|Chinese Yew - Taxus chinensis |
Family Taxaceae - Yews
Research into Yew chemistry resulted in the discovery
of the now well-known anti-cancer drug taxol.
Taxus wallichiana was found in the late 1960's to yield various compounds useful in treating various forms of cancer in humans, most notably breast cancer. Research into its chemistry resulted in the discovery of the now well-known anticancer drug taxol. The active compound pacilitaxel was first isolated from its bark in 1969. This was followed by development of a drug by the pharmaceutical company Bristol Myers Squibb, subsequently patented under the name taxol. Clinical trials have shown a 56 per cent success rate in treating breast cancer and a 30 per cent success rate in treating ovarian cancer. Taxol taken in combination with other drugs increased the response rate to more than 60 per cent .
Most often found in forests, often among bamboos, frequently by streams; 1100-2500(-2700) m. S Anhui (Huang Shan), Fujian, S Gansu, N Guangxi, SE and W Guizhou, W Hubei, NE Hunan, S Shaanxi, Sichuan, E Yunnan, Zhejiang; cultivated in Jiangxi (Lu Shan) [N Vietnam]." (1)
Evergreen shrub or tree to 14 m tall, wide and bushy when cultivated. Leaves linear-lanceolate, falcate, spirally arranged, spreading in two ranks, about 1.2-2.7 cm. long, 2-2.5 mm. broad, abruptly pointed at the apex, the base decurrent, yellowish green above, pale green beneath. Seeds drupe-like, the fleshy arillate coat reddish at maturity, ripening in the first season. Trunk bark grayish red, exfoliating in irregular flakes and leaving scars with dachytogram-like streaks on the trunk, flakes about 1.5 mm. thick; lenticels inconspicuous; outer bark about 0.4-1.6 mm., membranous or fibrous, with a reddish brown to orange yellow cross-section; phelloderm more or less conspicuous; inner bark 0.5-0.8 cm. thick, pink finely fibrous; freshly cut cambium and newly formed phloem colorless, transparent, becoming pale orange yellow after cutting.
Approximately 10,000 kg of Pacific yew bark are needed to make 1 kg of taxol. The bark of no fewer than six trees is required for a single dose. High demand, combined with such low yields from such a slow-growing tree, could easily result in the decimation of the species. Clearly, alternatives had to be found. It was discovered that taxol could be semi-synthesised from chemical precursors found in the twigs and needles (leaves) of the European yew Taxus baccata (Phillips et al. 1998), which is taxonomically very close to the Himalayan yew and possibly the same species. The harvesting of twigs and leaves is much easier to place on a sustainable basis than the harvesting of bark, which in this species is highly destructive. Use of material from the European yew (Taxus baccata) has taken some pressure off the Pacific yew, but it has also led to over-exploitation of Taxus wallichiana along the Himalayas. Taxus wallichiana has other medicinal uses, both in Ayurveda and Tibetan m edicine. In the latter, it is used to treat fever and relieve muscular pain. The timber is excellent and resistant to decay. It is used to cover graves in Pakistan.
Conservation assessment: The collection of material from various types of yew for the preparation of anti-cancer drugs is ever increasing. It is difficult to distinguish between products deriving from the different species. The population of Taxus wallichiana in China considered to be endangered according to World Conservation Union threat categories. In northern India, where it is estimated that there has been a 90 per cent decline in the population over the last few decades, the species has been listed as critically endangered (WCMC 2002).
It has been possible to synthesise taxol since 1994, but the structure of the molecule is so complex that synthetic production is not yet commercially viable. Pharmaceutical companies still rely heavily on wild sources (Schippmann 2001).
This Chinese Yew was started from a seed 52 years ago.
1. Flora of China
2. USDA NRCS Plant Guide
3. USDA NRCS Threatened and Endangered species
4. USDA, ARS, National Genetic Resources Program. Germplasm Resources Information Network - (GRIN)
5. University of Michigan Native American Ethnobotany
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