous fungi , and are a different species from the fungus living inside the lichen; thus they are not considered to be part of the lichen.
REACTION TO WATER
Moisture makes the cortex become more transparent. :4 This way, the algae can conduct photosynthesis when moisture is available, and is protected at other times. When the cortex is more transparent, the algae show more clearly and the lichen looks greener.
METABOLITES, METABOLITE STRUCTURES AND BIOACTIVITY
Sometimes lichens contain structures made from fungal metabolites , for example crustose lichens sometimes have a polysaccharide layer in the cortex.
In crustose lichens, the area along the margin is where the most active growth is taking place. :159 Most crustose lichens grow only 1–2 mm in diameter per year.
RESPONSE TO ENVIRONMENTAL STRESS
Unlike simple dehydration in plants and animals, lichens may
experience a complete loss of body water in dry periods.
In tests, lichen survived and showed remarkable results on the
adaptation capacity of photosynthetic activity within the simulation
time of 34 days under Martian conditions in the Mars Simulation
Laboratory (MSL) maintained by the
German Aerospace Center
European Space Agency
REPRODUCTION AND DISPERSAL
Xanthoparmelia sp. with dark-colored reproductive structures (disc-like apothecia ) at center, surrounded by a pale coloured vegetative thallus .
Many lichens reproduce asexually, either by a piece breaking off and
growing on its own (vegetative reproduction ) or through the dispersal
of diaspores containing a few algal cells surrounded by fungal cells.
Because of the relative lack of differentiation in the thallus, the
line between diaspore formation and vegetative reproduction is often
Fruticose lichens can easily fragment, and new lichens can
grow from the fragment (vegetative reproduction ). Many lichens break
up into fragments when they dry, dispersing themselves by wind action,
to resume growth when moisture returns. SOREDIA (singular:
"soredium") are small groups of algal cells surrounded by fungal
filaments that form in structures called soralia, from which the
soredia can be dispersed by wind. ISIDIA (singular: "isidium") are
branched, spiny, elongated, outgrowths from the thallus that break off
for mechanical dispersal.
Disc-like apothecia (left) and thallus (right) on a foliose lichen
Structures involved in reproduction often appear as discs, bumps, or squiggly lines on the surface of the thallus. :4 Only the fungal partner in a lichen reproduces sexually. Many lichen fungi reproduce sexually like other fungi, producing spores formed by meiosis and fusion of gametes. Following dispersal, such fungal spores must meet with a compatible algal partner before a functional lichen can form.
Some lichen fungi belong to Basidiomycetes (BASIDIOLICHENS) and produce mushroom -like reproductive structures resembling those of their nonlichenized relatives.
Most lichen fungi belong to
The three most common spore body types are raised discs called
APOTHECIA (singular: apothecium), bottle-like cups with a small hole
at the top called PERITHECIA (singular: perithecium), and PYCNIDIA
(singular: pycnidium), shaped like perithecia but without asci (an
ascus is the structure that contains and releases the sexual spores in
fungi of the
The apothecium has a layer of exposed spore-producing cells called ASCI (singular: ascus), and is usually a different color from the thallus tissue. :14 When the apothecium has an outer margin, the margin is called the EXCIPLE. :14 When the exciple has a color similar to colored thallus tissue the apothecium or lichen is called LECANORINE, meaning similar to members of the genus Lecanora . :14 When the exciple is blackened like carbon it is called LECIDEINE meaning similar to members of the genus Lecidea . :14 When the margin is pale or colorless it is called BIATORINE. :14 Crust-like thallus with pseudopodetia
A "podetium" (plural: podetia ) is a lichenized stalk-like structure of the fruiting body rising from the thallus, associated with some fungi that produce a fungal apothecium . Since it is part of the reproductive tissue, podetia are not considered part of the main body (thallus), but may be visually prominent. The podetium may be branched, and sometimes cup-like. They usually bear the fungal pycnidia or apothecia or both. Many lichens have apothecia that are visible to the naked eye.
Most lichens produce abundant sexual structures. Many species appear to disperse only by sexual spores. For example, the crustose lichens Graphis scripta and Ochrolechia parella produce no symbiotic vegetative propagules. Instead, the lichen-forming fungi of these species reproduce sexually by self-fertilization (i.e. they are homothallic ). This breeding system may enable successful reproduction in harsh environments.
MAZAEDIA (singular: mazaedium) are apothecia shaped like a dressmaker\'s pin in (pin lichen )s, where the fruiting body is a brown or black mass of loose ascospores enclosed by a cup-shaped exciple, which sits on top of a tiny stalk. :15
TAXONOMY AND CLASSIFICATION
"LICHENIZED FUNGUS" may refer to the entire lichen, or to just the fungus. This may cause confusion without context. A particular fungus species may form lichens with different algae species, giving rise to what appear to be different lichen species, but which are still classified (as of 2014) as the same lichen species.
Formerly, some lichen taxonomists placed lichens in their own division, the MYCOPHYCOPHYTA, but this practice is no longer accepted because the components belong to separate lineages . Neither the ascolichens nor the basidiolichens form monophyletic lineages in their respective fungal phyla, but they do form several major solely or primarily lichen-forming groups within each phylum. Even more unusual than basidiolichens is the fungus Geosiphon pyriforme , a member of the Glomeromycota that is unique in that it encloses a cyanobacterial symbiont inside its cells. Geosiphon is not usually considered to be a lichen, and its peculiar symbiosis was not recognized for many years. The genus is more closely allied to endomycorrhizal genera.
The fungal component of a lichen is called the MYCOBIONT. The mycobiont may be an Ascomycete or Basidiomycete . The associated lichens are called either ascolichens or basidiolichens , respectively. Living as a symbiont in a lichen appears to be a successful way for a fungus to derive essential nutrients since about 20% of all fungal species have acquired this mode of life.
Thalli produced by a given fungal symbiont with its differing
partners may be similar, and the secondary metabolites identical,
indicating that the fungus has the dominant role in determining the
morphology of the lichen. But the same mycobiont with different
photobionts may also produce very different growth forms.
Although each lichen thallus generally appears homogeneous, some evidence seems to suggest that the fungal component may consist of more than one genetic individual of that species.
Two or more fungal species can interact to form the same lichen.
The following table lists the orders and families of fungi that include lichen-forming species.
* v * t * e
Taxonomy of the
Show all lichen genera
* Dacampiaceae * Xanthopyreniaceae
* Epigloeaceae * Arthopyreniaceae * Didymosphaeriaceae * Lichenotheliaceae * Microthyriaceae * Mycosphaerellaceae * Naetrocymbaceae * Parmulariaceae * Pseudoperisporiaceae * Pyrenotrichaceae * Protothelenellaceae
* Anziaceae * Arthrorhaphidaceae * Biatorellaceae * Caliciaceae * Candelariaceae * Cetradoniaceae * Cladoniaceae * Crocyniaceae * Dactylosporaceae * Gypsoplacaceae * Haematommataceae * Lecanoraceae * Lecideaceae * Loxosporaceae * Megalariaceae * Megalosporaceae * Mycoblastaceae * Ophioparmaceae * Parmeliaceae * Physciaceae * Pilocarpaceae * Porpidiaceae * Psoraceae * Ramalinaceae * Rhizocarpaceae * Stereocaulaceae * Sphaerophoraceae
* Arctomiaceae * Hymeneliaceae
* Atheliaceae * Lepidostromataceae
* Syzygosporaceae * Tremellaceae
* Anderson, Heidi L.; Ekman, Stefan (2005). "Disintegration of the Micareaceae (lichenized Ascomycota): a molecular phylogeny based on mitochondrial rDNA sequences". Mycological Research. 109 (1): 21–30. doi :10.1017/S0953756204001625 . * CABI Bioscience Databases. Available online at http://www.indexfungorum.org/. * Ertz, Damien; Lawrey, James D.; Sikaroodi, Masoumeh; Gillevet, Patrick M.; Fischer, Eberhard; Killmann, Dorothee; Sérusiaux, Emmanuël (2008). "A new lineage of lichenized basidiomycetes inferred from a two-gene phylogeny: The Lepidostromataceae with three species from the tropics". American Journal of Botany. 95 (12): 1548–1556. doi :10.3732/ajb.0800232 . PMID 21628162 . * Ekman, Stefan; Andersen, Heidi L.; Wedin, Mats (2008). "The limitations of ancestral state reconstruction and the evolution of the ascus in the Lecanorales (lichenized Ascomycota)". Systematic Biology. 57 (1): 141–156. doi :10.1080/10635150801910451 . PMID 18300027 .
* Ekman, Stefan (2001). "Molecular phylogeny of the Bacidiaceae (Lecanorales, lichenized Ascomycota)". Mycological Research. 105 (7): 783–797. doi :10.1017/S0953756201004269 . * Grube, Martin; Winka, Katarina (2002). "Progress in understanding the evolution and classification of lichenized ascomycetes". Mycologist. 16 (2): 67–76. doi :10.1017/S0269-915X(02)00206-9 . * Liu, Yajuan J.; Hall, Benjamin D. (2004). "Body plan evolution of ascomycetes, as inferred from an RNA polymerase II phylogeny" . PNAS . 101 (13): 4507–4512. doi :10.1073/pnas.0400938101 . PMC 384777 . PMID 15070748 . * Schmitt, I.; Yamamoto, Y.; Lumbsch, H. T. (2006). "Phylogeny of Pertusariales (Ascomycotina): Resurrection of Ochrolechiaceae and new circumscription of Megasporaceae". Journal of the Hattori Botanical Laboratory. 100: 753–764. * Staiger, Bettina; Kalb, Klaus; Grube, Martin (2006). "Phylogeny and phenotypic variation in the lichen family Graphidaceae (Ostropomycetidae, Ascomycota)". Mycological Research. 110 (7): 765–772. doi :10.1016/j.mycres.2006.05.003 . PMID 16876697 .
The photosynthetic partner in a lichen is called a PHOTOBIONT. The
photobionts in lichens come from a variety of simple prokaryotic and
eukaryotic organisms. In the majority of lichens the photobiont is a
green alga (
Common algal photobionts are from the genus Trebouxia , Trentepohlia , Pseudotrebouxia , or Myrmecia (algae) . Trebouxia is the most common genus of green algae in lichens, occurring in about 40% of all lichens. "Trebouxioid" means either a photobiont that is in the genus Trebouxia , or resembles a member of that genus, and is therefore presumably a member of the class Trebouxiophyceae . The second most commonly represented green alga genus is Trentepohlia . Overall, about 100 species of eukaryotes are known to occur as photobionts in lichens. All the algae are probably able to exist independently in nature as well as in the lichen.
A "cyanolichen " is a lichen with a cyanobacterium as its main photosynthetic component (photobiont). The most commonly occurring cyanobacterium genus is Nostoc . Other common cyanobacterium photobionts are from Scytonema . Many cyanolichens are small and black, and have limestone as the substrate. Another cyanolichen group, the jelly lichens of the genera Collema or Leptogium are gelatinous and live on moist soils. Another group of large and foliose species including Peltigera , Lobaria , and Degelia are grey-blue, especially when dampened or wet. Many of these characterize the Lobarion communities of higher rainfall areas in western Britain, e.g., in the Celtic rain forest . Strains of cyanobacteria found in various cyanolichens are often closely related to one another. They differ from the most closely related free-living strains.
The lichen association is a close symbiosis. It extends the
ecological range of both partners but is not always obligatory for
their growth and reproduction in natural environments, since many of
the algal symbionts can live independently. A prominent example is the
alga Trentepohlia , which forms orange-coloured populations on tree
trunks and suitable rock faces.
The same cyanobiont species can occur in association with different fungal species as lichen partners. The same phycobiont species can occur in association with different fungal species as lichen partners. More than one phycobiont may be present in a single thallus.
Although each lichen thallus generally appears homogeneous, some evidence seems to suggest that the photobiont component may consist of more than one genetic individual of that species. A single lichen may contain several algal genotypes . These multiple genotypes may better enable response to adaptation to environmental changes, and enable the lichen to inhabit a wider range of environments.
CONTROVERSY OVER CLASSIFICATION METHOD AND SPECIES NAMES
There are about 20,000 known lichen species . But what is meant by
"species" is different from what is meant by biological species in
plants, animals, or fungi, where being the same species implies that
there is a common ancestral lineage . Because lichens are
combinations of members of two or even three different biological
kingdoms , these components must have a different ancestral lineage
from each other. By convention, lichens are still called "species"
anyway, and are classified according to the species of their fungus,
not the species of the algae or cyanobacteria.
Depending on context, "lichenized fungus" may refer to the entire
lichen, or to the fungus when it is in the lichen, which can be grown
in culture in isolation from the algae or cyanobacteria. Some algae
and cyanobacteria are found naturally living outside of the lichen.
The fungal, algal, or cyanobacterial component of a lichen can be
grown by itself in culture. When growing by themselves, the fungus,
algae, or cyanobacteria have very different properties than those of
The same fungus growing in combination with different algae or cyanobacteria, can produce lichens that are very different in most properties, meeting non-DNA criteria for being different "species". Historically, these different combinations were classified as different species. When the fungus is identified as being the same using modern DNA methods, these apparently different species get reclassified as the same species under the current (2014) convention for classification by fungal component. This has led to debate about this classification convention. These apparently different "species" have their own independent evolutionary history.
There is also debate as to the appropriateness of giving the same binomial name to the fungus, and to the lichen that combines that fungus with an alga or cyanobacterium (synecdoche ). This is especially the case when combining the same fungus with different algae or cyanobacteria produces dramatically different lichen organisms, which would be considered different species by any measure other than the DNA of the fungal component. If the whole lichen produced by the same fungus growing in association with different algae or cyanobacteria, were to be classified as different "species", the number of "lichen species" would be greater.
The largest number of lichenized fungi occur in the
"Pd " refers to the outcome of the Pd test or is used as an abbreviation for the chemical used in the test, para-phenylenediamine . If putting a drop on a lichen turns an area bright yellow to orange, this helps identify it as belonging to either the genus Cladonia or Lecanora .
EVOLUTION AND PALEONTOLOGY
The fossil record for lichens is poor. The extreme habitats that
lichens dominate, such as tundra, mountains, and deserts, are not
ordinarily conducive to producing fossils. There are fossilized
lichens embedded in amber. The fossilized Anzia is found in pieces of
amber in northern Europe and dates back approximately 40 million
The oldest fossil lichens in which both symbiotic partners have been
recovered date to the Early
The ancestral ecological state of both
Glomeromycota may extend well back into the Precambrian.
Winfrenatia, an early zygomycetous (
Glomeromycota ) lichen symbiosis
that may have involved controlled parasitism, is permineralized in the
ECOLOGY AND INTERACTIONS WITH ENVIRONMENT
SUBSTRATES AND HABITATS
When growing on mineral surfaces, some lichens slowly decompose their substrate by chemically degrading and physically disrupting the minerals, contributing to the process of weathering by which rocks are gradually turned into soil. While this contribution to weathering is usually benign, it can cause problems for artificial stone structures. For example, there is an ongoing lichen growth problem on Mount Rushmore National Memorial that requires the employment of mountain-climbing conservators to clean the monument.
In the arctic tundra, lichens, together with mosses and liverworts , make up the majority of the ground cover , which helps insulate the ground and may provide forage for grazing animals. An example is " Reindeer moss ", which is a lichen, not a moss.
A crustose lichen that grows on rock is called a SAXICOLOUS LICHEN .
LICHENS AND SOILS
In addition to distinct physical mechanisms by which lichens break down raw stone, recent studies indicate lichens attack stone chemically, entering newly chelated minerals into the ecology.
The lichen exudates, which have powerful chelating capacity, the widespread occurrence of mineral neoformation, particularly metal oxalates, together with the characteristics of weathered substrates, all confirm the significance of lichens as chemical weathering agents.
Over time, this activity creates new fertile soil from lifeless stone.
A major ecophysiological advantage of lichens is that they are
poikilohydric (poikilo- variable, hydric- relating to water), meaning
that though they have little control over the status of their
hydration, they can tolerate irregular and extended periods of severe
desiccation . Like some mosses , liverworts , ferns , and a few
"resurrection plants ", upon desiccation, lichens enter a metabolic
suspension or stasis (known as cryptobiosis ) in which the cells of
the lichen symbionts are dehydrated to a degree that halts most
biochemical activity. In this cryptobiotic state, lichens can survive
wider extremes of temperature, radiation and drought in the harsh
environments they often inhabit.
EFFECTS OF AIR POLLUTION
Some lichens, like the foliose Lobaria pulmonaria , are sensitive to air pollution.
If lichens are exposed to air pollutants at all times, without any deciduous parts, they are unable to avoid the accumulation of pollutants. Also lacking stomata and a cuticle , lichens may absorb aerosols and gases over the entire thallus surface from which they may readily diffuse to the photobiont layer. Because lichens do not possess roots, their primary source of most elements is the air, and therefore elemental levels in lichens often reflect the accumulated composition of ambient air. The processes by which atmospheric deposition occurs include fog and dew , gaseous absorption, and dry deposition. Consequently, many environmental studies with lichens emphasize their feasibility as effective biomonitors of atmospheric quality.
Not all lichens are equally sensitive to air pollutants , so different lichen species show different levels of sensitivity to specific atmospheric pollutants. The sensitivity of a lichen to air pollution is directly related to the energy needs of the mycobiont, so that the stronger the dependency of the mycobiont on the photobiont, the more sensitive the lichen is to air pollution. Upon exposure to air pollution, the photobiont may use metabolic energy for repair of its cellular structures that would otherwise be used for maintenance of its photosynthetic activity, therefore leaving less metabolic energy available for the mycobiont. The alteration of the balance between the photobiont and mycobiont can lead to the breakdown of the symbiotic association. Therefore, lichen decline may result not only from the accumulation of toxic substances, but also from altered nutrient supplies that favor one symbiont over the other.
This interaction between lichens and air pollution has been used as a means of monitoring air quality since 1859, with more systematic methods developed by William Nylander in 1866.
Further information: Ethnolichenology
In the past Iceland moss (Cetraria islandica) was an important human food in northern Europe, and was cooked as a bread, porridge, pudding, soup, or salad. Wila (Bryoria fremontii) was an important food in parts of North America, where it was usually pitcooked. Northern peoples in North America and Siberia traditionally eat the partially digested reindeer lichen (Cladina spp.) after they remove it from the rumen of caribou or reindeer that have been killed. Rock tripe (Umbilicaria spp. and Lasalia spp.) is a lichen that has frequently been used as an emergency food in North America, and one species, Umbilicaria esculenta , is used in a variety of traditional Korean and Japanese foods.
Main article: Lichenometry
Lichenometry is a technique used to determine the age of exposed rock
surfaces based on the size of lichen thalli. Introduced by Beschel in
the 1950s, the technique has found many applications. it is used in
archaeology , palaeontology , and geomorphology . It uses the presumed
regular but slow rate of lichen growth to determine the age of exposed
rock . :9 Measuring the diameter (or other size measurement) of the
largest lichen of a species on a rock surface indicates the length of
time since the rock surface was first exposed.
Many lichens produce secondary compounds, including pigments that reduce harmful amounts of sunlight and powerful toxins that reduce herbivory or kill bacteria. These compounds are very useful for lichen identification, and have had economic importance as dyes such as cudbear or primitive antibiotics .
The pH indicator (indicated acidic or basic) in the litmus test is a dye extracted from the lichen Roccella tinctoria by boiling.
In the Highlands of Scotland, traditional dyes for
There are reports dating almost 2000 years old of lichens being used to make purple and red dyes. Of great historical and commercial significance are lichens belonging to the family Roccellaceae , commonly called orchella weed or orchil. Orcein and other lichen dyes have largely been replaced by synthetic versions.
TRADITIONAL MEDICINE AND RESEARCH
Historically in traditional medicine of Europe, Lobaria pulmonaria was collected in large quantities as "Lungwort", due to its lung-like appearance (the doctrine of signatures suggesting that herbs can treat body parts that they physically resemble). Similarly, Peltigera leucophlebia was used as a supposed cure for thrush , due to the resemblance of its cephalodia to the appearance of the disease.
Pine forest with Cladonia lichen ground-cover
Colonies of lichens may be spectacular in appearance, dominating the
surface of the visual landscape as part of the aesthetic appeal to
paying visitors of
Yosemite National Park
In early Midrashic literature, the Hebrew word "vayilafeth" in Ruth 3:8 is explained as referring to Ruth entwining herself around Boaz like lichen. The tenth century Arab physician, Al-Tamimi , mentions lichens dissolved in vinegar and rose water being used in his day for the treatment of skin diseases and rashes.
"Lichenes" fancifully drawn by
Although lichens had been recognized as organisms for quite some time, it was not until 1867, when Swiss botanist Simon Schwendener proposed his dual theory of lichens, that lichens are a combination of fungi with algae or cyanobacteria, whereby the true nature of the lichen association began to emerge. Schwendener's hypothesis, which at the time lacked experimental evidence, arose from his extensive analysis of the anatomy and development in lichens, algae, and fungi using a light microscope . Many of the leading lichenologists at the time, such as James Crombie and Nylander , rejected Schwendener's hypothesis because the common consensus was that all living organisms were autonomous.
Other prominent biologists, such as
Heinrich Anton de Bary , Albert
Bernhard Frank ,
Melchior Treub and
In the 2010s, a new facet of the fungi-algae partnership was discovered. Toby Spribille and colleagues found that many types of lichen that were long thought to be ascomycete -algae pairs were actually ascomycete-basidiomycete -algae trios.
Lobaria pulmonaria , tree lungwort, lung lichen, lung moss; Upper Bavaria, Germany *
Cladonia macilenta var. bacillaris 'Lipstick Cladonia' *
Hypogymnia cf. tubulosa with Bryoria sp. and Tuckermannopsis sp. in the Canadian Rockies *
Letharia sp. with Bryoria sp. on pine branches near Blackpine Lake, Washington State *
Lobaria oregana , commonly called 'Lettuce lichen', in the Hoh Rainforest , Washington State
Xanthoparmelia cf. lavicola, a foliose lichen, on basalt. *
Map lichen ( Rhizocarpon geographicum ) on rock *
Physcia millegrana (a foliose lichen), with an unlichenized polypore fungus (bottom right), on a fallen log. *
Cladonia cf. cristatella, a lichen commonly referred to as 'British Soldiers'. Notice the red tips. *
A crusty crustose lichen on a wall *
Foliose lichens on rock growing outward and dying in the center. These lichens are at least several decades old. *
Microscopic view of lichen growing on a piece of concrete dust.
* ^ This was scraped from a dry, concrete-paved section of a drainage ditch. This entire image covers a square that is approximately 1.7 millimeters on a side. The numbered ticks on the scale represent distances of 230 micrometers, or slightly less than 0.25 millimeter.
* ^ A B C D Spribille, Toby; Tuovinen, Veera; Resl, Philipp;
Vanderpool, Dan; Wolinski, Heimo; Aime, M. Catherine; Schneider,
Kevin; Stabentheiner, Edith; Toome-Heller, Merje (2016-07-21).
Basidiomycete yeasts in the cortex of ascomycete macrolichens".
Science. 353: 488–92.
Bibcode :2016Sci...353..488S. doi
:10.1126/science.aaf8287 . ISSN 0036-8075 . PMID 27445309 .
* ^ A B C D E F G H I J K L M N O P "What is a lichen?". Australian
National Botanic Gardens. Retrieved 10 October 2014.
* ^ Introduction to
* ^ Taylor WA, Free CB, Helgemo R, Ochoada J (2004). "SEM analysis
of spongiophyton interpreted as a fossil lichen". International
Journal of Plant Sciences. 165 (5): 875–881. doi :10.1086/422129 .
* ^ Jahren, A.H.; Porter, S.; Kuglitsch, J.J. (2003). "Lichen
metabolism identified in Early
* ^ Treub, Melchior (1873) Onderzoekingen over de natuur der lichenen. Dissertation Leiden University. * ^ Yong, Ed (2016-07-21), "How a guy from a Montana trailer park overturned 150 years of biology", The Atlantic, retrieved 2017-07-23.
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Look up LICHEN in Wiktionary, the free dictionary.
IDENTIFICATION AND CLASSIFICATION
* LIAS light: an online interactive