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76-399: The massif varies dramatically based on slope and altitude. The eastern slopes tend to be barren, with abrupt cliffs and channels scoured into the rock by erosion from tropical storms. The western slopes tend to slope more gradually, and are partly forested. The mountains' base is tropical, but the forest gives way to thick carpets of lichen . At approximately 2,000 metres (6,600 ft), there

152-436: A holobiont . Many lichens are very sensitive to environmental disturbances and can be used to cheaply assess air pollution , ozone depletion, and metal contamination. Lichens have been used in making dyes , perfumes ( oakmoss ), and in traditional medicines . A few lichen species are eaten by insects or larger animals, such as reindeer. Lichens are widely used as environmental indicators or bio-indicators. When air

228-621: A keystone species in many ecosystems and benefit trees and birds . The English word lichen derives from the Greek λειχήν leichēn ("tree moss, lichen, lichen-like eruption on skin") via Latin lichen . The Greek noun, which literally means "licker", derives from the verb λείχειν leichein , "to lick". In American English, "lichen" is pronounced the same as the verb "liken" ( / ˈ l aɪ k ən / ). In British English, both this pronunciation and one rhyming with "kitchen" ( / ˈ l ɪ tʃ ən / ) are used. Lichens grow in

304-411: A certain shape or position to facilitate grass-cutting. Headstones of granite , marble and other kinds of stone are usually created, installed, and repaired by monumental masons . Cemeteries require regular inspection and maintenance, as stones may settle, topple and, on rare occasions, fall and injure people; or graves may simply become overgrown and their markers lost or vandalised . Restoration

380-414: A community. Some gravestones were even commissioned and erected to their own memory by people who were still living, as a testament to their wealth and status. In a Christian context , the very wealthy often erected elaborate memorials within churches rather than having simply external gravestones. Crematoria frequently offer similar alternatives to families who do not have a grave to mark, but who want

456-406: 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

532-413: 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 . 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

608-445: A discreet reference code as well to help accurately fix the location for maintenance. The cemetery owner, church, or, as in the UK , national guidelines might encourage the use of 'tasteful' and accurate wording in inscriptions. The placement of inscriptions is traditionally placed on the forward-facing side of the memorial but can also be seen in some cases on the reverse and around the edges of

684-437: A few basic internal structure types. Common names for lichens often come from a growth form or color that is typical of a lichen genus . Common groupings of lichen thallus growth forms are: 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

760-460: A focus for their mourning and for remembrance . Carved or cast commemorative plaques inside the crematorium for example may serve this purpose. A cemetery may follow national codes of practice or independently prescribe the size and use of certain materials, especially in a conservation area. Some may limit the placing of a wooden memorial to six months after burial, after which a more permanent memorial must be placed. Others may require stones of

836-407: 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 created by mucilaginous secretions. A lichen consists of a simple photosynthesizing organism, usually a green alga or cyanobacterium , surrounded by filaments of a fungus. Generally, most of a lichen's bulk

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912-402: A gravestone was the stone slab (or ledger stone ) that was laid flat over a grave . Now, all three terms ("stele", "tombstone" or "gravestone") are also used for markers set (usually upright) at the head of the grave. Some graves in the 18th century also contained footstones to demarcate the foot end of the grave. This sometimes developed into full kerb sets that marked the whole perimeter of

988-488: 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

1064-492: A headstone may settle or its fixings weaken. After several instances where unstable stones have fallen in dangerous circumstances, some burial authorities "topple test" headstones by firm pressure to check for stability. They may then tape them off or flatten them. This procedure has proved controversial in the UK, where an authority's duty of care to protect visitors is complicated because it often does not have any ownership rights over

1140-448: A host. Cyanobacteria in laboratory settings can grow faster when they are alone rather than when they are part of a lichen. 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

1216-459: 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. 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

1292-519: 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. At least one form of lichen, the North American beard-like lichens, are constituted of not two but three symbiotic partners: an ascomycetous fungus,

1368-462: 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

1444-414: A number of members of the same family. In the 19th century, headstone styles became very diverse, ranging from plain to highly decorated, and often using crosses on a base or other shapes differing from the traditional slab. By this time popular designs were shifting from symbols of death like Winged heads and Skulls to Urns and Willow trees. Marble also became overwhelmingly popular as a grave material during

1520-440: A photosynthetic alga, and, unexpectedly, a basidiomycetous yeast. Phycobionts can have a net output of sugars with only water vapor. The thallus must be saturated with liquid water for cyanobionts to photosynthesize. Algae produce sugars that are absorbed by the fungus by diffusion into special fungal hyphae called appressoria or haustoria in contact with the wall of the algal cells. The appressoria or haustoria may produce

1596-428: A protective "skin" of densely packed fungal filaments, often containing a second fungal species, which is called a cortex. Fruticose lichens have one cortex layer wrapping around the "branches". Foliose lichens have an upper cortex on the top side of the "leaf", and a separate lower cortex on the bottom side. Crustose and squamulose lichens have only an upper cortex, with the "inside" of the lichen in direct contact with

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1672-403: 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. Crustose and squamulose lichens lack a lower cortex, and the medulla is in direct contact with the substrate that the lichen grows on. In crustose areolate lichens, the edges of the areolas peel up from

1748-613: A stone. In addition, before laying a stone flat, it must be recorded for posterity. Gravestone cleaning is a practice that both professionals and volunteers can do to preserve gravestones and increase their life spans. Before cleaning any gravestones, permission must be given to the cleaner by a "descendant, the sexton , cemetery superintendent or the town, in that order. If unsure who to ask, go to your town cemetery keeper and inquire." A gravestone can be cleaned to remove human vandalism and graffiti, biological growth such as algae or lichen , and other minerals, soiling, or staining. One of

1824-476: A substance that increases permeability of the algal cell walls, and may penetrate the walls. The algae may contribute up to 80% of their sugar production to the fungus. Lichen associations may be examples of mutualism or commensalism , but the lichen relationship can be considered parasitic under circumstances where the photosynthetic partner can exist in nature independently of the fungal partner, but not vice versa. Photobiont cells are routinely destroyed in

1900-764: A surface ( substrate ) like a thick coat of paint ( crustose ); have a powder-like appearance ( leprose ); or other growth forms . 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 they are not closely related to mosses or any plant. Lichens do not have roots that absorb water and nutrients as plants do, but like plants, they produce their own nutrition by photosynthesis . When they grow on plants, they do not live as parasites , but instead use

1976-422: A wide range of shapes and forms; this external appearance is known as their morphology . The shape of a lichen is usually determined by the organization of the fungal filaments. The nonreproductive tissues, or vegetative body parts, are called the thallus . Lichens are grouped by thallus type, since the thallus is usually the most visually prominent part of the lichen. Thallus growth forms typically correspond to

2052-469: Is a belt of hardy shrubs. Above this belt the mountains are a grassland. Today, it is mainly occupied by herders and shepherds who move in a bid to find the freshest grazing grounds for their livestock. Tourists and adventurers have also visited the area as it provides both hiking and backpacking opportunities, as well as views of its geological formations. The massif is located in a relatively geologically-stable area, on solid Precambrian ground, which

2128-841: Is a hybrid colony of algae or cyanobacteria living symbiotically among filaments of multiple fungi species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualistic relationship. Lichens are the lifeform that first brought the term symbiosis (as symbiotismus ) under biological context. Lichens have since been recognized as important actors in nutrient cycling and producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails. Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but are not plants . They may have tiny, leafless branches ( fruticose ); flat leaf-like structures ( foliose ); grow crust-like, adhering tightly to

2204-663: Is a marker, usually stone , that is placed over a grave . A marker set at the head of the grave may be called a headstone . An especially old or elaborate stone slab may be called a funeral stele , stela , or slab . The use of such markers is traditional for Chinese , Jewish , Christian , and Islamic burials , as well as other traditions. In East Asia, the tomb's spirit tablet is the focus for ancestral veneration and may be removable for greater protection between rituals. Ancient grave markers typically incorporated funerary art , especially details in stone relief . With greater literacy, more markers began to include inscriptions of

2280-529: Is a specialized job for a monumental mason . Even overgrowth removal requires care to avoid damaging the carving. For example, ivy should only be cut at the base roots and left to naturally die off, never pulled off forcefully. Many materials have been used as markers. Markers sometimes bear inscriptions . The information on the headstone generally includes the name of the deceased and their date of birth and death. Such information can be useful to genealogists and local historians . Larger cemeteries may require

2356-442: 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 some macrolichens have more than one species of fungus in their tissues. Lichens are fungi that have discovered agriculture A lichen is a composite organism that emerges from algae or cyanobacteria living among

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2432-546: 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 " anastomosed ". 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

2508-526: Is evidence of the fact that these mountains were formed by a relatively sudden volcanic event. The mountains have many sharp cliffs and rises, as well as several volcanic formations. The Andringitra Massif contains many notable granite erosion sites, which have been formed over millions of years. This Madagascar location article is a stub . You can help Misplaced Pages by expanding it . Lichen A lichen ( / ˈ l aɪ k ən / LY -kən , UK also / ˈ l ɪ tʃ ən / LITCH -ən )

2584-520: Is illegible after about a hundred years... For those of you who seek a degree of immortality , a slate headstone, or as a second choice, one carved from an Irish limestone, should ensure that your name will remain on view for several centuries to come! The choice of language and/or script on gravestones has been studied by sociolinguists as indicators of language choices and language loyalty. For example, by studying cemeteries used by immigrant communities, some languages were found to be carved "long after

2660-400: Is made of interwoven fungal filaments, but this is reversed in filamentous and gelatinous lichens. The fungus is called a mycobiont . The photosynthesizing organism is called a photobiont . Algal photobionts are called phycobionts . Cyanobacteria photobionts are called cyanobionts . The part of a lichen that is not involved in reproduction, the "body" or "vegetative tissue" of a lichen,

2736-452: Is usually determined by the photosynthetic component. Special pigments, such as yellow usnic acid , give lichens a variety of colors, including reds, oranges, yellows, and browns, especially in exposed, dry habitats. In the absence of special pigments, lichens are usually bright green to olive gray when wet, gray or grayish-green to brown when dry. This is because moisture causes the surface skin ( cortex ) to become more transparent, exposing

2812-403: Is very badly polluted with sulphur dioxide, there may be no lichens present; only some green algae can tolerate those conditions. If the air is clean, then shrubby, hairy and leafy lichens become abundant. A few lichen species can tolerate fairly high levels of pollution, and are commonly found in urban areas, on pavements, walls and tree bark. The most sensitive lichens are shrubby and leafy, while

2888-453: The acrostic message "KFC tortures birds". The group placed its grave marker to promote its contention that KFC is cruel to chickens. Gravestones may be simple upright slabs with semi-circular, rounded, gabled, pointed-arched, pedimental, square or other shaped tops. During the 18th century, they were often decorated with memento mori (symbolic reminders of death ) such as skulls or winged skulls, winged cherub heads, heavenly crowns, or

2964-436: The apoplast . Secondary metabolites are thought to play a role in preference for some substrates over others. Lichens often have a regular but very slow growth rate of less than a millimeter per year. In crustose lichens, the area along the margin is where the most active growth is taking place. Most crustose lichens grow only 1–2 mm in diameter per year. Lichens may be long-lived , with some considered to be among

3040-416: 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. In three different lineages the fungal partner has independently lost the mitochondrial gene atp9, which has key functions in mitochondrial energy production. The loss makes

3116-731: The 1800s in the United States. More elaborately carved markers, such as crosses or angels also became popular during this time. Simple curb surrounds, sometimes filled with glass chippings, were popular during the mid-20th century. Islamic headstones are traditionally more a rectangular upright shaft, often topped with a carved topknot symbolic of a turban ; but in Western countries more local styles are often used. Some form of simple decoration may be employed. Special emblems on tombstones indicate several familiar themes in many faiths. Some examples are: Greek letters might also be used: Over time

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3192-602: The United States alone, pre-purchased headstones with pre-carved death years beginning with 19–. Bas-relief carvings of a religious nature or of a profile of the deceased can be seen on some headstones, especially up to the 19th century. Since the invention of photography, a gravestone might include a framed photograph or cameo of the deceased; photographic images or artwork (showing the loved one, or some other image relevant to their life, interests or achievements) are sometimes now engraved onto smooth stone surfaces. Some headstones use lettering made of white metal fixed into

3268-420: 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 a 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

3344-422: The blink of an eye. We captured the whole world through our courage and strength, Yet could take nothing with us to our grave." Or a simpler warning of inevitability of death: Remember me as you pass by, As you are now, so once was I, As I am now, so you will be, Prepare for death and follow me. Headstone engravers faced their own " year 2000 problem " when still-living people, as many as 500,000 in

3420-468: The central Brooks Range of northern Alaska have been given a maximum possible age of 10,000–11,500 years. Unlike simple dehydration in plants and animals, lichens may experience a complete loss of body water in dry periods. Lichens are capable of surviving extremely low levels of water content ( poikilohydric ). They quickly absorb water when it becomes available again, becoming soft and fleshy. Gravestones A gravestone or tombstone

3496-445: The characteristic cortex of the lichen thallus, and could also be important for its shape. 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

3572-435: The course of nutrient exchange. The association continues because reproduction of the photobiont cells matches the rate at which they are destroyed. 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 ( haustoria ) similar to those produced by pathogenic fungi that feed on

3648-428: The dangerous marker. Authorities that have knocked over stones during testing or have unilaterally lifted and laid flat any potentially hazardous stones have been criticised, after grieving relatives have discovered that their relative's marker has been moved. Since 2007 Consistory Court and local authority guidance now restricts the force used in a topple test and requires an authority to consult relatives before moving

3724-403: The deceased's name, date of birth, and date of death, often along with a personal message or prayer . The presence of a frame for photographs of the deceased is also increasingly common. The stele (plural: stelae ), as it is called in an archaeological context, is one of the oldest forms of funerary art . Originally, a tombstone was the stone lid of a stone coffin , or the coffin itself, and

3800-461: The different types of stone available: The use of slate for this plaque was a good choice as it weathers very slowly and the quality of the carved lettering remains good for many years. Many (Irish) gravestones from the mid 1700s and 1800s are made of slate. This is fortunate for those interested in tracing genealogies , as many of the inscriptions can still be read after two hundred years. This contrasts sharply with lettering cut into granite, which

3876-539: The dust enclosèd here. Blest be the man that spares these stones, And cursed be he that moves my bones. Or a warning about mortality , such as this Persian poetry carved on an ancient tombstone in the Tajiki capital of Dushanbe . I heard that mighty Jamshed the King Carved on a stone near a spring of water these words: "Many – like us – sat here by this spring And left this life in

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3952-640: The edges lift up. Gelatinous lichens may appear leafy when dry. 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. Lichens come in many colors. Coloration

4028-441: The filaments ( hyphae ) of the 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

4104-421: The fungi completely dependent on their symbionts. 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

4180-501: The fungi, algae, or cyanobacteria have the potential to engage with other microorganisms in a functioning system that may evolve as an even more complex composite organism . Lichens may be long-lived , with some considered to be among the oldest living things. They are among the first living things to grow on fresh rock exposed after an event such as a landslide. The long life-span and slow and regular growth rate of some species can be used to date events ( lichenometry ). Lichens are

4256-460: The fungus living inside the lichen; thus they are not considered to be part of the lichen. Moisture makes the cortex become more transparent. 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. Lichens can show intense antioxidant activity. Secondary metabolites are often deposited as crystals in

4332-539: The grave. Footstones were rarely annotated with more than the deceased's initials and year of death, and sometimes a memorial mason and plot reference number. Many cemeteries and churchyards have removed those extra stones to ease grass cutting by machine mower. In some UK cemeteries, the principal, and indeed only, marker is placed at the foot of the grave. Owing to soil movement and downhill creep on gentle slopes, older headstones and footstones can often be found tilted at an angle. Over time, this movement can result in

4408-472: The green photobiont layer. Different colored lichens covering large areas of exposed rock surfaces, or lichens covering or hanging from bark can be a spectacular display when the patches of diverse colors "come to life" or "glow" in brilliant displays following rain. 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

4484-441: 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

4560-543: The language ceased to be spoken" in the communities. In other cases, a language used in the inscription may indicate a religious affiliation. Marker inscriptions have also been used for political purposes, such as the grave marker installed in January 2008 at Cave Hill Cemetery in Louisville, Kentucky by Mathew Prescott, an employee of PETA . The grave marker is located near the grave of KFC founder Harland Sanders and bears

4636-409: 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

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4712-420: The most tolerant lichens are all crusty in appearance. Since industrialisation, many of the shrubby and leafy lichens such as Ramalina , Usnea and Lobaria species have very limited ranges, often being confined to the areas which have the cleanest air. 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

4788-539: The oldest living organisms. Lifespan is difficult to measure because what defines the "same" individual lichen is not precise. Lichens grow by vegetatively breaking off a piece, which may or may not be defined as the "same" lichen, and two lichens can merge, then becoming the "same" lichen. One specimen of Rhizocarpon geographicum on East Baffin Island has an estimated age of 9500 years. Thalli of Rhizocarpon geographicum and Rhizocarpon eupetraeoides / inarense in

4864-414: The photobiont "leak" out the products of photosynthesis, where they can then be absorbed by the fungus. It appears many, probably the majority, of lichen also live in a symbiotic relationship with an order of basidiomycete yeasts called Cyphobasidiales . The absence of this third partner could explain why growing lichen in the laboratory is difficult. The yeast cells are responsible for the formation of

4940-434: 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 foliose 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

5016-418: The picks and shovels of the gravedigger . Somewhat unusual were more elaborate allegorical figures , such as Old Father Time , or emblems of trade or status , or even some event from the life of the deceased (particularly how they died). Large tomb chests, false sarcophagi as the actual remains were in the earth below, or smaller coped chests were commonly used by the gentry as a means of commemorating

5092-442: The plant's surface as a substrate. Lichens occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. They are abundant growing on bark, leaves , mosses, or other lichens and hanging from branches "living on thin air" ( epiphytes ) in rainforests and in temperate woodland . They grow on rock, walls, gravestones , roofs , exposed soil surfaces, rubber, bones, and in

5168-506: The soil as part of biological soil crusts . Various lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra , hot dry deserts , rocky coasts , and toxic slag heaps. They can even live inside solid rock, growing between the grains ( endolithic ). There are about 20,000 known species. Some lichens have lost the ability to reproduce sexually, yet continue to speciate . They can be seen as being relatively self-contained miniature ecosystems , where

5244-519: The stone itself. Some families request that an inscription be made on the portion of the memorial that will be underground. In addition, some gravestones also bear epitaphs in praise of the deceased or quotations from religious texts, such as " requiescat in pace ". In a few instances the inscription is in the form of a plea, admonishment, testament of faith, claim to fame or even a curse – William Shakespeare 's inscription famously declares Good friend, for Jesus' sake forbear, To dig

5320-475: The stone, which is easy to read but can be damaged by ivy or frost. Deep carvings on a hard-wearing stone may weather many centuries exposed in graveyards and still remain legible. Those fixed on the inside of churches , on the walls , or on the floor (often as near the altar as possible) may last much longer: such memorials were often embellished with a monumental brass . Irish geologist Patrick Wyse Jackson mused on gravestone legibility in 1993 with regards to

5396-428: The stones being sited several metres away from their original location. Graves and any related memorials are a focus for mourning and remembrance. The names of relatives are often added to a gravestone over the years, so that one marker may chronicle the passing of an entire family spread over decades. Since gravestones and a plot in a cemetery or churchyard cost money, they are also a symbol of wealth or prominence in

5472-412: 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

5548-438: The substrate because it is separated from it by a tightly packed lower cortex. Gelatinous, 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

5624-410: 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. The color of a lichen changes depending on whether the lichen is wet or dry. Color descriptions used for identification are based on the color that shows when the lichen is dry. Dry lichens with a cyanobacterium as

5700-492: The surface they grow on (the substrate ). Even if the edges peel up from the substrate and appear flat and leaf-like, they lack a lower cortex, unlike foliose lichens. Filamentous, byssoid, leprose, gelatinous, and other lichens do not have a cortex; in other words, they are ecorticate . 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

5776-472: The symbiont layer is called the medulla . The medulla is less densely packed with fungal filaments than the layers above. In foliose lichens, as in Peltigera , there is usually another densely packed layer of fungal filaments called the lower cortex. Root-like fungal structures called rhizines ( usually ) grow from the lower cortex to attach or anchor the lichen to the substrate. Fruticose lichens have

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