Euripides was a tragedian of classical Athens. Along with Aeschylus and Sophocles, he is one of the three ancient Greek tragedians for whom a significant number of plays have survived; some ancient scholars attributed 95 plays to him but, according to the Suda, it was 92 at most. Of these, 18 or 19 have survived more or less complete and there are fragments, some substantial, of most of the other plays. More of his plays have survived intact than those of Aeschylus and Sophocles together because his popularity grew as theirs declined—he became, in the Hellenistic Age, a cornerstone of ancient literary education, along with Homer and Menander. Euripides is identified with theatrical innovations that have profoundly influenced drama down to modern times in the representation of traditional, mythical heroes as ordinary people in extraordinary circumstances; this new approach led him to pioneer developments that writers adapted to comedy, some of which are characteristic of romance. Yet he became "the most tragic of poets", focusing on the inner lives and motives of his characters in a way unknown.
He was "the creator of...that cage, the theatre of Shakespeare's Othello, Racine's Phèdre, of Ibsen and Strindberg," in which "...imprisoned men and women destroy each other by the intensity of their loves and hates", yet he was the literary ancestor of comic dramatists as diverse as Menander and George Bernard Shaw. Unique among writers of Ancient Athens, Euripides demonstrated sympathy towards the underrepresented members of society, his male contemporaries were shocked by the'heresies' he put into the mouths of characters, such as these words of his heroine Medea: His contemporaries associated him with Socrates as a leader of a decadent intellectualism, both of them being lampooned by comic poets such as Aristophanes. Whereas Socrates was put on trial and executed as a corrupting influence, Euripides chose a voluntary exile in old age, dying in Macedonia. Recent scholarship casts doubt on ancient biographies of Euripides. For example, it is possible that he never visited Macedonia at all, or, if he did, he might have been drawn there by King Archelaus with incentives that were offered to other artists.
Traditional accounts of the author's life are found in many commentaries and include details such as these: He was born on Salamis Island around 480 BC, with parents Cleito and Mnesarchus, a retailer who lived in a village near Athens. Upon the receipt of an oracle saying that his son was fated to win "crowns of victory", Mnesarchus insisted that the boy should train for a career in athletics. In fact the boy was destined for a career on the stage, where however he was to win only five victories, one of, after his death, he served for a short time as both torch-bearer at the rites of Apollo Zosterius. His education was not confined to athletics: he studied painting and philosophy under the masters Prodicus and Anaxagoras, he had two disastrous marriages and both his wives—Melite and Choerine —were unfaithful. He became a recluse. "There he built an impressive library and pursued daily communion with the sea and sky". He retired to the "rustic court" of King Archelaus in Macedonia, where he died in 406 BC.
However, as mentioned in the introduction, biographical details such as these should be regarded with scepticism. They are derived entirely from three unreliable sources: folklore, employed by the ancients to lend colour to the lives of celebrated authors; this biography is divided into three sections corresponding to the three kinds of sources. Euripides was the youngest in a set of three great tragedians who were contemporaries: his first play was staged thirteen years after Sophocles' debut and only three years after Aeschylus's masterpiece, the Oresteia; the identity of the threesome is neatly underscored by a patriotic account of their roles during Greece's great victory over Persia at the Battle of Salamis—Aeschylus fought there, Sophocles was just old enough to celebrate the victory in a boys' chorus and Euripides was born on the day of the battle. The apocryphal account that he composed his works in a cave on Salamis island was a late tradition and it symbolizes the isolation of an intellectual, rather ahead of his time.
Much of his life and his whole career coincided with the struggle between Athens and Sparta for hegemony in Greece but he didn't live to see the final defeat of his city. It is said that he died in Macedonia after being attacked by the Molossian hounds of King Archelaus and that his cenotaph near Piraeus was struck by lightning—signs of his unique powers, whether for good or ill. In an account by Plutarch, the catastrophic failure of the Sicilian expedition led Athenians to trade renditions of Euripides' lyrics to their enemies in return for food and drink. Plutarch is the source for the story that the victorious Spartan generals, having planned the demolition of Athens and the enslavement of its people, grew merciful after being entertained at a banquet by lyrics from Euripides' play Electra: "they felt that it would be a barbarous act to annihilate a ci
A mushroom, or toadstool, is the fleshy, spore-bearing fruiting body of a fungus produced above ground on soil or on its food source. The standard for the name "mushroom" is Agaricus bisporus. "Mushroom" describes a variety of other gilled fungi, with or without stems, therefore the term is used to describe the fleshy fruiting bodies of some Ascomycota. These gills produce microscopic spores that help the fungus spread across the ground or its occupant surface. Forms deviating from the standard morphology have more specific names, such as "bolete", "puffball", "stinkhorn", "morel", gilled mushrooms themselves are called "agarics" in reference to their similarity to Agaricus or their order Agaricales. By extension, the term "mushroom" can refer to either the entire fungus when in culture, the thallus of species forming the fruiting bodies called mushrooms, or the species itself. Identifying mushrooms requires a basic understanding of their macroscopic structure. Most are gilled, their spores, called basidiospores, are produced on the gills and fall in a fine rain of powder from under the caps as a result.
At the microscopic level, the basidiospores are shot off basidia and fall between the gills in the dead air space. As a result, for most mushrooms, if the cap is cut off and placed gill-side-down overnight, a powdery impression reflecting the shape of the gills is formed; the color of the powdery print, called a spore print, is used to help classify mushrooms and can help to identify them. Spore print colors include white, black, purple-brown, pink and creamy, but never blue, green, or red. While modern identification of mushrooms is becoming molecular, the standard methods for identification are still used by most and have developed into a fine art harking back to medieval times and the Victorian era, combined with microscopic examination; the presence of juices upon breaking, bruising reactions, tastes, shades of color, habitat and season are all considered by both amateur and professional mycologists. Tasting and smelling mushrooms carries its own hazards because of poisons and allergens.
Chemical tests are used for some genera. In general, identification to genus can be accomplished in the field using a local mushroom guide. Identification to species, requires more effort. However, over-mature specimens cease producing spores. Many novices have mistaken humid water marks on paper for white spore prints, or discolored paper from oozing liquids on lamella edges for colored spored prints. Typical mushrooms are the fruit bodies of members of the order Agaricales, whose type genus is Agaricus and type species is the field mushroom, Agaricus campestris. However, in modern molecularly defined classifications, not all members of the order Agaricales produce mushroom fruit bodies, many other gilled fungi, collectively called mushrooms, occur in other orders of the class Agaricomycetes. For example, chanterelles are in the Cantharellales, false chanterelles such as Gomphus are in the Gomphales, milk-cap mushrooms and russulas, as well as Lentinellus, are in the Russulales, while the tough, leathery genera Lentinus and Panus are among the Polyporales, but Neolentinus is in the Gloeophyllales, the little pin-mushroom genus, along with similar genera, are in the Hymenochaetales.
Within the main body of mushrooms, in the Agaricales, are common fungi like the common fairy-ring mushroom, enoki, oyster mushrooms, fly agarics and other Amanitas, magic mushrooms like species of Psilocybe, paddy straw mushrooms, shaggy manes, etc. An atypical mushroom is the lobster mushroom, a deformed, cooked-lobster-colored parasitized fruitbody of a Russula or Lactarius and deformed by the mycoparasitic Ascomycete Hypomyces lactifluorum. Other mushrooms are not gilled, so the term "mushroom" is loosely used, giving a full account of their classifications is difficult; some have pores underneath, others have spines, such as the hedgehog mushroom and other tooth fungi, so on. "Mushroom" has been used for polypores, jelly fungi, coral fungi, bracket fungi and cup fungi. Thus, the term is more one of common application to macroscopic fungal fruiting bodies than one having precise taxonomic meaning. 14,000 species of mushrooms are described. The terms "mushroom" and "toadstool" go back centuries and were never defined, nor was there consensus on application.
Between 1400 and 1600 AD, the terms mushrom, muscheron, mussheron, or musserouns were used. The term "mushroom" and its variations may have been derived from the French word mousseron in reference to moss. Delineation between edible and poisonous fungi is not clear-cut, so a "mushroom" may be edible, poisonous, or unpalatable. Cultural or social phobias of mushrooms and fungi may be related; the term "fungophobia" was coined by William Delisle Hay of England, who noted a national superstition or fear of "toadstools". The word "toadstool" has apparent analogies in German Krötenschwamm. In German folklore and old fair
The Middle East is a transcontinental region centered on Western Asia and Egypt. Saudi Arabia is geographically the largest Middle Eastern nation; the corresponding adjective is Middle Eastern and the derived noun is Middle Easterner. The term has come into wider usage as a replacement of the term Near East beginning in the early 20th century. Arabs, Persians and Azeris constitute the largest ethnic groups in the region by population. Arabs constitute the largest ethnic group in the region by a clear margin. Indigenous minorities of the Middle East include Jews, Assyrians, Copts, Lurs, Samaritans, Shabaks and Zazas. European ethnic groups that form a diaspora in the region include Albanians, Circassians, Crimean Tatars, Franco-Levantines, Italo-Levantines. Among other migrant populations are Chinese, Indians, Pakistanis, Pashtuns and sub-Saharan Africans; the history of the Middle East dates back to ancient times, with the importance of the region being recognized for millennia. Several major religions have their origins in the Middle East, including Judaism and Islam.
The Middle East has a hot, arid climate, with several major rivers providing irrigation to support agriculture in limited areas such as the Nile Delta in Egypt, the Tigris and Euphrates watersheds of Mesopotamia, most of what is known as the Fertile Crescent. Most of the countries that border the Persian Gulf have vast reserves of crude oil, with monarchs of the Arabian Peninsula in particular benefiting economically from petroleum exports; the term "Middle East" may have originated in the 1850s in the British India Office. However, it became more known when American naval strategist Alfred Thayer Mahan used the term in 1902 to "designate the area between Arabia and India". During this time the British and Russian Empires were vying for influence in Central Asia, a rivalry which would become known as The Great Game. Mahan realized not only the strategic importance of the region, but of its center, the Persian Gulf, he labeled the area surrounding the Persian Gulf as the Middle East, said that after Egypt's Suez Canal, it was the most important passage for Britain to control in order to keep the Russians from advancing towards British India.
Mahan first used the term in his article "The Persian Gulf and International Relations", published in September 1902 in the National Review, a British journal. The Middle East, if I may adopt a term which I have not seen, will some day need its Malta, as well as its Gibraltar. Naval force has the quality of mobility; the British Navy should have the facility to concentrate in force if occasion arise, about Aden and the Persian Gulf. Mahan's article was reprinted in The Times and followed in October by a 20-article series entitled "The Middle Eastern Question," written by Sir Ignatius Valentine Chirol. During this series, Sir Ignatius expanded the definition of Middle East to include "those regions of Asia which extend to the borders of India or command the approaches to India." After the series ended in 1903, The Times removed quotation marks from subsequent uses of the term. Until World War II, it was customary to refer to areas centered around Turkey and the eastern shore of the Mediterranean as the "Near East", while the "Far East" centered on China, the Middle East meant the area from Mesopotamia to Burma, namely the area between the Near East and the Far East.
In the late 1930s, the British established the Middle East Command, based in Cairo, for its military forces in the region. After that time, the term "Middle East" gained broader usage in Europe and the United States, with the Middle East Institute founded in Washington, D. C. in 1946, among other usage. The description Middle has led to some confusion over changing definitions. Before the First World War, "Near East" was used in English to refer to the Balkans and the Ottoman Empire, while "Middle East" referred to Iran, the Caucasus, Central Asia, Turkestan. In contrast, "Far East" referred to the countries of East Asia With the disappearance of the Ottoman Empire in 1918, "Near East" fell out of common use in English, while "Middle East" came to be applied to the re-emerging countries of the Islamic world. However, the usage "Near East" was retained by a variety of academic disciplines, including archaeology and ancient history, where it describes an area identical to the term Middle East, not used by these disciplines.
The first official use of the term "Middle East" by the United States government was in the 1957 Eisenhower Doctrine, which pertained to the Suez Crisis. Secretary of State John Foster Dulles defined the Middle East as "the area lying between and including Libya on the west and Pakistan on the east and Iraq on the North and the Arabian peninsula to the south, plus the Sudan and Ethiopia." In 1958, the State Department explained that the terms "Near East" and "Middle East" were interchangeable, defined the region as including only Egypt, Israel, Jordan, Saudi Arabia, Kuwait and Qatar. The Associated Press Styleboo
China the People's Republic of China, is a country in East Asia and the world's most populous country, with a population of around 1.404 billion. Covering 9,600,000 square kilometers, it is the third- or fourth-largest country by total area. Governed by the Communist Party of China, the state exercises jurisdiction over 22 provinces, five autonomous regions, four direct-controlled municipalities, the special administrative regions of Hong Kong and Macau. China emerged as one of the world's earliest civilizations, in the fertile basin of the Yellow River in the North China Plain. For millennia, China's political system was based on hereditary monarchies, or dynasties, beginning with the semi-legendary Xia dynasty in 21st century BCE. Since China has expanded, re-unified numerous times. In the 3rd century BCE, the Qin established the first Chinese empire; the succeeding Han dynasty, which ruled from 206 BC until 220 AD, saw some of the most advanced technology at that time, including papermaking and the compass, along with agricultural and medical improvements.
The invention of gunpowder and movable type in the Tang dynasty and Northern Song completed the Four Great Inventions. Tang culture spread in Asia, as the new Silk Route brought traders to as far as Mesopotamia and Horn of Africa. Dynastic rule ended in 1912 with the Xinhai Revolution; the Chinese Civil War resulted in a division of territory in 1949, when the Communist Party of China established the People's Republic of China, a unitary one-party sovereign state on Mainland China, while the Kuomintang-led government retreated to the island of Taiwan. The political status of Taiwan remains disputed. Since the introduction of economic reforms in 1978, China's economy has been one of the world's fastest-growing with annual growth rates above 6 percent. According to the World Bank, China's GDP grew from $150 billion in 1978 to $12.24 trillion by 2017. Since 2010, China has been the world's second-largest economy by nominal GDP and since 2014, the largest economy in the world by purchasing power parity.
China is the world's largest exporter and second-largest importer of goods. China is a recognized nuclear weapons state and has the world's largest standing army and second-largest defense budget; the PRC is a permanent member of the United Nations Security Council as it replaced the ROC in 1971, as well as an active global partner of ASEAN Plus mechanism. China is a leading member of numerous formal and informal multilateral organizations, including the Shanghai Cooperation Organization, WTO, APEC, BRICS, the BCIM, the G20. In recent times, scholars have argued that it will soon be a world superpower, rivaling the United States; the word "China" has been used in English since the 16th century. It is not a word used by the Chinese themselves, it has been traced through Portuguese and Persian back to the Sanskrit word Cīna, used in ancient India."China" appears in Richard Eden's 1555 translation of the 1516 journal of the Portuguese explorer Duarte Barbosa. Barbosa's usage was derived from Persian Chīn, in turn derived from Sanskrit Cīna.
Cīna was first used including the Mahābhārata and the Laws of Manu. In 1655, Martino Martini suggested that the word China is derived from the name of the Qin dynasty. Although this derivation is still given in various sources, it is complicated by the fact that the Sanskrit word appears in pre-Qin literature; the word may have referred to a state such as Yelang. The meaning transferred to China as a whole; the origin of the Sanskrit word is still a matter of debate, according to the Oxford English Dictionary. The official name of the modern state is the "People's Republic of China"; the shorter form is "China" Zhōngguó, from zhōng and guó, a term which developed under the Western Zhou dynasty in reference to its royal demesne. It was applied to the area around Luoyi during the Eastern Zhou and to China's Central Plain before being used as an occasional synonym for the state under the Qing, it was used as a cultural concept to distinguish the Huaxia people from perceived "barbarians". The name Zhongguo is translated as "Middle Kingdom" in English.
Archaeological evidence suggests that early hominids inhabited China between 2.24 million and 250,000 years ago. The hominid fossils of Peking Man, a Homo erectus who used fire, were discovered in a cave at Zhoukoudian near Beijing; the fossilized teeth of Homo sapiens have been discovered in Fuyan Cave in Hunan. Chinese proto-writing existed in Jiahu around 7000 BCE, Damaidi around 6000 BCE, Dadiwan from 5800–5400 BCE, Banpo dating from the 5th millennium BCE; some scholars have suggested. According to Chinese tradition, the first dynasty was the Xia, which emerged around 2100 BCE; the dynasty was considered mythical by historians until scientific excavations found early Bronze Age sites at Erlitou, Henan in 1959. It remains unclear whether these sites are the remains of the Xia dynasty or of another culture from the same period; the succeeding Shang dynasty is the earliest to be confirmed by contemporary records. The Shang ruled the plain of the Yellow River in eastern China from the 17th to the 11th century BCE.
Their oracle bone script
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation. Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population, it is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules. The scientific theory of evolution by natural selection was proposed by Charles Darwin and Alfred Russel Wallace in the mid-19th century and was set out in detail in Darwin's book On the Origin of Species. Evolution by natural selection was first demonstrated by the observation that more offspring are produced than can survive.
This is followed by three observable facts about living organisms: 1) traits vary among individuals with respect to their morphology and behaviour, 2) different traits confer different rates of survival and reproduction and 3) traits can be passed from generation to generation. Thus, in successive generations members of a population are more to be replaced by the progenies of parents with favourable characteristics that have enabled them to survive and reproduce in their respective environments. In the early 20th century, other competing ideas of evolution such as mutationism and orthogenesis were refuted as the modern synthesis reconciled Darwinian evolution with classical genetics, which established adaptive evolution as being caused by natural selection acting on Mendelian genetic variation. All life on Earth shares a last universal common ancestor that lived 3.5–3.8 billion years ago. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, to fossilised multicellular organisms.
Existing patterns of biodiversity have been shaped by repeated formations of new species, changes within species and loss of species throughout the evolutionary history of life on Earth. Morphological and biochemical traits are more similar among species that share a more recent common ancestor, can be used to reconstruct phylogenetic trees. Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from the field or laboratory and on data generated by the methods of mathematical and theoretical biology, their discoveries have influenced not just the development of biology but numerous other scientific and industrial fields, including agriculture and computer science. The proposal that one type of organism could descend from another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander and Empedocles; such proposals survived into Roman times. The poet and philosopher Lucretius followed Empedocles in his masterwork De rerum natura.
In contrast to these materialistic views, Aristotelianism considered all natural things as actualisations of fixed natural possibilities, known as forms. This was part of a medieval teleological understanding of nature in which all things have an intended role to play in a divine cosmic order. Variations of this idea became the standard understanding of the Middle Ages and were integrated into Christian learning, but Aristotle did not demand that real types of organisms always correspond one-for-one with exact metaphysical forms and gave examples of how new types of living things could come to be. In the 17th century, the new method of modern science rejected the Aristotelian approach, it sought explanations of natural phenomena in terms of physical laws that were the same for all visible things and that did not require the existence of any fixed natural categories or divine cosmic order. However, this new approach was slow to take root in the biological sciences, the last bastion of the concept of fixed natural types.
John Ray applied one of the more general terms for fixed natural types, "species," to plant and animal types, but he identified each type of living thing as a species and proposed that each species could be defined by the features that perpetuated themselves generation after generation. The biological classification introduced by Carl Linnaeus in 1735 explicitly recognised the hierarchical nature of species relationships, but still viewed species as fixed according to a divine plan. Other naturalists of this time speculated on the evolutionary change of species over time according to natural laws. In 1751, Pierre Louis Maupertuis wrote of natural modifications occurring during reproduction and accumulating over many generations to produce new species. Georges-Louis Leclerc, Comte de Buffon suggested that species could degenerate into different organisms, Erasmus Darwin proposed that all warm-blooded animals could have descended from a single microorganism; the first full-fledged evolutionary scheme was Jean-Baptiste Lamarck's "transmutation" theory of 1809, which envisaged spontaneous generation continually producing simple forms of life that developed greater complexity in parallel lineages with an inherent progressive tendency, postulated that on a local level, these lineages adapted to the environment by inheriting changes caused by their use or disuse in parents.
These ideas were cond
Russia the Russian Federation, is a transcontinental country in Eastern Europe and North Asia. At 17,125,200 square kilometres, Russia is by far or by a considerable margin the largest country in the world by area, covering more than one-eighth of the Earth's inhabited land area, the ninth most populous, with about 146.77 million people as of 2019, including Crimea. About 77 % of the population live in the European part of the country. Russia's capital, Moscow, is one of the largest cities in the world and the second largest city in Europe. Extending across the entirety of Northern Asia and much of Eastern Europe, Russia spans eleven time zones and incorporates a wide range of environments and landforms. From northwest to southeast, Russia shares land borders with Norway, Estonia, Latvia and Poland, Ukraine, Azerbaijan, China and North Korea, it shares maritime borders with Japan by the Sea of Okhotsk and the U. S. state of Alaska across the Bering Strait. However, Russia recognises two more countries that border it, Abkhazia and South Ossetia, both of which are internationally recognized as parts of Georgia.
The East Slavs emerged as a recognizable group in Europe between the 3rd and 8th centuries AD. Founded and ruled by a Varangian warrior elite and their descendants, the medieval state of Rus arose in the 9th century. In 988 it adopted Orthodox Christianity from the Byzantine Empire, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Rus' disintegrated into a number of smaller states; the Grand Duchy of Moscow reunified the surrounding Russian principalities and achieved independence from the Golden Horde. By the 18th century, the nation had expanded through conquest and exploration to become the Russian Empire, the third largest empire in history, stretching from Poland on the west to Alaska on the east. Following the Russian Revolution, the Russian Soviet Federative Socialist Republic became the largest and leading constituent of the Union of Soviet Socialist Republics, the world's first constitutionally socialist state; the Soviet Union played a decisive role in the Allied victory in World War II, emerged as a recognized superpower and rival to the United States during the Cold War.
The Soviet era saw some of the most significant technological achievements of the 20th century, including the world's first human-made satellite and the launching of the first humans in space. By the end of 1990, the Soviet Union had the world's second largest economy, largest standing military in the world and the largest stockpile of weapons of mass destruction. Following the dissolution of the Soviet Union in 1991, twelve independent republics emerged from the USSR: Russia, Belarus, Uzbekistan, Azerbaijan, Kyrgyzstan, Tajikistan and the Baltic states regained independence: Estonia, Lithuania, it is governed as a federal semi-presidential republic. Russia's economy ranks as the twelfth largest by nominal GDP and sixth largest by purchasing power parity in 2018. Russia's extensive mineral and energy resources are the largest such reserves in the world, making it one of the leading producers of oil and natural gas globally; the country is one of the five recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction.
Russia is a great power as well as a regional power and has been characterised as a potential superpower. It is a permanent member of the United Nations Security Council and an active global partner of ASEAN, as well as a member of the Shanghai Cooperation Organisation, the G20, the Council of Europe, the Asia-Pacific Economic Cooperation, the Organization for Security and Co-operation in Europe, the World Trade Organization, as well as being the leading member of the Commonwealth of Independent States, the Collective Security Treaty Organization and one of the five members of the Eurasian Economic Union, along with Armenia, Belarus and Kyrgyzstan; the name Russia is derived from Rus', a medieval state populated by the East Slavs. However, this proper name became more prominent in the history, the country was called by its inhabitants "Русская Земля", which can be translated as "Russian Land" or "Land of Rus'". In order to distinguish this state from other states derived from it, it is denoted as Kievan Rus' by modern historiography.
The name Rus itself comes from the early medieval Rus' people, Swedish merchants and warriors who relocated from across the Baltic Sea and founded a state centered on Novgorod that became Kievan Rus. An old Latin version of the name Rus' was Ruthenia applied to the western and southern regions of Rus' that were adjacent to Catholic Europe; the current name of the country, Россия, comes from the Byzantine Greek designation of the Rus', Ρωσσία Rossía—spelled Ρωσία in Modern Greek. The standard way to refer to citizens of Russia is rossiyane in Russian. There are two Russian words which are commonly
A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. The combined lichen has properties different from those of its component organisms. Lichens come in many colors and forms; the properties are sometimes plant-like, but lichens are not plants. Lichens may have tiny, leafless branches, flat leaf-like structures, flakes that lie on the surface like peeling paint, a powder-like appearance, or other growth forms. A macrolichen is a lichen, either bush-like or leafy. Here, "macro" and "micro" do not refer to size, but to the growth form. Common names for lichens may contain the word moss, lichens may superficially look like and grow with mosses, but lichens are not 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 the plants as a substrate.
Lichens occur from sea level to high alpine elevations, in many environmental conditions, can grow on any surface. Lichens are abundant growing on bark, mosses, on other lichens, hanging from branches "living on thin air" in rain forests and in temperate woodland, they grow on rock, gravestones, exposed soil surfaces, in the soil as part of a biological soil crust. Different kinds of lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, toxic slag heaps, they can live inside solid rock, growing between the grains. It is estimated that 6% of Earth's land surface is covered by lichens. There are about 20,000 known species of lichens; some lichens have lost the ability to reproduce sexually, yet continue to speciate. Lichens can be seen as being self-contained miniature ecosystems, where the fungi, algae, or cyanobacteria have the potential to engage with other microorganisms in a functioning system that may evolve as an 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 lichens can be used to date events. In American English, "lichen" is pronounced the same as the verb "liken". In British English, both this pronunciation and one rhyming with "kitchen" ) are used. English lichen derives from Greek λειχήν leichēn via Latin lichen; the Greek noun, which means "licker", derives from the verb λείχειν leichein, "to lick". Lichens grow in a wide range of shapes and forms; the shape of a lichen is 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 the most visually prominent part of the lichen. Thallus growth forms correspond to a few basic internal structure types. Common names for lichens come from a growth form or color, typical of a lichen genus.
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 or flattened foliose – growing in 2-dimensional, leaf-like lobes crustose – crust-like, adhering to a surface 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 structurelessThere are variations in growth types in a single lichen species, grey areas between the growth type descriptions, 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, the "island" pieces separated by the cracks are called areolas.
The areolas appear separated, but are 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. These growth form groups are not 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. Means of telling them apart in these cases are in the sections below. Structures involved in reproduction appear as discs, bumps, or squiggly lines on the surface of the thallus; the thallus is not always the part of the lichen, most visually noticeable. Some lichens can grow inside solid rock between the grains, 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 circular, plate-like or disc-like outgrowths, with crinkly edges, are described in sections below. Lichens come in many colors. Coloratio