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''Taxus'' is a genus of
coniferous Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extant ...
trees or
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
s known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish
bark Bark may refer to: * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Places * Bark, Germany * Bark, Warmian-Masurian Voivodeship, Poland Arts, ...
, lanceolate, flat, dark-green
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
long and broad, arranged spirally on the stem, but with the leaf bases twisted to align the leaves in two flat rows either side of the stem. The oldest known fossil species are from the Early Cretaceous.


Morphology

The seed cones are highly modified, each cone containing a single seed long partly surrounded by a modified scale which develops into a soft, bright red
berry A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit, although many pips or seeds may be present. Common examples are strawberries, raspb ...
-like structure called an
aril An aril (pronounced ), also called an arillus, is a specialized outgrowth from a seed that partly or completely covers the seed. An arillode or false aril is sometimes distinguished: whereas an aril grows from the attachment point of the see ...
, long and wide and open at the end. The arils are mature 6–9 months after pollination, and with the seed contained are eaten by thrushes,
waxwing The waxwings are three species of passerine birds classified in the genus ''Bombycilla''. They are pinkish-brown and pale grey with distinctive smooth plumage in which many body feathers are not individually visible, a black and white eyestripe, ...
s and other birds, which disperse the hard seeds undamaged in their droppings; maturation of the arils is spread over 2–3 months, increasing the chances of successful seed dispersal. The male cones are globose, across, and shed their
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
in early spring. Yews are mostly
dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...
, but occasional individuals can be variably
monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is conne ...
, or change sex with time.


Taxonomy

All of the yews are very closely related to each other, and some botanists treat them all as subspecies or varieties of just one widespread species; under this treatment, the species name used is '' Taxus baccata'', the first yew described scientifically. Other sources, however, recognize 9 species, for example th
Plant List
''Taxus'' species appear similar. Attempts at taxonomy vary from describing all yews as subspecies of ''T. baccata'', as did RKF Pilger in 1903, to splitting species by even very small morphological differences, as did R. W. Spjut in 2007 with 25 species and over 50 varieties. Some species have traditionally been recognized by geographic distribution, but Asian species have been more difficult to classify. ''T. contorta'' in the Western Himalaya and ''T. sumatrana'' in Malesia are now generally agreed upon, but overlapping ranges in the
Eastern Himalaya ] The Eastern Himalayas extend from eastern Nepal across Northeast India, Bhutan, the Tibet Autonomous Region to Yunnan in China and northern Myanmar. The climate of this region is influenced by the monsoon of South Asia from June to September. It ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, and subtropical southeast Asia have led to greater confusion, with the species ''T. chinensis'', ''T. mairei'', and ''T. wallichiana'' being elucidated only in the 21st century with the aid of molecular phylogenetics. The most distinct is the Sumatran yew (''T. sumatrana'', native to
Sumatra Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...
and Celebes north to southernmost
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
), distinguished by its sparse, sickle-shaped yellow-green leaves. The Mexican yew (''T. globosa'', native to eastern Mexico south to
Honduras Honduras, officially the Republic of Honduras, is a country in Central America. The republic of Honduras is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Oce ...
) is also relatively distinct with foliage intermediate between Sumatran yew and the other species. The Florida yew, Mexican yew and Pacific yew are all rare species listed as threatened or endangered.


Toxicity

All species of yew contain highly
poison Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...
ous
taxine Taxine alkaloids, which are often named under the collective title of taxines, are the toxic chemicals that can be isolated from the yew tree. The amount of taxine alkaloids depends on the species of yew, with ''Taxus baccata'' and '' Taxus cusp ...
alkaloids, with some variation in the exact formula of the alkaloid between the species. All parts of the tree except the
aril An aril (pronounced ), also called an arillus, is a specialized outgrowth from a seed that partly or completely covers the seed. An arillode or false aril is sometimes distinguished: whereas an aril grows from the attachment point of the see ...
s contain the alkaloid. The arils are edible and sweet, but the seed is dangerously
poison Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...
ous; unlike birds, the human stomach can break down the seed coat and release the toxins into the body. This can have fatal results if yew 'berries' are eaten without removing the seeds first. Grazing animals, particularly cattle and horses, are also sometimes found dead near yew trees after eating the leaves, though deer are able to break down the poisons and will eat yew foliage freely. In the wild, deer browsing of yews is often so extensive that wild yew trees are commonly restricted to cliffs and other steep slopes inaccessible to deer. The foliage is also eaten by the larvae of some
Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...
n insects including the moth willow beauty.


Distribution

Yews occur around the globe in temperate zones of the northern hemisphere, northernmost in Norway and southernmost in the
South Celebes South Sulawesi ( id, Sulawesi Selatan) is a province in the southern peninsula of Sulawesi. The Selayar Islands archipelago to the south of Sulawesi is also part of the province. The capital is Makassar. The province is bordered by Central Sulawe ...
. Some populations exist in tropical highlands. Yews typically occur in the understory or canopy of moist temperate or tropical mountain forests. Elevation varies by latitude from in tropical forests to near sea level in its northernmost populations. Yews are common in landscape architecture, giving rise to widespread
naturalized Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country. It may be done automatically by a statute, i.e., without any effort on the part of the in ...
populations in the United States. There, both ''T. baccata'' and ''T. cuspidata'' are common ornamental shrubs. ''T. baccata'' appears throughout Europe and into western Asia. ''T. cuspidata'' occurs over much of East Asia, in China, Japan, Korea, and Sakhalin. ''T. brevifolia'' ranges in the United States from California to Montana and Alaska, while ''T. canadensis'' appears in the northeastern United States and southeast Canada.


Allergenic potential

All parts of a yew plant are toxic to humans with the exception of the yew berries (which however contain a toxic seed); additionally, male and dioecious yews in this genus release
cytotoxic Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa''). Cell physiology Treating cells ...
pollen, which can cause headaches, lethargy, aching joints, itching, and skin rashes; it is also a trigger for asthma. These pollen granules are extremely small, and can easily pass through window screens. Male yews bloom and release abundant amounts of pollen in the spring; completely female yews only trap pollen while producing none. Yews in this genus are primarily separate-sexed, and males are extremely allergenic, with an
OPALS Optical Payload for Lasercomm Science (OPALS) is a spacecraft communication instrument developed at the Jet Propulsion Laboratory that was tested on the International Space Station (ISS) from 18 April 2014 to 17 July 2014 to demonstrate the te ...
allergy scale rating of 10 out of 10. Completely female yews have an OPALS rating of 1, and are considered "allergy-fighting".


Uses and traditions


Bows

Yew wood is reddish brown (with whiter sapwood), and is very springy. It was traditionally used to make bows, especially the longbow. Latin taxus "yew tree," is probably borrowed, via Greek, from ''Taxša'', the Scythian word for yew (and bow) (cognate of Persian تخش ''Taxš'', meaning bow). British yews tend to be too gnarly, and thus the wood for English longbows used at the
Battle of Agincourt The Battle of Agincourt ( ; french: Azincourt ) was an English victory in the Hundred Years' War. It took place on 25 October 1415 (Saint Crispin's Day) near Azincourt, in northern France. The unexpected English victory against the numerica ...
was imported from Spain or northern Italy. Ötzi, the Chalcolithic mummy found in 1991 in the Italian Alps, carried an unfinished bow made of yew wood. Consequently, it is not surprising that in
Norse mythology Norse, Nordic, or Scandinavian mythology is the body of myths belonging to the North Germanic peoples, stemming from Old Norse religion and continuing after the Christianization of Scandinavia, and into the Nordic folklore of the modern period ...
, the abode of the god of the bow, Ullr, had the name Ydalir (Yew Dales). Most longbow wood used in northern Europe was imported from Iberia, where climatic conditions are better for growing the knot-free yew wood required. The yew longbow was the critical weapon used by the English in the defeat of the French
cavalry Historically, cavalry (from the French word ''cavalerie'', itself derived from "cheval" meaning "horse") are soldiers or warriors who fight mounted on horseback. Cavalry were the most mobile of the combat arms, operating as light cavalry ...
at the Battle of Agincourt, 1415.


Cultivation

It is suggested that English parishes were required to grow yews and, because of the trees' toxic properties, they were grown in the only commonly enclosed area of a village – the churchyard. The yew tree can often be found in church graveyards and is symbolic of sadness. Such a representation appears in Lord Alfred Tennyson's poem "
In Memoriam A.H.H. The poem "In Memoriam A.H.H." (1850) by Alfred, Lord Tennyson, is an elegy for his Cambridge friend Arthur Henry Hallam, who died of cerebral haemorrhage at the age of twenty-two years, in Vienna in 1833. As a sustained exercise in tetrametri ...
" (2.61–64). The yew can be very long-lived. The
Fortingall Yew The Fortingall Yew is an ancient European yew (''Taxus baccata'') in the churchyard of the village of Fortingall in Perthshire, Scotland. Considered one of the oldest trees in Britain, modern estimates place its age at an average of 5,000 years. ...
has been considered to be the oldest tree in Europe, at something over 2,000 years old. Tradition has it that Pontius Pilate slept under it while on duty before 30 AD. This has been topped by a tree in the churchyard of a small Welsh village called St Cynog. It has been dated to 5,000 years old by dendrologist Janis Fry. Such old trees usually consist of a circular ring of growths of yew, since their heart has long since rotted away. The Eihwaz
rune Runes are the letter (alphabet), letters in a set of related alphabets known as runic alphabets native to the Germanic peoples. Runes were used to write various Germanic languages (with some exceptions) before they adopted the Latin alphabet, a ...
is named after the yew, and sometimes also associated with the "evergreen"
world tree The world tree is a motif present in several religions and mythologies, particularly Indo-European religions, Siberian religions, and Native American religions. The world tree is represented as a colossal tree which supports the heavens, thereb ...
, Yggdrasil.


Horticulture

Yews are widely used in landscaping and ornamental horticulture. Over 400 cultivars of yews have been named, the vast majority of these being derived from European yew (''Taxus baccata'') or Japanese yew (''Taxus cuspidata''). The hybrid between these two species is ''Taxus'' × ''media''. A popular fastigiate selection of the European yew (''Taxus baccata'' 'Fastigiata') is often called the Irish yew, illustrating the difficulties with common names. A few cultivars with yellow leaves are collectively known as golden yews.


Chemistry

The
Pacific yew ''Taxus brevifolia'', the Pacific yew or western yew, is a species of tree in the yew family Taxaceae native to the Pacific Northwest of North America. It is a small evergreen conifer, thriving in moisture and otherwise tending to take the form o ...
(''Taxus brevifolia''), native to the Pacific Northwest of North America, and the
Canada yew ''Taxus canadensis'', the Canada yew or Canadian yew, is a conifer native to central and eastern North America, thriving in swampy woods, ravines, riverbanks and on lake shores. Locally called simply "yew", this species is also referred to as ...
(''Taxus canadensis'') of Eastern and Central North America were the initial sources of paclitaxel or Taxol, a chemotherapeutic drug used in breast and lung cancer treatment and, more recently, in the production of the Taxus drug eluting stent by Boston Scientific. Over-harvesting of the Pacific yew for paclitaxel led to fears that it would become an
endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...
, since the drug was initially extracted from the bark of the yew, the harvesting of which kills the tree. On January 18, 2008, the
Botanic Gardens Conservation International Botanic Gardens Conservation International (BGCI) is a plant conservation biology, conservation Charitable organization, charity based in Kew, Surrey, England. It is a membership organisation, working with 800 botanic gardens in 118 countries, who ...
(representing botanic gardens in 120 countries) stated that "400 medicinal plants are at risk of extinction, from over-collection and deforestation, threatening the discovery of future cures for disease." These included yew trees, whose bark is used for the cancer drug paclitaxel. However, methods were developed to produce the drug semi-synthetically from the leaves of cultivated European yews. Those can be sustainably harvested without the need to further endanger wild populations, and the Pacific yew is no longer at risk. The more common Canada yew is also being successfully harvested in northern Ontario, Quebec and New Brunswick, and has become another major source of paclitaxel. Other yew species contain similar compounds with similar biochemical activity. Docetaxel, an analogue of paclitaxel, is derived from the European yew (''Taxus baccata'').


In culture

The yew tree is a frequent symbol in the Christian poetry of
T. S. Eliot Thomas Stearns Eliot (26 September 18884 January 1965) was a poet, essayist, publisher, playwright, literary critic and editor.Bush, Ronald. "T. S. Eliot's Life and Career", in John A Garraty and Mark C. Carnes (eds), ''American National Biogr ...
, especially his '' Four Quartets''.


Species and hybrids

*'' Taxus baccata'' , European yew *'' Taxus brevifolia'' , Pacific yew, western yew *''
Taxus calcicola ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, ...
'' , Asian limestone yew *''
Taxus canadensis ''Taxus canadensis'', the Canada yew or Canadian yew, is a conifer native to central and eastern North America, thriving in swampy woods, ravines, riverbanks and on lake shores. Locally called simply "yew", this species is also referred to as Am ...
'' , Canada yew *'' Taxus chinensis'' , China yew *''
Taxus contorta ''Taxus contorta'', synonym ''Taxus fuana'', commonly known as the west Himalayan yew, is a species of tree in the genus ''Taxus''. It is native to temperate forests of Afghanistan Northern India, Tibet and Pakistan Pakistan ( ur, ), ...
'' , West Himalayan yew *'' Taxus cuspidata'' , Rigid branch yew, Japanese yew *'' Taxus floridana'' , Florida yew *''
Taxus florinii ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, da ...
'' , Florin yew *''
Taxus globosa ''Taxus globosa'', the Mexican yew, is an evergreen shrub and one of the eight species of yew. The Mexican yew is a rare species, only known to be found in a small number of locations in eastern Mexico Mexico (Spanish: México), officia ...
'' , Mesoamerican yew *''
Taxus mairei ''Taxus mairei'', Maire's yew, is a species of conifer in the yew family Taxaceae, native to Nepal, Assam, central and southern China, Hainan, Taiwan and Vietnam. It is extensively harvested for its paclitaxel Paclitaxel (PTX), sold under the ...
'' , Maire yew *''
Taxus wallichiana ''Taxus wallichiana'', the Himalayan yew, is a species of yew, native to the Himalaya and parts of south-east Asia. The species has a variety of uses in traditional medicine. It is currently classified as endangered by the IUCN. Distribution an ...
'' , Wallich yew, East Himalayan yew Fossil (extinct) species *''
Taxus engelhardtii ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, d ...
'' – Oligocene, Bohemia, twig-leaves, similar to ''T. mairei''Kvaček, Z. 1984. Tertiary taxads of NW Bohemia. 1982 Acta Univ. Carol., Geol., Pokorny 4: 471–491. 203–289. ''T. brevifolia'' and ''T. globosa'' var. ''floridana'' thought to evolve from ancestral ''T. globosa'' by loss of stomata and papillae; ''T. canadensis'' recognized in Europe based on leaf fossils from late Tertiary deposits *''
Taxus inopinata ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, d ...
'' – Upper Miocene, leaf, similar to ''T. baccata'' *''
Taxus masonii ''Taxus masonii'' is an extinct species of conifer in the yew family, Taxaceae, solely known from the middle Eocene sediments exposed in north central Oregon. The species was first described from a series of isolated fossil seeds in chert. His ...
'' – Eocene
Clarno Formation Clarno may refer to: Locations * Clarno, Oregon * Clarno, Wisconsin ** Clarno (community), Wisconsin *Clarno Township, Lake County, South Dakota Lake County is a county in the U.S. state of South Dakota. As of the 2020 United States Census, t ...
; Oregon, USA *''
Taxus schornii ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, ...
'' – Miocene, northern Idaho Commonly reported hybrids *''
Taxus × media ''Taxus ''×'' media'', sometimes known simply as ''Taxus media'', is a conifer (more specifically, a yew) created by the hybridization of English yew ''Taxus baccata'' and Japanese yew ''Taxus cuspidata''. This hybridization is thought to have ...
''=''Taxus baccata'' × ''Taxus cuspidata'' *''
Taxus × hunnewelliana ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish bark, lanceolate, flat, da ...
''=''Taxus cuspidata'' × ''Taxus canadensis''


References


External links

{{Taxonbar, from=Q27355 Conifer genera Dioecious plants