Taxus is a genus of yews, small coniferous trees or shrubs in the yew family Taxaceae. They are relatively slow growing and can be very long-lived, and reach heights of 1-40 m, with trunk diameters of up to 4 m. They have reddish bark, lanceolate, flat, dark-green leaves 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.
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 male cones are globose, 3-6 mm diameter, and shed their pollen in early spring. Yews are mostly dioecious, but occasional individuals can be variably monoecious.
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.
The most distinct is the Sumatran Yew (T. sumatrana, native from Sumatra and Celebes north to southernmost China), distinguished by its sparse, sickle-shaped yellow-green leaves. The Mexican Yew (T. globosa, native to eastern Mexico south to Honduras) 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.
All species of yew contain highly poisonous alkaloids known as taxanes, with some variation in the exact formula of the alkaloid between the species. All parts of the tree except the arils contain the alkaloid. The arils are edible and sweet, but the seed is dangerously poisonous; unlike birds, the human stomach can break down the seed coat and release the taxanes 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 Lepidopteran insects including Willow Beauty.
Uses and traditions
Yew wood is reddish brown (with whiter sapwood), and is very springy. It was traditionally used to make bows, especially the longbow. Ötzi, the Chalcolithic mummy found in 1991 in the Austrian alps, carried an unfinished longbow made of yew wood. Consequently, it is not surprising that, in Norse mythology, the god of the bow, Ullr's abode 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.
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, Japanese Yew and the hybrid between them. The most popular of these are the "Irish Yew" (Taxus baccata 'Fastigiata'), a fastigiate cultivar of the European Yew, and the several variants with yellow leaves, collectively known as golden yew.
Taxus baccata is a conifer native to western, central and southern Europe, northwest Africa, northern Iran and southwest Asia. It is the tree originally known as yew, though with other related trees becoming known, it may be now known as the common yew, or European yew.
Taxus brevifolia (Pacific Yew or Western Yew) is a conifer native to the Pacific Northwest of North America. It ranges from southernmost Alaska south to central California, mostly in the Pacific Coast Ranges, but with an isolated disjunct population in southeast British Columbia and south to central Idaho.
It is a small to medium-sized evergreen tree, growing 10-15 m tall and with a trunk up to 50 cm diameter, rarely more.
It has thin scaly brown bark. The leaves are lanceolate, flat, dark green, 1-3 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.
Uses: The chemotherapy drug paclitaxel, used in breast, ovarian and lung cancer treatment, is derived from Taxus brevifolia. As it was already becoming increasingly scarce when its chemotherapeutic potential was realized, the Pacific Yew was never commercially harvested from its habitat in the large scale; the widespread use of the paclitaxel was enabled when a semi-synthetic pathway was developed from extracts of cultivated yews of other species. Unlicenced pharmaceutical production use of closely-related wild yew species in India and China may be threatening some of those species.
Taxus canadensis (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 American Yew or Ground-hemlock. Most of its range is well north of the Ohio River. The southernmost colony known is in the Red River Gorge in Kentucky.
It is usually a sprawling shrub, rarely exceeding 2.5 m tall. It sometimes forms strong upright central leaders, but these cannot be formed from spreading branches, only from the original leader of the seedling plant. The shrub has thin scaly brown bark. The leaves are lanceolate, flat, dark green, 1-2.5 cm long and 1.5 mm broad, arranged in two flat rows either side of the.
The seed cones are highly modified, each cone containing a single seed partly surrounded by a modified scale which develops into a soft, bright red berry-like structure called an aril, open at the end. The seeds are eaten by thrushes, waxwings and other birds, which disperse the hard seeds undamaged in their droppings. The male cones are globose, 3 mm diameter. It is a monoecious plant – one of the few in the genus.
Taxus chinensis is a species of yew. It is commonly called the Chinese yew.
Taxus cuspidata (Japanese Yew or Spreading Yew) is a member of the genus Taxus, native to Japan, Korea, northeast China and the extreme southeast of Russia.
It is an evergreen tree or large shrub growing to 10-18 m tall, with a trunk up to 60 cm diameter. The leaves are lanceolate, flat, dark green, 1-3 cm long and 2-3 mm broad, arranged spirally on the stem, but with the leaf bases twisted to align the leaves in two flattish rows either side of the stem except on erect leading shoots where the spiral arrangement is more obvious. The seed cones are highly modified, each cone containing a single seed 4-8 mm long partly surrounded by a modified scale which develops into a soft, bright red berry-like structure called an aril, 8-12 mm long and wide and open at the end. The arils are mature 6-9 months after pollination. Individual trees from Sikhote-Alin are known to have been 1,000 years old.
It is widely grown in eastern Asia and eastern North America as an ornamental plant.
Taxus floridana (Florida Yew) is a species of yew, found only in a small area of under 10 km² on the eastern side of the Apalachicola River in northern Florida at altitudes of 15–30 m. It is listed as an endangered species.
Taxus globosa or 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, Guatemala, El Salvador and Honduras, and is listed as an endangered species. The Mexican yew is a shrub that grows to an average height of 4.6m. It has large, sharp light green needles growing in ranks on either side of its branches.
Taxus sumatrana is an evergreen shrub and one of the eight species of the yew. It is found in a number of countries, including Afghanistan, Tibet, Nepal, Vietnam, India, Burma and China, and is known as the Chinese yew. It is typically found at heights ranging from 400-3100m in subtropical forest and on highland ridges. It can also be found conserved in the Taroko National Park in Taiwan and the Ayubia National Park in Pakistan.
Taxus wallichiana (Himalayan Yew) is a species of yew, native to the Himalaya from Afghanistan east to western Yunnan in southwestern China, at altitudes from 2,000–3,500 m.
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