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Killer and saviour: the enigmatic 'Taxus'
Humans have long greeted the yew with a mixture of awe and fearful admiration. No doubt this had a lot to do with the fact that the leaves and seeds of the tree were notoriously lethal if consumed. This may not sound like a promising quality in the raw material for a medicine, but the poisonous alkaloid found in 'Taxus baccata' contains some incredibly useful chemicals.
© NTPL / Stephen Robson
Members of the genus 'Taxus' produce compounds known as taxanes, which disrupt microtubule function in our cells. Microtubules are key players in the process of cell division, known as mitosis, so any interference with them prohibits the creation of new cells. This capacity might seem undesirable, but it is invaluable when the cells in question are cancerous and doctors are trying to halt the growth of tumours.
These precious taxanes are most concentrated in the needles of the English yew between the months of May and October, when they are chemically extracted from the clippings, purified, and converted into the chemotherapy drug Taxotere® (docetaxel).
The National Trust is collaborating with Friendship Estates, a family-run farm in Yorkshire that collects the cuttings nationwide and sends them to the Rhône-Poulenc Rorer pharmaceutical laboratory in Essex, where the drug is manufactured. Taxotere was made available in the UK in 1996 and has proven effective in combating lung and prostate cancer, and remarkably successful in the treatment of advanced cases of breast cancer.
© The National Trust / Betsy Anderson
Anticancer drugs derived from yew were first developed in the United States in the 1960s when it was discovered that the bark of the Pacific yew ('Taxus brevifolia') contains a compound called paclitaxel; like all taxanes, paclitaxel was determined to be toxic to cancerous cells. But over-harvesting of paclitaxel led to the scarcity of 'Taxus brevifolia', which was already threatened in the forests of western North America by poor logging practices.
Fortunately, extensive research revealed that an analogous compound (docetaxel) could be isolated from the needles of the common yew, which, as its name suggests, is in no danger of disappearing. Indeed, with tens of thousands of miles of yew hedging stitched across the British Isles alone—and all requiring an annual haircut—'Taxus baccata' clippings have proved a marvellously renewable resource!
The remarkable Yew
Yew is the indispensable backbone of the English garden, and it is easy to see why. Its rich, deep evergreen foliage responds beautifully to trimming, enhances any style of planting, and complements every possible colour. The importance of this versatile plant in formal landscape design cannot be overstated: the same 'Taxus baccata' that so crisply delineates the garden rooms of Hidcote bulges and ripples alongside the terraces of Powis Castle in a massive 18th-century hedge.
© NTPL / Nick Meers
As the topiary tree par excellence, it can also withstand literally hundreds of years of exacting shaping as well as the occasionally drastic shearing, springing to life again and again in such whimsical creations as the Fox and Hounds hedge at Knightshayes (where hunters and hunted are locked in an endless stalemate), or sombrely assembled in a giant topiary representation of the Sermon on the Mount at Packwood House.
The expressive 'Taxus' Apostles, Evangelists, and assembled multitude of Packwood, gathered at the feet—or lower branches, rather—of the lofty Master, echo the religious significance accorded the yew in these islands since the dawn of time. Britain’s fascination with its yew (one of only three conifers indigenous to the country) predates its obsession with gardens, stretching back at least to the time of the Druids, who built their temples in close proximity to the venerable trees. Early Christians erected their churches on the same sacred sites, and to this day 'Taxus baccata' evokes churchyards in the minds of many. Its funerary association is appropriate: the yew remains an ideal symbol for eternal life both because it is evergreen and because it happens to be an exceptionally long-lived tree.
Magnificent Yews
Yews are in fact our longest-living native trees, and revered ancient specimens still dot the landscape. Each has a story to tell, though some are better known than others, such as that of the 2,000-year-old Ankerwyke Yew in Berkshire, which was well into middle-age when King John sealed the Magna Carta at nearby Runnymede in 1215, and Henry VIII is said to have met Anne Boleyn under its boughs in 1530. It must have created a sizeable canopy even then, for today its trunk measures an astonishing 9.4 metres (31 feet) across.
© NTPL / Joe Cornish
Then there are the Crom Castle Yews in Northern Ireland, two trees which have grown together in the past 400 years to give the sprawling appearance, according to one 19th-century observer, of ‘an enormous green mushroom in contour.’
For a more lyrical portrait of 'Taxus baccata' we can turn to Wordsworth, who immortalized four wizened yews on a Cumbrian hillside in his 1803 poem, ‘Yew Trees’. Of ‘those Fraternal Four of Borrowdale’ only three remain (the fourth fell in a great storm in 1883); one of these is large enough to accommodate four people in its hollowed trunk!
A yew will live healthily and happily even when its trunk has been hollow for centuries, and its strong, resilient wood was once prized above all others for fashioning bows—crucial tools of defence well through the Middle Ages until the widespread availability of gunpowder.
From garden to pharmacy
'Taxus baccata' continues to defend us today, this time through its unique chemical composition. This old familiar mainstay of our gardens may not be the first thing that comes to mind when we think of medicinal plants, but it is an important reminder that any plant could contain beneficial compounds only waiting to be discovered by scientists.
National Trust gardens can be considered a vast pharmacopeia, protecting everything from the humble herbs of our medieval ancestors to endangered rainforest species. A staggering proportion of our medicines are plant-derived, lending a critical new dimension to the role of the Plant Conservation Programme at Knightshayes.
© NTPL / David Levenson
So the next time you tour a National Trust garden, imagine the medical potential of the plants around you. Even the household yew, backdrop to our history and garden borders, is now playing a leading role in the recovery of thousands of cancer sufferers. Whether ordinary or rare, creeping or stately, showy or inconspicuous, the plant you pass on the garden path may be more significant than you could imagine.
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