"Lichenes" from Ernst Haeckel's Artforms of Nature, 1904

Lichen-covered tree: Grey, leafy Parmotrema perlatum on upper half of trunk; yellowy-green Flavoparmelia caperata on middle and lower half and running up the extreme right side; and the fruticose Ramalina farinacea. Tresco, Isles of Scilly, UK

Lichens ( /ˈlaɪkən/,^[1] sometimes /ˈlɪtʃən/)^[2] are composite organisms consisting of a symbiotic relationship between a fungus (the mycobiont) and a photosynthetic partner (the photobiont or phycobiont), usually either a green alga (commonly Trebouxia) or cyanobacterium (commonly Nostoc).^[3] The morphology, physiology and biochemistry of lichens are very different from those of the isolated fungus and alga in culture. Lichens occur in some of the most extreme environments on Earth—arctic tundra, hot deserts, rocky coasts, and toxic slag heaps. However, they are also abundant as epiphytes on leaves and branches in rain forests and temperate woodland, on bare rock, including walls and gravestones, and on exposed soil surfaces (e.g., Collema) in otherwise mesic habitats. Lichens are widespread and may be long-lived;^[4] however, many are also vulnerable to environmental disturbance, and may be useful to scientists in assessing the effects of air pollution,^[5][6][7] ozone depletion, and metal contamination. Lichens have also been used in making dyes and perfumes, as well as in traditional medicines.

Overview[link]

The body (thallus) of most lichens is different from those of either the fungus or alga growing separately. The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations. In many species the fungus penetrates the algal cell wall, forming penetration pegs or haustoria similar to those produced by pathogenic fungi.^[3][8] Lichens are poikilohydric, capable of surviving extremely low levels of water content.^[9] However, the re-configuration of membranes following a period of dehydration requires several minutes at least.

The algal or cyanobacterial cells are photosynthetic, and as in plants they reduce atmospheric carbon dioxide into organic carbon sugars to feed both symbionts. 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 green alga as in certain tripartite lichens, they can fix atmospheric nitrogen, complementing the activities of the green alga.

Although strains of cyanobacteria found in various cyanolichens are often closely related to one another, they differ from the most closely related free-living strains.^[10] 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. Lichen propagules (diaspores) typically contain cells from both partners, although the fungal components of so-called "fringe species" rely instead on algal cells dispersed by the “core species.”^{[citation needed]}

Lichen associations may be examples of mutualism, commensalism or even parasitism, depending on the species. Cyanobacteria in laboratory settings can grow faster when they are alone rather than when they are part of a lichen.

Recently, on 26 April 2012, scientists reported that 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 (DLR).^[11][12]

History[link]

Simon Schwendener proposed the dual theory of lichens in 1867.

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 the true nature of the lichen association began to emerge.^[13] 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.^[13] Other prominent biologists, such as Heinrich Anton de Bary, Albert Bernhard Frank, and Hermann Hellriegel were not so quick to reject Schwendener's ideas and the concept soon spread into other areas of study, such as microbial, plant, animal and human pathogens.^[13] When the complex relationships between pathogenic microorganisms and their hosts were finally identified—refuting the idea of holistic organisms—Schwendener's hypothesis began to gain popularity. Further experimental proof of the dual nature of lichens was obtained when Eugen Thomas published his results in 1939 on the first successful re-synthesis experiment.^[13]

Symbionts[link]

Living as a symbiont in a lichen appears to be a very successful way for a fungus to derive essential nutrients, as about 20% of all fungal species have acquired this mode of life. The largest number of lichenized fungi occur in the Ascomycota, with about 40% of species forming such an association.^[14] Some of these lichenized fungi occur in orders with nonlichenized fungi that live as saprotrophs or plant parasites (for example, the Leotiales, Dothideales, and Pezizales). Other lichen fungi occur in only five orders in which all members are engaged in this habit (Orders Graphidales, Gyalectales, Peltigerales, Pertusariales, and Teloschistales). Lichenized and nonlichenized fungi can even be found in the same genus or species. Overall, about 98% of lichens have an ascomycetous mycobiont . Next to the Ascomycota, the largest number of lichenized fungi occur in the unassigned fungi imperfecti. Comparatively few Basidiomycetes are lichenized, but these include agarics, such as species of Lichenomphalia, clavarioid fungi, such as species of Multiclavula, and corticioid fungi, such as species of Dictyonema.

The autotrophic symbionts occurring in lichens are simple, photosynthetic organisms commonly and traditionally known as algae. These symbionts include both prokaryotic and eukaryotic organisms. Approximately 100 species of photosynthetic partners from 40 genera and five distinct classes (prokaryotic: Cyanophyceae; eukaryotic: Trebouxiophyceae, Phaeophyceae, Chlorophyceae) have been found to associate with the lichen-forming fungi.^[15] The prokaryotes belong to the Cyanobacteria, whose representatives are often called bluegreen algae. The bluegreen algae occur as symbionts in about 8% of the known lichens. The most commonly occurring genus is Nostoc.^[16] The majority of the lichens contain eukaryotic autotrophs belonging to the Chlorophyta (green algae) or to the Xanthophyta (yellow-green algae). About 90% of all known lichens have a green algae as a symbiont, and among these, Trebouxia is the most common genus, occurring in about 40% of all lichens. The second most commonly represented green algae genus is Trentepohlia. Overall, about 100 species are known to occur as autotrophs in lichens. All the algae are probably able to exist independently in nature as well as in the lichen.^[16]

A particular fungus species and algal species are not necessarily always associated together in a lichen. One fungus, for example, can form lichens with a variety of different algae. The thalli produced by a given fungal symbiont with its differing partners will be similar, and the secondary metabolites identical, indicating that the fungus has the dominant role in determining the morphology of the lichen. Further, the same algal species can occur in association with different fungal partners. Lichens are known in which there is one fungus associated with two or even three algal species. Rarely, the reverse can occur, and two or more fungal species can interact to form the same lichen.^[16]

Both the lichen and the fungus partner bear the same scientific name, and the lichens are being integrated into the classification schemes for fungi. The alga bears its own scientific name, which bears no relationship to that of the lichen or fungi.^[14]

Morphology and structure[link]

Foliose lichen Parmeliopsis ambigua on a branch of a tree

Xanthoria parietina Common orange lichen

Crustose lichens on a wall

Some lichens have the aspect of leaves (foliose lichens); others cover the substrate like a crust (crustose lichens) (illustration, right), others such as the genus Ramalina adopt shrubby forms (fruticose lichens), and there are gelatinous lichens such as the genus Collema.^[17]

Although the form of a lichen is determined by the genetic material of the fungal partner, association with a photobiont is required for the development of that form. When grown in the laboratory in the absence of its photobiont, a lichen fungus develops as an undifferentiated mass of hyphae. If combined with its photobiont under appropriate conditions, its characteristic form emerges, in the process called morphogenesis (Brodo, Sharnoff & Sharnoff, 2001). 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 first found growing in a conjoined manner.

There is evidence to suggest that the lichen symbiosis is parasitic or commensalistic, rather than mutualistic (Ahmadjian 1993). However, this now needs to be re-examined in light of Coxon's work. The photosynthetic partner can exist in nature independently of the fungal partner, but not vice versa. Furthermore, photobiont cells are routinely destroyed in the course of nutrient exchange. The association is able to continue because reproduction of the photobiont cells matches the rate at which they are destroyed. (ibid.)

Under magnification, a section through a typical foliose lichen thallus reveals four layers of interlaced fungal filaments. The uppermost layer is formed by densely agglutinated fungal hyphae building a protective outer layer called the cortex, which can reach several hundred μm in thickness.^[18] This cortex may be further topped by an epicortex 0.6-1μm thick in some Parmeliaceae, which may be with or without pores, and is secreted by cells—it is not itself cellular.^[18] 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. Beneath the upper cortex is an algal layer composed of algal cells embedded in rather densely interwoven fungal hyphae. Each cell or group of cells of the photobiont is usually individually wrapped by hyphae, and in some cases penetrated by an haustorium. Beneath this algal layer is a third layer of loosely interwoven fungal hyphae without algal cells. This layer is called the medulla. Beneath the medulla, the bottom surface resembles the upper surface and is called the lower cortex, again consisting of densely packed fungal hyphae. The lower cortex often bears rootlike fungal structures known as rhizines, which serve to attach the thallus to the substrate on which it grows. Lichens also sometimes contain structures made from fungal metabolites, for example crustose lichens sometimes have a polysaccharide layer in the cortex. 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. This seems to also be true of the photobiont species involved.

Growth form[link]

Lichens are informally classified by growth form into:

• crustose (paint-like, flat), e.g., Caloplaca flavescens
• filamentous (hair-like), e.g., Ephebe lanata
• foliose (leafy), e.g., Hypogymnia physodes
• fruticose (branched), e.g., Cladonia evansii, C. subtenuis, and Usnea australis
• leprose (powdery), e.g., Lepraria incana
• squamulose (consisting of small scale-like structures, lacking a lower cortex), e.g., Normandina pulchella
• gelatinous lichens, in which the cyanobacteria produce a polysaccharide that absorbs and retains water.

Reproduction and dispersal[link]

Thalli and apothecia on a foliose lichen

Many lichens reproduce asexually, either by vegetative reproduction or through the dispersal of diaspores containing algal and fungal cells. 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. Another form of diaspore are isidia, elongated outgrowths from the thallus that break off for mechanical dispersal. Fruticose lichens in particular can easily fragment. Because of the relative lack of differentiation in the thallus, the line between diaspore formation and vegetative reproduction is often blurred. Many lichens break up into fragments when they dry, dispersing themselves by wind action, to resume growth when moisture returns.

Many lichen fungi appear to reproduce sexually in a manner typical of fungi, producing spores that are presumably the result of sexual fusion and meiosis. Following dispersal, such fungal spores must meet with a compatible algal partner before a functional lichen can form. This may be a common form of reproduction in basidiolichens, which form fruitbodies resembling their nonlichenized relatives. Among the ascolichens, spores are produced in spore-producing bodies, the three most common spore body types are the apothecia, perithecia and the pycnidia.^[19]

For reproduction, lichen possess isidia, soredia, and undergo simple fragmentation. These structures are also composed of a fungal hyphae wrapped around cyanobacteria. (Eichorn, Evert, and Raven, 2005) While the reproductive structures are all composed of the same components (Mycobiont and Photobiont) they are each unique in other ways. Isidia are small outgrowths on the exterior of the lichen. Soredia are powdery propagules that are released from the top of the thallus.^[20] In order to establish the lichen, the soredia propagules must contain both the photobiont and the mycobiont.^[21]

Growth and longevity[link]

Lichenometry[link]

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,^[22] the technique has found many applications.

Ecology[link]

Lichens must compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing. Lichens are often the first to settle in places lacking soil, constituting the sole vegetation in some extreme environments such as those found at high mountain elevations and at high latitudes.^{[citation needed]} Some survive in the tough conditions of deserts, and others on frozen soil of the Arctic regions.^[23]

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.

Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants, thus they can grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs and monuments. Many lichens also grow as epiphytes (epi- on the surface, phyte- plant) on plants, particularly on the trunks and branches of trees. When growing on plants, lichens are not parasites; they do not consume any part of the plant nor poison it. Some ground-dwelling lichens, such as members of the subgenus Cladina (reindeer lichens), however, produce allelopathic chemicals which leach into the soil and inhibit the germination of plant seeds and growth of young plants. Stability (that is, longevity) of their substrate is a major factor of lichen habitats. Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand. In these latter cases, lichens are often an important part of soil stabilization; indeed, in some desert ecosystems, vascular (higher) plant seeds cannot become established except in places where lichen crusts stabilize the sand and help retain water.

Pine forest with lichen ground-cover

The European Space Agency has discovered that lichens can survive unprotected in space. In an experiment led by Leopoldo Sancho from the Complutense University of Madrid, two species of lichen—Rhizocarpon geographicum and Xanthoria elegans—were sealed in a capsule and launched on a Russian Soyuz rocket on 31 May 2005. Once in orbit the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation. After 15 days the lichens were brought back to earth and were found to be in full health with no discernible damage from their time in orbit.^[24][25]

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.

Lichens may be eaten by some animals, such as reindeer, living in arctic regions. The larvae of a number of Lepidoptera species feed exclusively on lichens. These include Common Footman and Marbled Beauty. However, lichens are very low in protein and high in carbohydrates, making them unsuitable for some animals. Lichens are also used by the Northern Flying Squirrel for nesting, food, and a water source during winter.

Air pollution[link]

Some lichens, like 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.^[26] 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.^[27] Consequently, many environmental studies with lichens emphasize their feasibility as effective biomonitors of atmospheric quality.^[26][28]

Not all lichens are equally sensitive to air pollutants, so different lichen species show different levels of sensitivity to specific atmospheric pollutants.^[29] 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.^[30] Upon exposure to air pollution, the photobiont may use metabolic energy for repair of cellular structures that would otherwise be used for maintenance of 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.^[26]

Evolution and paleontology[link]

The evolution of lichens and the phylum Ascomycota is complex and not well understood, but because there are fifteen different classes of Ascomycetes, scientists generally believe that different lichens have evolved independently from one another through analogous evolution. Lichenized fungi have continued to evolve, developing differently than those that do not form lichens.^{[citation needed]}

Lichenization is an ancient nutritional strategy for fungi. The extreme habitats that lichens inhabit are not ordinarily conducive to producing fossils.^[31] The oldest fossil lichens in which both symbiotic partners have been recovered date to the Early Devonian Rhynie chert, about 400 million years old.^[32] The slightly older fossil Spongiophyton has also been interpreted as a lichen on morphological^[33] and isotopic^[34] grounds, although the isotopic basis is decidedly shaky.^[35] It has been suggested—although not yet proven—that the even older fossil Nematothallus was a lichen.^[36]

It has also been claimed that Ediacaran fossils were lichens;^[37] although this claim initially met with scepticism^{[citation needed]} for all Ediacaran fossils, additional evidence has been marshalled for a lichen interpretation of Dickinsonia.^[36] Lichen-like fossils consist of coccoid cells and thin filaments, preserved in marine phosphorite of the Doushantuo Formation in southern China. These fossils are thought to be 551 to 635 million years old (belonging to the Neoproterozoic era).^[38] Discovery of these fossils suggest that fungi developed symbiotic partnerships with photoautotrophs long before the evolution of vascular plants. Winfrenatia, an early zygomycetous lichen symbiosis that may have involved controlled parasitism, is an impression found in Scotland, belonging to the early Devonian times.^[39] There are also several examples of fossilized lichens embedded in amber. The fossilized Anzia is found in pieces of amber in northern Europe and dates back approximately 40 million years.^[40] Fossilized Lobaria comes from Trinity County in northern California, USA and dates back to the early to middle Miocene.^[41]

In 1995, Gargas and colleagues proposed that there were at least five independent origins of lichenization; three in the basidiomycetes and at least two in the Ascomycetes.^[42] However, Lutzoni et al. (2000) indicate that lichenization probably evolved earlier and was followed by multiple independent losses. Some non-lichen-forming fungi may have secondarily lost the ability to form a lichen association. As a result, lichenization has been viewed as a highly successful nutritional strategy.^[43][44]

Lichens were a component of the early terrestrial ecosystems, and the estimated age of the oldest terrestrial lichen fossil is 400 Ma.^[45][46] Recent (2009) studies suggest that the ancestral ecological state of the Ascomycota was saprobism, and that independent lichenization events have occurred multiple times.^[47]

Taxonomy and classification[link]

Lichens are named based on the fungal component, which plays the primary role in determining the lichen's form. The fungus typically comprises the majority of a lichen's bulk, though in filamentous and gelatinous lichens this is not always the case. The lichen fungus is typically a member of the Ascomycota—rarely a member of the Basidiomycota, and then termed basidiolichens to differentiate them from the more common ascolichens. 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.^[48] 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 following table lists the orders and families of fungi that include lichen-forming species.

Economic uses[link]

Iwatake (Umbilicaria esculenta) gathering at Kumano in Kishū, by Hiroshige II

Food[link]

Lichens are eaten by many different cultures across the world. Although some lichens are only eaten in times of famine, others are a staple food or even a delicacy. Two obstacles are often encountered when eating lichens: lichen polysaccharides are generally indigestible to humans, and lichens usually contain mildly toxic secondary compounds that should be removed before eating. Very few lichens are poisonous, but those high in vulpinic acid or usnic acid are toxic.^[49] Most poisonous lichens are yellow.

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.

Other uses[link]

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.

There are reports dating almost 2000 years of lichens being used to extract purple and red colors.^[50] 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. The pH indicator litmus is a dye extracted from the lichen genus Rocella tinctoria by boiling

Extracts from many Usnea species were used to treat wounds in Russia in the mid-twentieth century.^{[citation needed]} Historically in Europe, Lobaria pulmonaria was collected in large quantities as "Lungwort" and, due to its lung-like appearance, was sold as a cure for lung diseases. Similarly Peltigera leucophlebia was used as a supposed cure for thrush, due to the resemblance of its cephalodia to the appearance of the disease.^[3]

The substance olivetol is found to be naturally present in certain species of lichens. This is a property it shares with the cannabis plant, which internally produces the related substance olivetolic acid (before using it to biosynthesise tetrahydrocannabinol (THC)).^[51]

Lichen is used in model railroading^[52] and other modeling hobbies as a material for making trees and shrubs.

An article published in PLoS ONE indicates that certain species of Lichen degrade prions.^[53][54]

Gallery[link]

See also[link]

Fungi portal

• Ethnolichenology
• Lichenometry
• Lichenology
• Olivetol

References[link]

Bibliography[link]

• Ahmadjian V. (1993). The Lichen Symbiosis. New York: John Wiley & Sons. ISBN 0-471-57885-1. 
• Brodo, I.M., S.D. Sharnoff, and S. Sharnoff, 2001. Lichens of North America. Yale University Press, New Haven.
• Gilbert, O. 2004. The Lichen Hunters. The Book Guild Ltd. England.
• Haugan, Reidar / Timdal, Einar (1992): Squamarina scopulorum (Lecanoraceae), a new lichen species from Norway. Nordic Journal of Botany 12(3): 357-360.
• Hawksworth, D.L. and Seaward, M.R.D. 1977. Lichenology in the British Isles 1568 - 1975. The Richmond Publishing Co. Ltd., 1977.
• Kershaw, K.A. Physiological Ecology of Lichens, 1985. Cambridge University Press Cambridge.
• Kirk PM, Cannon PF, Minter DW, Stalpers JA. (2008). Dictionary of the Fungi. (10th ed.). Wallingford: CABI. ISBN 978-0-85199-826-8. 
• Knowles M.C. (1929). "Lichens of Ireland". Proceedings of the Royal Irish Academy 38: 1–32. 
• Purvis, O.W., Coppins, B.J., Hawksworth, D.L., James, P.W. and Moore, D.M. (Editors) 1992. The Lichen Flora of Great Britain and Ireland. Natural History Museum, London.
• Sanders W.B. (2001). "Lichens: interface between mycology and plant morphology". BioScience 51 (12): 1025–1035. DOI:10.1641/0006-3568(2001)051[1025:LTIBMA]2.0.CO;2. 
• Seaward M.R.D. (1984). "Census Catalogue of Irish Lichens". Glasra 8: 1–32. 
• Whelan, P. 2011. Lichens of Ireland. The Collins Press, Cork, Ireland.

External links[link]

Wikimedia Commons has media related to: Lichens

• LIAS light: an online interactive identification key for the lichen species of the World
• University of Sydney lichen biology
• Memorial University's NL Nature project, focusing primarily on lichens
• ESA article on lichen survivability in low earth orbit
• The British Lichen Society
• Lichens of Ireland
• Lichens of North America
• Lichen Information and Pictures at blackturtle.us
• Pacific Northwest Fungi Online Journal, includes articles on lichens
• Fungi that discovered agriculture
• Pictures of Tropical Lichens
• High Resolution 1.5 Gigapixel Image of a Lichen Covered Rock
• Good example of a Lichen
• How To Grow Lichen
•  "Lichens". New International Encyclopedia. 1905. 
•  "Lichens". Encyclopedia Americana. 1920. 

Aphex Twin
In Turin, Italy in March 2007.
Background information
Birth name	Richard David James
Born	(1971-08-18) 18 August 1971 (age 40) Limerick, Ireland
Origin	Lanner, Cornwall, United Kingdom
Genres	Electronic, ambient, IDM, acid techno
Occupations	Musician, composer, remixer
Instruments	Synthesizers, piano, electronics, harpsichord, organ, percussion, laptop, softsynth, turntables, drum machine, guitar, bass guitar, computer, sequencer, sampler
Years active	1985–present
Labels	Warp Records Sire Records Rephlex Records
Associated acts	Universal Indicator, Mike & Rich

Richard David James (born 18 August 1971), best known under the pseudonym Aphex Twin, is a British electronic musician and composer. He founded the record label Rephlex Records in 1991 with Grant Wilson-Claridge. He was described by The Guardian as "the most inventive and influential figure in contemporary electronic music."^[1]

Aphex Twin has also recorded music under the aliases AFX, Blue Calx, Bradley Strider, Caustic Window, DJ Smojphace, GAK, Martin Tressider, Polygon Window, Power-Pill, Prichard D. Jams, Q-Chastic, Tahnaiya Russell, The Dice Man, Soit-P.P., and speculatively The Tuss.

Aphex Twin has released recordings on Rephlex, Warp, R&S, Sire, Mighty Force, Rabbit City, and Men Records.

History[link]

Early years[link]

Richard David James was born to Welsh parents Lorna and Derek James in St. Munchin's Limerick Regional Maternity Hospital, Ireland. He grew up in Lanner, Cornwall, enjoying, along with two older sisters, a "very happy" childhood during which they, according to James, "were pretty much left to do what [they] wanted."^[2] He "liked growing up there, being cut off from the city and the rest of the world".^[3] James attended Redruth School, located in Redruth, Cornwall.^[4]

According to musician Benjamin Middleton, James started producing music at the age of 12.^[5] As a teenager he was a disc jockey at the Shire Horse Inn in St Ives, with Tom Middleton at the Bowgie Inn in Crantock, and also along the numerous beaches around Cornwall. James studied for a National Diploma in Engineering from 1988 to 1990 (aged 16 to 18) at Cornwall College. Talking about his studies, James has said that "music and electronics went hand in hand."^[6] James graduated from college; according to an engineering lecturer, however, he often had his headphones on during practical lessons, "no doubt thinking through the mixes he'd be working on later".^[7]

Early career: early 1990s[link]

In 1989 James met and befriended Grant Wilson-Claridge when working as a DJ on alternate weeks at the Bowgie pub, near Newquay in Cornwall. Wilson-Claridge was intrigued by James's sets and was surprised to discover that James was playing tapes of his own music.

James' first release was the 12-inch EP Analogue Bubblebath on Mighty Force Records in 1991. It was first released under the moniker Aphex Twin, later changed to AFX. The track "En Trance to Exit" was made in collaboration with Tom Middleton, also known as Schizophrenia.^[8] The EP got on the playlist of Kiss FM, an influential London radio station, which helped the release to become a success.^[9]

In 1991, James and Wilson-Claridge founded Rephlex Records to promote "innovation in the dynamics of Acid — a much-loved and -misunderstood genre of house music forgotten by some and indeed new to others, especially in Britain."^[10]

Between 1991 and 1993, James released two Analogue Bubblebath EPs as AFX, and an EP under Bradley Strider, Bradley's Beat. James moved to London to take an electronics course at Kingston Polytechnic, but at the time admitted to David Toop that his "electronics studies were already slipping away as a career in the techno business took precedence." After quitting his course, James remained in London and released a number of albums and EPs on Warp Records and other labels under many aliases including AFX, Polygon Window, and Power-Pill. A number of James' tracks (released under the aliases Blue Calx, The Dice Man, and others) appeared on various compilations. Local legend has it that James lived on the roundabout in Elephant and Castle, South London during his early years in the capital - in fact he lived in a nearby disused bank.^[2][11]

Gaining success: 1992–1995[link]

	"Ageispolis" noicon Sample of "Ageispolis" from the album Selected Ambient Works 85-92.
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	"Ventolin (Video Version)" noicon Sample of "Ventolin (Video Version)" from the album ...I Care Because You Do.
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The first full-length Aphex Twin album, Selected Ambient Works 85–92, was released in 1992 on R&S Records. It received high ratings and praise from critics. John Bush of Allmusic described it as a "watershed of ambient music".^[12] In 2002, Rolling Stone wrote of the album: "Aphex Twin expanded way beyond the ambient music of Brian Eno by fusing lush soundscapes with oceanic beats and bass lines."^[13] Pitchfork Media's review called it, "among the most interesting music ever created with a keyboard and a computer."^[14] Critics also noted that the songs were recorded on cassette and that the sound quality was "relatively poor".

In 1992, he also released the EPs Xylem Tube EP and Digeridoo (first played by DJ Colin Faver on London's Kiss FM) as Aphex Twin, as Power-Pill the Pac-Man EP based on the arcade game Pac-Man, and two of his four Caustic Window EPs. "Digeridoo" reached #55 in the UK Singles Chart, and was later described as foreshadowing drum and bass by Rolling Stone.^[15] "Digeridoo" was recorded initially for the benefit of FIZZ-BOMB (at the Shire Horse, St Ives, Cornwall). These early releases came out on Rephlex Records, Mighty Force of Exeter, and R&S Records of Belgium.^[16]

In 1993, James released Analogue Bubblebath 3. He also released a single titled "On"; his second Bradley Strider EP, Bradley's Robot; two more Caustic Window EPs; and his first releases on Warp Records, Surfing on Sine Waves and "Quoth" under the alias Polygon Window.

Warp Records pressed and released a follow-up to Selected Ambient Works 85-92, Selected Ambient Works Volume II in 1994. The sound was much less beat and melody-driven than the previous volume. All of the track names were described with pie chart symbols, each of which was meant to be paired with a corresponding image in the album jacket, with exception for one song, which was named "Blue Calx". To decipher song titles, listeners had to compare the length of each track with the size of each pie chart symbol. For example, the first title, which is often labelled cliffs, is realised by pairing the first symbol with the first image, which is that of a rocky cliffside.^[17] James claimed in The Wire magazine and other media that these songs were inspired by lucid dreams and synaesthesia. Other releases are a fourth Analogue Bubblebath; GAK, derived from early demos sent to Warp Records; and Classics, a compilation album that includes "Digeridoo" and the Xylem Tube EP.

For his 1995 release, ...I Care Because You Do, James used an image of his face for the album cover, a motif that would continue on many of his later records. The album was a compilation of songs composed between 1990 and 1994 and represented a mish-mash of Aphex Twin's various music styles. This was James's last record of the 1990s to use mostly analogue synthesizers. He commissioned Western classical-music composer Philip Glass to create an orchestral version of one of the songs from this album, "Icct Hedral", which appeared on the Donkey Rhubarb EP.^[18]

Jungle, DSP, and laptops: 1995–1999[link]

In 1995 (primarily with Hangable Auto Bulb, a near anagram of Analogue Bubblebath), James began releasing more material composed on computers, combining a jungle sound with nostalgic childhood themes and computer-generated acid lines.

James's early adoption of software synthesizers predated the later popularity of using computers to make music. In the mid-to-late 1990s, his music gradually gained more mainstream appeal, as he released Richard D. James Album and Expert Knob Twiddlers (a collaboration with fellow dance producer µ-ziq) in 1996, "Come to Daddy" in 1997 (#36 on UK charts) and "Windowlicker" in 1999 (#16 on UK charts). Two pop songs that heavily use Digital Signal Processing (DSP) techniques, "Come to Daddy" and "Windowlicker" were shown on MTV and became cover features for music magazines such as NME. The videos for both singles were directed by British artist Chris Cunningham and caused controversy on release because of their disturbing images and themes.

In 1998, Aphex Twin's track "[rhubarb]" (from Selected Ambient Works Volume II) appeared as part of the BBC's digital widescreen test transmission, which was on loop for many months as the service was introduced across the UK.^[19]

Prepared piano, laptops, and more DSP: 2000–2003[link]

In 2001 Aphex Twin released drukqs, a two-CD album that featured computer controlled piano songs influenced by Erik Satie and John Cage. Many of the tracks' names are written in the Cornish language (i.e., 'jynweythek' translatable as 'machinemusic'). Also included were abrasive, fast, and meticulously programmed computer-made songs. Rolling Stone described the piano songs as "aimlessly pretty".^[20] Some reviewers concluded that drukqs was released as a contract breaker with Warp Records—a credible guess, as James's next big release was released on his own Rephlex label. James claimed to interviewers he had accidentally left an MP3 player labelled "Aphex Twin—unreleased tracks" on a plane, containing a large set of new songs, and rushed the album release to preempt an Internet leak.^[21] He also released a short EP titled 2 Remixes By AFX the same year as Drukqs. It featured two remixes, the originals being from 808 State and DJ Pierre. In addition, there is one untitled third track that consists of an SSTV image, which consists of mostly of high-pitched sounds, which can be decoded to a viewable image by proper software such as MultiMode (for Macintosh) or MMSSTV (for Windows).