5. Yew Berries
Taxus is a genus of yews, small coniferous trees or shrubs in the yew family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of 1–40 m, with trunk diameters of up to 4 m. They have reddish bark, lanceolate, flat, dark-green leaves 1–4 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.
All of the yews are very closely related to each other, and some botanists treat them all as subspecies or varieties of just one widespread species; under this treatment, the species name used is Taxus baccata, the first yew described scientifically.
The most distinct is the Sumatran yew (T. sumatrana, native to Sumatra and Celebes north to southernmost China), distinguished by its sparse, sickle-shaped yellow-green leaves. The Mexican yew (T. globosa, native to eastern Mexico south to Honduras) is also relatively distinct with foliage intermediate between Sumatran yew and the other species. The Florida yew, Mexican yew and Pacific yew are all rare species listed as threatened or endangered.
All species of yew contain highly poisonous alkaloids known as taxanes, with some variation in the exact formula of the alkaloid between the species. All parts of the tree except the arils contain the alkaloid. The arils are edible and sweet, but the seed is dangerously poisonous; unlike birds, the human stomach can break down the seed coat and release the taxanes into the body. This can have fatal results if yew ‘berries’ are eaten without removing the seeds first. Grazing animals, particularly cattle and horses, are also sometimes found dead near yew trees after eating the leaves, though deer are able to break down the poisons and will eat yew foliage freely. In the wild, deer browsing of yews is often so extensive that wild yew trees are commonly restricted to cliffs and other steep slopes inaccessible to deer. The foliage is also eaten by the larvae of some Lepidopteran insects including Willow Beauty.
Yew is an evergreen shrub with soft bright green needles similar to the “Christmas tree.” The berries are soft red capsules with a hard green stone in the center. Eating more than three yew berries can cause vomiting, abdominal pain, dizziness, difficulty in breathing, and changes in your child’s heart rate.
Taxus is possibly from the Greek ‘taxon’, ‘bow’ as a result of the use of its wood to make bows. Persian has ‘tachš’ for ‘bow’. A mummy from the Chalcolithic age, around 4000BC, was found with an unfinished bow made of yew so its use for this purpose goes back much further than the English long bowmen usually associated with it. Common Names and Synonyms are yew, Irish yew and English yew.
All parts, except the flesh of the berries, contain taxin(e) a complex of alkaloids which is rapidly absorbed. Also present are ephedrine, a cyanogenic glycoside (taxiphyllin) and a volatile oil.
Where poisoning does occur, in animals or humans, there may be no symptoms and death may follow within a few hours of ingestion. If symptoms do occur, they include trembling, staggering, coldness, weak pulse and collapse.
Yew is one of the plants where the poison is not destroyed when the plant dies. Thus, branches removed from a yew by high winds or pruning will retain their poison.
Though the berries are harmless, the seed within is highly toxic. Unbroken it will pass through the body without being digested but if the seed is chewed poisoning can occur with as few as three berries.
Most incidents with yew relate to animals though it was eaten, in the 1980s, by four prisoners as a means of suicide. Three of the four succeeded.
The interactive CD-ROM produced by St Thomas’ and Kew Gardens cites a number of case reports all involving ingestion of leaves or bark. In one case it is noted that a nineteen month old child accidentally ingested some plant material. Intact seeds were found in his stools confirming that these are not digested. The child recovered.
Farmers have reported cases of poisoning in cattle when dead yew clippings have been dumped on grazing land. The assumption is that someone clipped a yew hedge in the garden, left the clippings to wither thinking that would render them safe before ‘recycling’ them by dumping them on farmland.
A visitor to the Alnwick Garden Poison Garden talked about his elderly neighbour who, being no longer able to manage it himself, had a group of young people in to tidy up his garden. They trimmed his yews and threw the clippings over the fence into the field at the bottom of the garden where three heifers died after eating the cuttings.
Folklore and Facts
Some years ago, it was found that the taxol found in yew could be used to produce chemotherapy treatments for breast and other cancers. The drug produced in this way is called paclitaxel. (Until someone was kind enough to correct me, I was one of the many people who thought tamoxifen was produced from yew. It is not. Tamoxifen is a synthetic drug.) For some time, large gardens made a point of keeping their yew prunings and passing these to companies to extract the taxol and produce these drugs. This was an expensive process and produced only limited amounts of the drug. Since then, however, it has been discovered that taxol is produced from a fungus that lives in the yew. Other fungi have also been found that are able to be used to produce paclitaxel. With some, artificially brewing is possible and, once that process is scaled up, it should reduce the cost and increase the availability of breast cancer treatments.
Though toxic to most animals, deer do graze on yew and gardeners are advised to avoid growing yew if there is a possibility of deer getting into the garden because it is a favourite food. That said, the list of plants which deer will browse is a very long one and there are reports of poisoning incidents so it may be large amounts are toxic to deer.
The idea that yew was grown in churchyards for making longbows is a myth. Bows were made, primarily, from the trunk of the tree so the tree was destroyed. In addition, yew grown in Britain is too brittle so the famous English longbow was made from wood imported from Europe.
The roots of the yew are very fine and will grow through the eyes of the dead to prevent them seeing their way back to the world of the living.
Yew is very long-lived and, in many cases, the yew tree in the churchyard predates the church so, the church was built round a yew tree because the pagan belief about the roots was so deep-seated.
Its longevity leads to its featuring in tales of reincarnation. If two yews are intertwined it is believed that they grew after yew stakes were driven into the chests of lovers whose relationship appalled their community.
Many place names have their origins in particular trees. York is a corruption of an Anglo-Saxon word meaning ‘the place where yew grows’.
John Gerard quotes Galen and others as saying that the yew is very venomous taken internally and that sleeping under a Yew can cause sickness and oftentimes death. He then dismisses these stories by saying that ‘when I was young and went to school, divers of my school fellows and likewise myself did eat our fills of the berries of this tree and hath not only slept under the shadow thereof, but among the branches also, without hurt at all, and that not one time, but many times’.
Thomas Johnson resolves the difference of opinion between the foreign ancient sources and Gerard by asserting that the yew in England is not poisonous but, in other countries, it is highly venomous.