Family: Taxaceae
Genus: Taxus
Species: baccata
(i) General background on the plant
Common Yew is a dioecious evergreen tree which can grow to a height of 20 m. Unlike most gymnosperms it is capable of producing leafy branches from the trunk. The thin and scaly bark is reddish brown, and the twigs are green with short stalked leaves 1-3 cm in length, shiny and slightly convex on the upper side. The seeds are approximately 6 mm in diameter and develop singly from the flowers, they are partially surrounded by the fruit which is a bright pinkish red, fleshy, translucent cup. There are many cultivars of common yew available [3]. There are 8-9 closely allied species of Yew differentiated mainly by vegetative characteristics [3].
The plant is found overwhelmingly in cultivation in the UK and is extremely tolerant of cold, heat, shade and sun, wet and drought, urban pollution and any soil pH. It may be killed however in frost hollows during severe winters where temperatures can fall to -25°C or lower. It is also sensitive to soil compaction and heavy metal contamination from action of acid rain [2].
There are other species of Yew, which are very similar to T. baccata, but differ in tolerance of climatic conditions and are found in N.E. USA and Canada eg T. cuspidata and T. media, tolerant of temperatures to at least -35°C [2].
T. mairei however is quite distinct from T. baccata with its sparse yellow-green foliage. It needs very hot and humid summers to grow; its seed does not ripen in northern Europe.
(ii) Details of quality characters
All parts of the tree except the fleshy fruit contain significant concentrations of taxin(e) - a complex mixture of alkaloids that is absorbed rapidly from the digestive tract and interferes with the action of the heart. Yew also contains ephedrine (alkaloid), traces of cyanogenic glycoside, taxiphyllin and a volatile oil. The toxicity of yew clippings is not decreased by wilting or drying. Taxol is extracted from yew clippings and is a complex substance with antitumour activity used in the treatment of breast cancer.
Effects of the Taxus poisoning (mediated by the taxine content) range from: mild nausea to abdominal pain, rapid heart beat, dilated pupils, coma and death. Death results from respiratory and heart failure.
Other constituents of Yew include biflavinoids with Central Nervous System-depressant, analgesic and antipyretic activity [5].
(iii) Current production and yields
A small company was set up in UK in 1995 which collects yew clippings. The clippings are bagged up and kept in cold storage before being shipped to France to be made into the drug Taxol. Taxol is licensed for use in British hospitals to treat women with breast cancer. (10)
(iv) Constraints on production
(v) Markets and market potential
The oil derived from the tree is used for treating breast and ovarian cancer. There may be cultivation methods which allow the oil to be extracted without killing the tree [7]. A testosterone-5a-reductase inhibitor from yew trees for therapeutic use has been patented by a Japanese company. Its discoverer(s) were Suzuki, K.; Imamura, K.; Okajima, T.; Nemoto, M. Patent holder Taisho Pharma Co Ltd (2/8/94).
The timber of yew trees is remarkably strong and durable and was once highly prized in the British Isles for indoor fixtures and fittings. It is also very resistant to decay in wet weather out of doors [3].
(vi) Other information
The tree is a native of woods and scrub land, mainly on limestone, occasionally forming pure woods in sheltered areas on Chalk in the S.E. and limestone in the N.W. of England. It is also tolerant of considerable shade, and is found as far north as Norway [1].
The Yew tree is extremely long lived, being second only to Pinus longaeva, and has specimens with estimated ages of 4000 years [2].
Yew seeds require lengthy scarification and so cultivation by seed is not easy, but good seedlings are possible from seed eaten by birds [2]. Young plants should be transplanted early (8-10 cm high) as Yew forms very thin fibrous roots and does not transplant easily when bigger [2].
Pests and diseases:
Yew scale (an aphid) can severely damage Yew hedges and topiary. A sooty mould feeds on the honey dew exuded by these insects and is usually the first sign of scale attack [3]. Additionally, Yew tree gall midge [8], Ditula angustiorana caused considerable damage to young yew trees in nurseries in Italy in 1981.
See the following pages in the NF-2000 Database
(vii) Contacts
Yew Clippings Ltd. (01308 485693)
(viii) References
1. Clapham, A. R.; Tutin, T. G. & Moore, D. M. (1987) Flora of the British Isles; 3rd Edition. Published Cambridge University Press
2. Huxley, A., Griffiths, M. & Levy, M. 1993 The New Royal Horticultural Society Dictionary of Gardening Macmillan Press Limited, London.
3. Bean, W. J. (1981), Trees & Shrubs Hardy in the British Isles. 8th Edition. John Murray (Publishers) London.
4. Ministry of Agriculture Fisheries and Food 1988. Poisonous Plants & Fungi. An illustrated Guide. Published by HMSO.
5. Frohne, D. & Pfänder, J. (1984) A Colour Atlas of Poisonous Plants Wolfe Publishing Ltd.
6. Jöchle, W. (1962) Biology and Biochemistry of Reproduction and Contraception. Angew. Chem. Internat. Edit. Vol. 1 (1962) no.10
7. Unreferenced Communication from MAFF via Melvyn Askew, ADAS, Woodthorne, Wergs Road Wolverhampton, WV6 8TQ.
8. Svoboda, A. M. (1975) Originality of the Canadian Yew Tree (Taxus baccata) and the occurrence of the yew gall midge (Taxomyia taxi). Cas Slezskeho Muz, Ser C Dendrol 24 (2): 147-152.
9. Lozzia, G. C; Trematerra, P. (1983) Damage caused by Ditula angustiorana on yew trees. Informatore Fitopatologico vol. 33 (4) p.23-25.
10. Greening, J. (1996). Your long yew hedge could help. Farmers Weekly 10 May 1996.