Taxus baccata L., Yew

Account Summary

Growth form and preferred habitats

A widespread European native and widely cultivated dioecious evergreen tree casting a very dense shade, Taxus baccata L. s.s. (Yew) is one of eight species that formerly comprised T. baccata L. s.l. (Hultén & Fries 1986). The linear leaves are arranged in two lateral ranks and the seed is surrounded by a dull red, fleshy, cup-like edible aril. The Yew tree is unusual for a native conifer, or rather, a 'Taxad', in Britain and Ireland, in being both very slow growing, and also very long-lived (see below). Most particularly, it is unusual through being capable of both vegetative reproduction by layering, in addition to sexual increase and dispersal by seed production (Milner 1992).

It is a small tree in stature when compared with many of its relatives, reaching only a maximum of around 20 m in height, and very often achieving only half this measurement under natural or semi-natural growing conditions. While it is of restricted stature, the Yew can spread its canopy extremely wide in relation to its vertical measurement. On limestone pavement, especially if grazed by goats, Yew can also rarely appear as a prostrate, mat-like shrub.

Sexual reproduction

T. baccata is usually dioecious, having separate male and female trees. Very occasionally, however, monoecious plants are recorded. For instance, an otherwise female tree may bear one or a few branches with small, yellow male cones, rendering the tree monoecious (Nelson 1981; Nelson & Walsh 1993). The female reproductive structure is produced on a short side bud and each consists of an insignificant fleshy disc with a single central ovule (Ross-Craig 1967-70, Part 27, Plate 45; Milner 1992). Pollen release takes place between February and April, wind pollination being the rule, although honey bees do frequently visit male cones to collect the early season pollen that they need to feed their developing brood. Although native Yew trees are hardly all that common, thanks to the frequency of planted specimens the amount of pollen the male trees release is so great that the species is in the top ten plants for pollen abundance in Britain (Milner 1992).

From August to October, the ripe red fruit of the Yew is unmistakable (except possibly for an insect-induced gall that attacks some other alien taxads), consisting of a single, smooth, brownish-purple seed surrounded or embedded in a fleshy, sweet, edible red or pink translucent aril that attracts birds and other animals. (The aril is an outgrowth of the seed coat, which actually is an extra integument layer of the ovule) (Holmes 1979; Lang 1987).

Fermanagh occurrence

T. baccata is one of the very few Fermanagh plant species for which we have records dating before 1800. William Henry recorded it from both the Hanging Rock area and from around Upper Lough Macnean prior to 1739 (Henry et al. 1987). Rutty (1772) also recorded it, "from the islands of Lower Lough Erne". Yew trees, which are certainly native rather than planted specimens, still do occur both on the cliffs and rocky slopes of Hanging Rock Nature Reserve and on the shores and islands of Lower Lough Erne, though there are no recent records from Upper Lough Macnean. Having said that, probably there are more planted Yew trees in Fermanagh than naturally arising specimens, a situation that is now common throughout these islands (Nelson & Walsh 1993).

T. baccata has been recorded from 64 Fermanagh tetrads, 12.1% of those in the VC. As a native species it occurs on the old, pre-drainage shores of Lough Erne and on limestone cliffs and steep scarps in the Monawilkin, Knockmore and Florencecourt areas. Elsewhere, the species has either been planted or is bird-sown in hedges. As the tetrad distribution map shows, it is quite widespread. The Fermanagh Flora Database records include some planted trees in demesnes, gardens and graveyards, together with trees in hedgerows which undoubtedly are bird-sown.

The tetrad map indicates that the main area for the species in Fermanagh lies within the region with limestone soils, particularly around Lower Lough Erne and the upland limestone plateau lying to the south of it. However, the species is not confined to well-drained, lime- or base-rich soils, although it may prefer them, rather it also grows on more acidic terrain. It occurs in mixed deciduous woods over limestone rock, mainly but by no means exclusively associated with ash and hazel.

British and Irish occurrence

While the BSBI's 1962 Atlas attempted to record and display the predominantly native occurrence of Yew in Cumbria, S England and Wales, together with a very thin and mainly coastal occurrence in Ireland (Walters & Perring 1962), the editors of the four year (1996-1999) survey for the New Atlas found that it proved impossible to distinguish native from introduced trees, and consequently they published a map which treats all Yew records as native (Preston et al. 2002). Even with this limitation, while the New Atlas hexad map shows the species widespread throughout the British Isles, it remains most prevalent south of a line between Carlisle and Newcastle, while in Ireland it is thinly scattered throughout (M.E. Braithwaite and M.J. Wigginton, in: Preston et al. 2002).

European occurrence

The Yew tree is sensitive to frost, which limits its northern distribution both in Scotland and elsewhere in W Europe, since it is confined in Scandinavia to southern coastal districts of Norway and Sweden (Jonsell et al. 2000). On the continent it is quite widespread in C and S regions, but strangely absent from most of France, N Germany and Denmark (Jalas & Suominen 1973, Map 194).

Historic timber uses

Yew is the tree most closely linked with history and legends throughout the British Isles. In particular, probably on account of large dimensions and supposed great age, the tree has been associated with notions of immortality and with religious and/or revered burial sites dating back well into Druidical or indeed Neolithic pre-history. Some of the notions associated with the tree continue up to the present day (Mitchell 1996). In early Christian Ireland, Yew was rated in an eighth century law text along with just six other trees as a 'Noble of the wood'. Apparently it rated so highly because Yew wood was the preferred material for domestic vessels, such as eating utensils (Kelly 1997, pp. 380-3). In addition, the timber being extremely hard and both water and insect resistant, it had very many other uses. Yew timber was greatly valued before the use of iron became general, both for its durability and its elasticity. The latter property, for instance, recommended its use for the manufacture of longbow weapons for hunting and in war for well over 300 years (Grieve 1931, p. 866; Milner 1992, pp. 40-3).

In a wide ranging essay extolling the Yew tree, Grigson (1952) discussed how valued the trees were for sheltering dwellings from the prevailing winds. When used in this manner in Fermanagh, they are almost always planted on the SW side and close to the house.

Famous Fermanagh specimens

The story of the 'Florencecourt Yew', T. baccata var. fastigiata, is covered separately below. The other most famous Yew tree in Fermanagh is 'The Crom Yew', or rather 'Yews' in the plural, which probably are the oldest trees of any species in Northern Ireland. Having said this, they are estimated to be only 800 years old at most (Browne & Hartwell 1999). The Crom Yew stands on the eastern bank of Upper Lough Erne near the ruins of Old Crom Castle. The late Alan Mitchell (1996, p. 157), a very well-known tree expert of the second half of the 20th century, gives a very amusing account of 'The Crom Yew', of which he read several descriptions in Irish books and magazines, and examined several drawings of the tree. Accounts of the tree mentioned its extraordinary crown, spread in a low canopy supported by 16 oak posts (and previously by 34 brick pillars), and under whose shelter 200 guests of Lord Erne were once served tea. In 1895, the said Lord wrote that it had a 6 foot [1.83 m] bole, girthing 12 feet [3.66 m] at ground-level, and a spread 77 feet [23.47 m] in diameter. Elwes & Henry (1902) quoted Lord Erne and his "60 supports", and described the tree as, "resembling an enormous green mushroom".

Alan Mitchell visited Crom in 1983, and to his great surprise found not one but two very similar trees, brother and sister, planted about 20 ft [6 m] apart! The trees have had their branches interwoven so that they share the same crown and its supports. The second tree is clearly a twin of its partner, and must have been there for between 400 and 800 years (depending upon which account of its planting you believe). The unsolved mystery must remain why these biological details had been ignored or overlooked in the various accounts of The Crom Yew and by the artists who depicted it? (Mitchell 1996, p. 157). The trees have been 'tidied' in more recent times, and as a result they have lost some of their mystery. It is now easy to get under and through the combined canopy of the two siblings. Browne & Hartwell (1999) provide three photographs in their booklet, but Packenham (1996) has captured their appearance even better in his book Meetings with remarkable trees.

Yew toxicity and seed dispersal

Yew is very poisonous. Indeed, it is claimed that every part of the species except the fruit aril is toxic, but even it may be slightly so (Cooper & Johnson 1998). The fleshy, mucilaginous aril surrounding the seed is eaten by a wide variety of birds, the poisonous seed passing undigested through their intestines and voided with their faeces (Lang 1987). Uneaten fruits remain in good condition for many weeks, but eventually they begin to ferment on the branch. Birds that eat these old, decomposing arils may become intoxicated or ill.

Fruit eating normally reaches a peak in November, and by January only a few, more concealed arils remain on the Yew branches. Members of the thrush family (especially Song Thrushes, Blackbirds and Mistle Thrushes) are the main feeders, but Robins and Starlings are also important. Greenfinches are significant seed-predators, and Great Tits are to a much lesser extent. The Greenfinch has a technique of removing the aril and seedcoat first, before consuming the remainder of the seed, which strongly suggests that the toxins are contained in the testa (ie the seedcoat) (Snow & Snow 1988).

A great deal of study has been carried out on the toxins, a number of which have names based on the genus name. One of the many is 'taxine', which is present in all parts of the tree, and is a complex mixture of at least 11 poisonous alkaloids. Taxine is rapidly absorbed from the digestive tract and interferes with the action of the heart. Another poison is a cyanogenic glycoside called 'taxiphyllin', and there is also an irritant volatile oil. In the last 30 years, a chemically altered alkaloid derivative of taxine extracted from T. baccata leaves, named 'taxol', has proven useful for treating ovarian and breast cancers. Due to a vast effort by biochemists worldwide, taxol can now be efficiently semi-synthesised from Yew leaf hedge clippings.

The toxicity of Yew is not diminished by wilting or drying, so that clippings or even fallen leaves are still highly poisonous (Cooper & Johnson 1998). Yew is considered by some to be the most toxic plant in these islands, yet there are conflicting reports of its toxicity to grazing animals. In general, the trees should always be considered highly toxic, but if eaten regularly or often in small quantities, there may be no adverse effects. Cooper & Johnson (1998) report deer regularly grazing on Yew on the North Downs in Surrey without being poisoned, and we have observed the same thing happening with feral goats in the Burren, Co Clare. Despite these two exceptions, a long list of stock and wild animals are known to have been fatally poisoned, often collapsing and dying within a couple of hours of ingesting a lethal dose, which may be as low as 0.5-2.0 g per kg body weight for animals such as horses (Cooper & Johnson 1998).

Medicinal uses

The fact that Yew is potentially lethal to humans has been known since ancient times, and as with many other poisonous plants, this has somehow led to its medicinal use. It was given to 'steady the heart', and as an antidote for adder bites and against rabies (Cooper & Johnson 1998). As usual, it should be emphasised that NOBODY SHOULD EXPERIMENT WITH POTENTIALLY LETHAL POISONOUS PLANTS.

Most human poisoning with Yew involves children eating quantities of the red arils and the seeds they surround. Provided the poisonous seeds are not chewed, they should pass through the gut harmlessly, or with only minor digestive disturbances being noticed (Cooper & Johnson 1998).

The question of Yew longevity

The longevity of Yew trees and shrubs has been appreciated for hundreds of years, and huge trees are venerated or have even been worshipped in ancient times. However, it has only quite recently been realised that some specimens may be thousands of years old (Milner 1992; Thomas 2000). Unfortunately, the yew trees of greatest girth, and all those over about 400 years age, are invariably hollow (Mabey 1996). For this reason, accurate tree-ring counts or radio-carbon dating of specimen trees are impossible, the early growth wood being absent (Mitchell 1996). Indeed, we do not even know at what age the central heartwood begins to rot, or when and why the trees go into slow-growth mode (Mabey 1996).

Consequently, researchers have turned to documentary evidence, comparing girth measurements and calculated growth rates and annual ring counts of presumed very old and younger trees (Milner 1992). This method of estimating age applied to 70 trees over 300 years old scattered throughout England and Wales, allowed Allen Meredith to calculate that during the first 500 years of growth, a churchyard yew increases in girth an average of 1.1 cm per year until it reaches approximately 5.5 m (A. Meredith, quoted in Milner 1992, p. 82).

However, it is clear from documented measurements made of particular trees, that the accuracy of this method is very suspect, or that many old specimen trees grow much more slowly than this calculation suggests, and in some cases their girth may cease increasing for periods of 300 years or more! Furthermore, Yew is known to be capable of growing without the formation of tree-rings (Thomas 2000, p. 45), and thus, even when accurate ring counts exist, they may provide an underestimate of the real age of the specimen.

The growth of Yew is so irregular, variable and anomalous, that unfortunately no generalised growth curve can be fitted to the data (Mitchell 1996). Dated trees however do exist, for instance that at Dryburgh Abbey, Selkirk, which the monks are known from documentary evidence to have planted in 1136. In 1894, John Lowe measured the girth of this yew to be 11ft 4in [3.45 m], and 90 years later it had added ten inches [25.4 cm] (Mitchell 1996). Thus a tree 858 years old had a girth of 12ft 2in [3.71 m]. Really large old yews may have girths of up to 30ft [9.14 m], but with the known possibility of slowing of the growth rate, and the decay of central wood, we can only guess at their age. As far as we can tell, they are probably several thousand years old. The best account of this interesting but problematic topic appears in Alan Mitchell's Trees of Britain (Mitchell 1996, pp. 153-6).

Variation

The extent to which T. baccata varies is demonstrated by the fact that including the fastigate 'Irish Yew', or 'Florencecourt Yew' (dealt with separately), there are as many as 49 cultivars listed in Dallimore & Jackson (1966) Handbook of Coniferae and Ginkgoaceae. Even allowing for inevitable duplications among cultivated varieties, this still represents a striking array of genetic variation within the species.

Folklore

A considerable body of folklore attaches to the Yew tree, which is conveniently summarised in Grigson (1987), Milner (1992) and Vickery (1995). Several of the folk notions associated with the Yew recounted by these authors might not be all that ancient, but may really have originated from the speculations of the famous late 18th century cleric, Gilbert White, who pondered at length on a specimen in Selborne churchyard (Grigson 1952, p. 12). The Selborne tree was a much measured individual, which unfortunately became uprooted by a gale on 25 January 1990 (Mabey 1996).

Names

The genus name 'Taxus' is probably derived from the Greek 'taxon' meaning 'a bow', the strong, flexible wood having been used for making longbow weapons for centuries. The Latin specific epithet 'baccata' means 'berried', although a better spelling would be 'bacatus' as it is derived from 'baca', meaning 'berry' (Melderis & Bangerter 1955; Gilbert-Carter 1964).

The English common name 'Yew', or 'Yeugh' has various spellings in old authors, for example, 'Ewgh', 'Ewe', 'Ife', 'Ugh', 'Uhe' or 'Uhe tre', 'Vew' and even 'View'. In Anglo-Saxon, it was 'iw', Medieval Latin, 'ivus', 'iva', or 'iua', and there are cognate names in other Germanic languages and in the Celtic languages (Grigson 1974). However, it appears that this Anglo-Saxon name was applied to several different plants (Prior 1879). Some authorities derive the name from Gaelic 'iw', meaning 'green' (ie evergreen), but according to Prior (1879) there does not appear to be any such word. As the current author has no skill in Gaelic, he awaits knowledgeable opinion on this matter. Prior links the Medieval Latin version of the name 'iva', to that of Ivy, and also to 'chamaepitys' (Mediterranean Black Cypress), "through a train of blunders" (Prior 1879), which sums up the confused situation rather aptly.

Yew 'berries' are variously referred to as, 'Snat-berries', 'Snottle-berries', 'Snottergall', 'Snotty-gogs' and 'Snoder-gills', an elegant reference to their sliminess (Prior 1879; Britten & Holland 1886).

Threats

Nowadays, most truly native trees grow on inaccessible cliffs, though some other rare possibly indigenous specimens are browsed by sheep and goats, despite being poisonous.

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