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Taxus baccata is a conifer native to western, central and southern Europe, northwest Africa, northern Iran and southwest Asia. Originally and still widely known in English as just Yew, the later discovery of other very similar related species has led to qualification as European Yew, Common Yew or English Yew where detail of which species of Taxus is required.
Additional recommended knowledge
It is a small to medium-sized evergreen tree, growing 10-20 m (exceptionally up to 28 m) tall, with a trunk up to 2 m (exceptionally 4 m) diameter. The bark is thin, scaly brown, coming off in small flakes aligned with the stem. The leaves are lanceolate, flat, dark green, 1-4 cm long and 2-3 mm 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, except on erect leading shoots where the spiral arrangement is more obvious. The leaves are highly poisonous.
The seed cones are highly modified, each cone containing a single seed 4-7 mm long partly surrounded by a modified scale which develops into a soft, bright red berry-like structure called an aril, 8-15 mm 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, waxwings 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 seed itself is extremely poisonous and bitter. The aril is not poisonous, and is gelatinous and very sweet tasting. The male cones are globose, 3-6 mm diameter, and shed their pollen in early spring. It is mostly dioecious, but occasional individuals can be variably monoecious, or change sex with time.
It is relatively slow growing, but can be very long-lived, with the maximum recorded trunk diameter of 4 m probably only being reached in about 2,000 years. The potential age of yews is impossible to determine accurately and is subject to much dispute. There is rarely any wood as old as the entire tree, while the boughs themselves often hollow with age, making ring counts impossible. There are unconfirmed claims as high as 5,000-9,500 years, but other evidence based on growth rates and archaeological work of surrounding structures suggests the oldest trees (such as the Fortingall Yew in Perthshire, Scotland) are more likely to be in the range of 2,000 years. Even with this lower estimate, Taxus baccata is the longest living plant in Europe.
All parts of the tree are toxic, except the bright red aril surrounding the seed, enabling ingestion and dispersal by birds. The major toxin is the alkaloid taxine. The foliage remains toxic even when wilted or dried. Horses have the lowest tolerance, with a lethal dose of 200–400 mg/kg body weight, but cattle, pigs, and other livestock are only slightly less vulnerable. Symptoms include staggering gait, muscle tremors, convulsions, collapse, difficulty breathing, and eventually heart failure. However, death occurs so rapidly that many times the symptoms are missed. The tree should be fenced off or removed from pasture land to prevent grazing animals from consuming it.
The word yew is from Proto-Germanic *īwa-, possibly originally a loanword from Gaulish ivos, compare Irish ēo, Welsh ywen, French if; see Eihwaz for a discussion). Baccata is Latin for bearing berries.
Uses and traditions
In the ancient Celtic world, the yew tree (*eburos) had extraordinary importance; a passage by Caesar narrates that Catuvolcus, chief of the Eburones, literally "farmers of the yew", poisoned himself with yew rather than submit to Rome (Gallic Wars 6: 31). Similarly, Florus notes that when the Cantabrians were under siege by the legate Gaius Furnius in 22 BC, most of them took their lives either by the sword or by fire or by a poison extracted ex arboribus taxeis, that is, from the yew tree (2: 33, 50-51). In a similar way, Orosius notes that when the Gallaecians were besieged at Mons Medullius, they preferred to die by their own swords or by the yew tree poison rather than surrender (6, 21, 1.).
The yew is often found in churchyards from England and Ireland to Galicia; some of these trees are exceptionally large (over 3 m diameter) and may be up to 2,000 years old, though few if any predate the churches they are beside. Many believe that the enormous sacred evergreen at the Temple at Uppsala was a yew. The Christian church commonly found it expedient to take over these existing sacred sites for churches. It is sometimes suggested that these were planted as a symbol of long life or trees of death. An explanation that the yews were planted to discourage farmers and drovers from letting their animals wander into the burial grounds, with the poisonous foliage being the disincentive, may be intentionally prosaic.
Yew is also associated with Wales and England because of the longbow, an early weapon of war developed in northern Europe, and as the English longbow the basis for a mediaeval tactical system. Yew is the wood of choice for longbow making; the bows are constructed so that the heartwood of yew is on the inside of the bow while the sapwood is on the outside. This takes advantage of the natural properties of yew wood since the heartwood is able to withstand compression while the sapwood is elastic and allows the bow to stretch. Both tend to return to their original straightness when the arrow is released. Much yew is knotty and twisted, so unsuitable for bowmaking; most trunks do not give good staves and even in a good trunk much wood has to be discarded.
The trade of yew wood to England for longbows was such that it depleted the stocks of good-quality, mature yew over a vast area. The first documented import of yew bowstaves to England was in 1294. In 1350 there was a serious shortage, and Henry IV of England ordered his royal bowyer to enter private land and cut yew and other woods. In 1470 compulsory archery practice was renewed, and hazel, ash, and laburnum were specifically allowed for practice bows. Supplies still proved insufficient, until by the Statute of Westminster in 1472, every ship coming to an English port had to bring four bowstaves for every tun. Richard III of England increased this to ten for every tun. This stimulated a vast network of extraction and supply, which formed part of royal monopolies in southern Germany and Austria. In 1483, the price of bowstaves rose from two to eight pounds per hundred, and in 1510 the Venetians would only sell a hundred for sixteen pounds. In 1507 the Holy Roman Emperor asked the Duke of Bavaria to stop cutting yew, but the trade was profitable, and in 1532 the royal monopoly was granted for the usual quantity "if there are that many." In 1562, the Bavarian government sent a long plea to the Holy Roman Emperor asking him to stop the cutting of yew, and outlining the damage done to the forests by its selective extraction, which broke the canopy and allowed wind to destroy neighbouring trees. In 1568, despite a request from Saxony, no royal monopoly was granted because there was no yew to cut, and the next year Bavaria and Austria similarly failed to produce enough yew to justify a royal monopoly. Forestry records in this area in the 1600s do not mention yew, and it seems that no mature trees were to be had. The English tried to obtain supplies from the Baltic, but at this period bows were being replaced by guns in any case.
Yews are widely used in landscaping and ornamental horticulture. Well over 200 cultivars of Taxus baccata have been named. The most popular of these are the "Irish Yew" (Taxus baccata 'Fastigiata'), a fastigiate cultivar of the European Yew selected from two trees found growing in Ireland, and the several cultivars with yellow leaves, collectively known as "Golden Yew". A special use of the yew is for topiary garden sculpture, a use not uncommon for many of the more elaborate gardens of England and Scotland.
The precursors of chemotherapy drug Paclitaxel can be derived from the leaves of European Yew, which is a more renewable source than the bark of the endangered Pacific Yew (Taxus brevifolia). This ended a point of conflict in the early 1990s; many environmentalists, including Al Gore, had opposed the harvesting of paclitaxel for cancer treatments. Docetaxel (another taxane) can then be obtained by semi-synthetic conversion from the precursors.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Taxus_baccata". A list of authors is available in Wikipedia.|