Taxus baccata L.

Kew Species Profiles

General Description

A densely branching evergreen that can live for centuries, the common yew is often found in British churchyards.

Taxus baccata, although native to Britain and sometimes referred to as the English yew, is also found across much of Europe, western Asia and North Africa. The generic name Taxus is reflected in the name of the poisonous taxanes found in the tree. Some botanists did not consider yew to be a true conifer, since it does not bear its seeds in a cone. However, proper consideration of its evolutionary relationships now places the yew family (Taxaceae) firmly within the conifers.

Yew trees contain the highly poisonous taxane alkaloids that have been developed as anti-cancer drugs. Eating just a few leaves can make a small child severely ill and fatalities have occurred. All parts of the tree are poisonous, with the exception of the bright red arils. The arils are harmless, fleshy, cup-like structures, partially enveloping the seeds, which are eaten by birds (which disperse the seeds); however, the black seeds inside them should not be eaten as they contain poisonous alkaloids.

 

Species Profile

Geography and distribution

The common yew is found across much of Europe, western Asia and North Africa. It grows throughout the British Isles (although it is less abundant in Ireland, and absent from the far north of Scotland), especially on calcareous soils.

Ancient yew woods, formed of almost pure stands of yew, are a typical feature of chalk soils in southern England (for example along the North Downs and in the Chiltern Hills).

Description

Taxus baccata is a densely branching, evergreen tree with a massive trunk, reaching up to 20 m tall. The leaves are dark green, linear and up to 3 cm long, with a pointed tip, and appear to spread in two rows on either side of the shoot.

Unlike many other conifers, the common yew does not actually bear its seeds in a cone. Instead, each seed grows alone at the tip of a dwarf shoot, enclosed in a fleshy, usually red, aril which is open at the tip and up to 1 cm in length.

How old is a yew tree?

While it is generally agreed that the yew lives for a long time, the actual age of individual trees is often impossible to judge.

The traditional method of counting the rings in the trunk of a tree is often not an option, because many older specimens develop hollow trunks. This is caused by a fungus that turns the inside of the tree into a pulpy, soil-like mass of rotten wood (which seems to have no ill-effect on the health of the tree as a whole).

However, as yew trunks have been known to reach huge girths of as much as 4 m (13 ft), even the most conservative estimates of around 2,000 years of age, place them as the longest-living trees in Europe. 

Threats and conservation

In the mid 1960s, scientists showed that the taxane alkaloids in yew bark could be used to treat cancer, and the anti-cancer drug Taxol® was approved for use in the 1990s. As a result, there was a rush to harvest bark from Taxus brevifolia (growing in North America) and other yew species. Chemists then found that yew leaves contained compounds that could be used as starting material for the synthesis of paclitaxel, the active anti-cancer compound in the drugs Taxol® and Taxotere®.

While some species of yew have been listed on Appendix II of CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), Taxus baccata remains exempt and is not considered threatened. Nevertheless, the ancient yew woods in England and elsewhere in Europe do merit protection as unique habitats of special interest.

Uses

Widely planted as an ornamental, the common yew is particularly valued for hedging and topiary. There are numerous cultivars, including forms with golden foliage (such as 'Aurea'), upright habit (such as 'Stricta', which is also known as 'Fastigiata' or 'Hibernica', the so-called Irish yew), and compact dwarf forms suitable for a large rock garden.

Taxus baccata has a long association with English culture, not least because its wood was used in making bows. Yew forests were once widespread in Britain but supplies of its timber were soon exhausted, and as long ago as the 13th century yew bow staves were being imported from Switzerland for use in battle. The yew longbow is famous for being the English weapon of victory at the Battle of Agincourt in 1415.

Yews are consistently found in churchyards around Britain and some of these trees are reputedly over 2,000 years old, suggesting that yew may have had some sacred significance in pre-Christian Britain. Without any compelling documentary evidence, this remains mere speculation. Nevertheless, its presence in churchyards has earned yew the nickname 'tree of the dead'.

Kew investigates horse deaths

In 2000, Kew scientists in the Jodrell Laboratory at Kew used their skills in plant anatomy and chemistry to solve the death of two horses. 

Tim Lawrence was able to detect fragments of yew leaves in the stomach contents of the horses while Dr Geoffrey Kite developed a method to detect the toxic yew-derived taxane alkaloids in the stomach contents using liquid chromatography-mass spectrometry (an analytical chemistry technique using physical separation and mass analysis).

Dr Kite has since used his liquid chromatography-mass spectrometry method to investigate other horse deaths, suspected as being caused by yew. 

Millennium Seed Bank: Seed storage

Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.

Description of seeds: Average 1,000 seed weight = 60.3 g. Seeds are dispersed by birds.

Number of seed collections stored in the Millennium Seed Bank: One.

Seed storage behaviour: Orthodox (the seeds of this plant survive drying without significant reduction in their viability, and are therefore amenable to long-term frozen storage such as at the MSB)

Germination testing: 84% germination achieved with pre-sowing treatments (imbibed on 1% agar for 20 weeks at 5°C, then imbibed on 1% agar for 20 weeks at 20°C, then 1% agar at 5°C for 21 weeks) and then on a germination medium of 1% agar, at a temperature of 20°C, on a cycle of 8 hours light/16 hours darkness.

This species at Kew

The parterre in front ofKew Palace is surrounded on all sides by a hedge of common yew. Yew trees can also be seen in the woodland of theConservation Area close toQueen Charlotte's Cottage.

There are some spectacular examples of yew trees growing with their roots climbing down over sandstone rocks at Wakehurst.

Kew at the RHS Chelsea Flower Show 2011

In 2011, Kew partnered with  The Times  to produce a show garden to showcase the significance of plants to science and society.

The garden, designed by Chelsea gold medallist Marcus Barnett, featured species chosen to demonstrate both beauty and utility, including medicinal, commercial, and industrial uses to underline the fact that plants are invaluable to our everyday lives - without them, none of us could live on this planet; they produce our food, clothing and the air that we breathe.

Taxus baccata was one of the species that featured in the garden, which was awarded a Silver Medal.

Distribution

United Kingdom

Ecology

Oak and beech woodland, often on chalk or limestone substrates.

Conservation

Least Concern (LC) according to IUCN Red List criteria.

Hazards

The seeds, leaves and bark are highly poisonous and can cause fatal poisoning of humans and livestock.