|Taxus brevifolia (Pacific Yew) foliage and fruit|
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 isolated disjunct populations in southeast British Columbia (most notably occurring on Zuckerberg Island near Castlegar) and in south to central Idaho.
The pacific yew is a small to medium-sized evergreen tree, growing 10–15 m tall and with a trunk up to 50 cm diameter, rarely more. In some instances, trees with heights in excess of 20 m occur in parks and other protected areas, quite often in gullies. The tree is extremely slow growing, and has a habit of rotting from the inside, creating hollow forms. This makes it difficult and sometimes impossible to make accurate rings counts to determine a specimen's true age. Often damaged by succession of the forest, it usually ends up in a squat, multiple leader form.
It has thin scaly brown bark, covering a thin layer of off-white sap wood with a darker heartwood that varies in color from brown to a magenta/purplish hue. 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.
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 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. It is mostly dioecious, but occasional individuals can be variably monoecious, or change sex with time.
Pacific yew grows in varying types of environments; however, in drier environments it is mostly limited to stream side habitats, whereas in moist environments it will grow up onto slopes and ridgetops. Pacific yew is shade tolerant; however it can also grow in sun. The tree's shade tolerance allows it to form an understory, which means that it can grow along streams providing shade to maintain water temperature.
Traditionally, the wood was used by native Americans to make bows and paddles for canoes, in addition many other items from daily life. The Japanese have also used the wood for decorative purposes.
Discovery of taxol
The chemotherapy drug paclitaxel (taxol), used in breast, ovarian, and lung cancer treatment, is derived from Taxus brevifolia. As it was already becoming scarce when its chemotherapeutic potential was realized, the Pacific yew was never commercially harvested from its habitat at a large scale; the widespread use of the paclitaxel (taxol) was enabled when a semi-synthetic pathway was developed from extracts of cultivated yews of other species. Unlicensed pharmaceutical production use of closely related wild yew species in India and China may be threatening some of those species.
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Media related to Taxus brevifolia at Wikimedia Commons
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