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Taxus brevifolia (Pacific Yew or Western Yew) is a conifer native to the Pacific Northwest of North America. It ranges from southernmost Alaskamarker south to central Californiamarker, mostly in the Pacific Coast Ranges, but with an isolated disjunct population in southeast British Columbiamarker, most notably occuring on Zuckerberg Island near Castlegar and south to central Idahomarker.

Characteristics

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. In some instances, trees with heights in excess of 20m 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 to impossible to make accurate rings counts to determine a specimens true age. Often damaged by succesion 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.

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 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.

Gallery

Image: PacificYew_7684.jpg|Pacific Yew foliage undersideImage: PacificYew_8544.jpg|Pacific Yew formImage: PacificYew_8538.jpg|Pacific Yew foliageImage:PacificYew_7790.jpg|Pacific Yew mat formImage: PacificYew_8566.jpg|Pacific Yew bark

References



Notes




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