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Taxus baccata

Yew Family [Taxaceae]  

 Flowers on male trees (cones):
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 Flowers on female trees (arils):
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Berries: berryZpossible        berryZred  (aril - female flower, edible flesh, toxic seed)
berry8Jul berry8July berry8Aug berry8Sep berry8Sept


17th June 2014, limestone paving, Gait Barrows, Lancs. Photo: © RWD
A small gathering of older Yew trees on limestone pavement grooving for an Ent moot. Hoooooommmmm Treebeard boooooommmmmmed.

9th July 2008, Gait Barrows, Silverdale, Lancs. Photo: © RWD
A younger tree on limestone paving.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 Female trees bear flowers called arils, containing a single hard seed. To attract birds that eat them, the arils are bright red contrasting strongly with the dark green flat-needle foliage. The inedible seed within them are very poisonous and are safely excreted some distance from the tree to continue propagation elsewhere. The Euonymus shrubs, such as Spindle, Nutmeg and species of Oxalis(such as Wood-Sorrel) also have Arils rather than berries.

Undersides of leaves.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 The scarlet-red aril has a near-circular hole through which shows the blackish seed cone. Undersides of leaves.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 Initially, the darker-green female seed cone looks like a small acorn with a lighter-green surround near the base. It develops from the funiculus, which is the attachment point of the seed enveloped by the aril to the stem. This expands and envelops the seed cone turning a scarlet red as it does so. The seed cone is slightly rippled and has a slight bloom.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 The aril expands, turning from green to red until it completely envelops the seed cone.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 Seed cone completely enveloped by the 'flesh' of the aril which has a matt scarlet-red finish. The red aril is thought to have evolved from a primitive cone scale.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 Female plant. This is the base of a seed cone left over after a bird has eaten the edible aril (it wont now develop any further). Undersides of leaves.

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
The underside of the leaves have a slightly raised mid-rib and two edge ribs each side. Between them the leaf is greyish green due to a wax covering which protects the stomata (pores in the leaf epidermis used mainly for transpiration).
[In some species of conifers such as Abies koreana, this wax is much thicker and a bright white colour. The exact position and colour of the stomata is often very useful in identifying conifer species]

5th Oct 2009, ex-Sandhole Mineral Line, Linnyshaw, Gtr Mcr. Photo: © RWD
 Male trees bear flowers commonly called cones but botanically are 'strobilii', which are inconspicuous and initially look like miniature brussel sprout shaped protuberances. Upper sides of leaves are darker, and have a slightly raised mid-rib running down the centreline.

7th March 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
 The underside of the branch contains many male cones.

7th March 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
 Branch twisted 180° to show the cones. Leaves much darker from above (branches behind).

7th March 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
 The male flowers (cones) not yet opened. When open, they will display and shed their pollen, then drop off.

6th March 2015, Peak Forest Canal, Derbyshire. Photo: © RWD
 Male cones droop downwards in profusion.

17th Feb 2015, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
 Male flower cone surrounded by bracts or scales. The globular flower cluster is still to emerge.

6th March 2015, Peak Forest Canal, Derbyshire. Photo: © RWD
 The globular clusters emerge on stalks hidden behind the reddish-brown bracts.

6th March 2015, Peak Forest Canal, Derbyshire. Photo: © RWD
 The male flowers open like tiny irregular suction pads.

27th April 2013, Blackleach Country Pk, Walkden, Gtr M/cr. Photo: © RWD
 Male. The dead remains of male pollen cones having already shed their pollen - standing upright, rather than drooping downwards like the male flowers.

27th April 2013, Blackleach Country Pk, Walkden, Gtr M/cr. Photo: © RWD
 Male flower, now dead, having shed its pollen.

9th July 2008, Gait Barrows, Silverdale, Lancs. Photo: © RWD
Fresh twigs have lighter green leaves.

27th April 2013, Blackleach Country Pk, Walkden, Gtr M/cr. Photo: © RWD
Looking a little like un-opened cones your Author thinks these are new branches where the 'scales' are actually new leaves ready to be spread about the new twig.

13th May 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
New twig and leaf growth.

13th May 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
New twig and leaf growth. Leaves are very pale at first.

13th May 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
Like the old Xmas decorations of old made from rolled-up newspaper which was then cut and pulled out.

13th May 2010, Blackleach Country Park, Walkden, Gtr Mcr. Photo: © RWD
Quite decorative really.

9th July 2008, Gait Barrows, Silverdale, Lancs. Photo: © RWD
The bark is smooth and mottled with shades of brown and grey. Bark often peeling to reveal brownish-red marks underneath. Shoots often appear even on old trunks.

9th July 2008, Gait Barrows, Silverdale, Lancs. Photo: © RWD
Twiglets forming on the bole which at the moment is un-fissured. In later years the bark will develop cracks where potential pathogens could enter. But they will not gain a foothold, for the Yew tree chemical defences are both impeccable and impenetrable.


Taxus baccata 'Fastigiata'

A very popular variant of Yew planted in churchyards and formal gardens

17th April 2009, Church, Kendal, Cumbria. Photo: © RWD
A man-planted specimen. Trunks not often visible, being smothered in branches and foliage. The rounded narrowing tympany shape at the bottom is not, as your Author once assumed, due to pruning, but is natural. It has a very differing stance and jizz to that of Yew. Two unusually upright Yew trees found on an estate in 1765 in County Fermanagh. Cuttings were taken from one of them and a cultivated variety called Fastigiata was produced, from which all other Irish Yews are descended. The original Irish Yew produced still survives in the garden at Florence Court.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The same Irish Yew.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
Another specimen, still shy at revealing its multiple branches at the soil level.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The branches are all directed vertically upwards like a church but one with multiple, albeit very narrow, spires.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
New leaves are a brighter green than the older leaves which are very dark-green, but all on bolt-upright branches.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
At last a specimen not so shy of its partially bare, naked, multiple and branched trunks.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The bark is shinier and more broken up than that of (common) Yew (or perhaps its due more to boys trying to climb it?).

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
New leaves are on bolt-upright stems with paler-green needle leaves also directed upwards in several close bunches.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
Upright, paler-green new needle leaves on their new but so far very short, branches. The older leaves from the main stalk are dark-green and curved over by ~180°.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The leaves have a raised rib on the shiny upperside.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The stems the leaves emerge from ate also ribbed, but multiply; the ribs being where the leaves gradually merge with the stem.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The ribs where the leaves merge with the stem.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
Each new whorl of leaves initially have pale-brown whorls of broader but much shorter leaves which have a white membranous edge. As the leaves grow longer they gradually lose this white edge.

17th April 2009, Church, Seathwaite, Cumbria. Photo: © RWD
The shorter brown leaves with translucent membranous edges. As they grow much longer they will become green and lose their white edges.

21st Oct 2006, Fernilee Church, Whaley Bridge, Derbys. Photo: © RWD
 The arils and leaves of a cultivar of Yew called 'Irish Yew'. The needle leaves are very dark green and curved (or should be, for some reason most here have a pale matte finish atop).

In the more-prostrate form of Yew it is easily confused with : Juniper [a bush with similar height, jizz and leaves, but the leaves of Juniper are sharp at the tip]

Easily confused with : Irish Yew (Taxus baccata 'Fastigiata'), Pacific Yew aka Western Yew (Taxus brevifolia), Chinese Yew (Taxus chinensis) and Japanese Yew (Taxus cuspidata), neither of which are native but still widely planted. There are other Yew trees such as Walking Yew which sheds branches at its periphery and these then root on the ground where they have fallen, creating a slowly extending ring of smaller Yew Trees around a central mature specimen. Other species of Yew include Ground Hemlock (Taxus canadensis) and Western Yew (Taxus brevifolia) which does not seem to contain the alkaloid Taxine.

No relation to Prince Albert's Yew (Saxegothaea conspicua) which looks similar to a Yew tree but belongs instead to the Podocarpaceae family. The Genus Saxegothaea is monotypic, which means there is only one species within the genus.

The Yew tree is evergreen and dioecious, having separate male and female trees each producing the corresponding male or female flower. Male trees produce cones whist female trees produce the red arils containing a single seed.

Skin contact with the sharply pointed Yew leaves (or with the wood) can cause erythema and skin irritation in some individuals, sometimes leading to blisters or even to excessive burns. This is a hypersensitivity response to which not everyone is susceptible, possibly just a relative few individuals.

Yew is widely planted in parks and especially in churchyards and in the grounds of other very old buildings, going back centuries. The Yews in churchyards are usually very old, often pre-dating the present church on the site, for churches were often re-built on previously existing sacred sites. The trunks of old Yews are seldom visible; hidden by a dense mass of branches bearing profuse foliage. They are slow growing, as are most trees that last several centuries. The slow-growing nature lends itself to artistic pruning; many yew trees in church grounds have been shaped by man. With Box trees man is able to take this one level higher; they are able to be pruned into almost any imaginable shape. A Yew in Perthsire is recently suspected of being at least 5000 years old, and possibly up to 9000 years old, which makes it the oldest tree known in the UK, and probably in Europe, and maybe even in the whole World.

Dating Yew trees is particularly difficult as most are hollow in the middle, and therefore counting tree rings will yield only a minimum possible age for the tree, because their annual growth rings rot away in the centre. But sawing a Yew tree down to enable a count of its tree rings is not a viable option. Instead a special drill is use to bore into the centre of the tree which measures the mechanical resistance to boring as it proceeds. Since each years growth contains hard and softer wood, the drill bit encounters a periodic variation in mechanical resistance, and these variations can be counted to yield a minimum age (that is, until the drill bit encounters the hollow centre). It is possible to estimate a Yew trees age by measuring its girth, but this is complicated by the fact that the Yew tree grows slower with age.

It is not possible to use the size of lichens on the bark as an indication of Yew tree age, since neither lichens nor mosses seem able to colonize the bark of Yew trees. This is possibly due to the inhibitory nature of the extensive poisons within most parts of the Yew Tree (apart from the fleshy part of the red arils).

Many old trees become hollow inside, losing the heart-wood, and are better able to withstand the ravages of storms as a result. Since the sap of a tree rises just underneath the bark, the tree really has no desperate need for the inner mart of the wood, and many that have rotted away actually survive longer than those that have not. This must be because, structurally, the stiffness of any object depends more upon its outer circumference than its inner. Getting rid of much of the weight of the tree whilst retaining most of the stiffness seems a good strategy - which structural engineers apply to modern constructions.

In the case of Yew Trees, the wood is permeated by toxic diterpenoids which are mostly anti-fungal. Your Author surmises that, over millennia, these diterpenoids are either changed into less toxic substances or otherwise dissipate, allowing fungi to invade the inner wood and make them hollow.

Yew is a very hard wood due to its slow-growing nature. It has been used to make durable or hard-wearing utilities since antiquity; the oldest known is of a spear found in Clacton-on-Sea which is about 50,000 years old. In the more recent archaeological past it has been used to make yew bows, yew knives and yew bowls. In more modern times it has been used in the industrial revolution to make shuttles for weaving, wooden gears and cogs, pulley wheels and pivots for rotating machinery as well as for lute bodies, combs, pegs, tool handles, wood veneers and religious drinking cups.

The red arils are not berries, but fleshy non-poisonous receptacles for the hard female seed cone within them, which is intensely poisonous. The tree uses the aril to attract birds which feed on the pulpy red surround, depositing the in-edible seed cone elsewhere to propagate the species. The red arils are edible by humans too, but the hard and very poisonous seed cone must not be eaten! Besides the female cones within the arils, there are also male cones nestled near the outgrowth of the leaves on smaller branches; about the size of a black peppercorm these are inconspicuous and look like miniature brussel sprouts. The seeds take about two years to germinate, and the seedling requires deep shade and shelter. The seedling grows slowly so is vulnerable to disturbance and grazing.

The leaves and stems are poisonous to most (if not all) mammals, including humans, but not the fleshy red arils (although the seed cone contained within it is very poisonous). Yew contains a varied cocktail of toxic diterpene Taxanes and Baccatins, the Toxanes block Na+ and Ca2+ channels in heart cells, whilst Taxol and Decetaxel are spindle poisons, inhibiting cell division by preventing microtubules from de-polymerising. Symptoms of poisoning include mydriasis, nausea, vomiting, dizziness, tachycardia, diarrhoea, kidney damage. At first breathing is stimulated and the victim may hyperventilate, leading to acidosis; later breathing is suppressed. Pulmonary spasms follows, then coma and death from respiratory and circulatory failure in just 2 to 24 hours. Treatment is possible. The sawdust produced by sawing or sanding Yew wood should not be inhaled for it too contains toxins. Suicide by ingesting Yew tree leaves used to be a common occurrence. In antiquity Yew was known as the tree of death, and has been used as a poison with which to tip arrows. The dried leaves are more toxic than when fresh and green.

The Fortingall Yew growing in Perthshire, which is thought to be between 2000 to 5000 years old and is surmised to be Britains oldest Yew. It is male (because it produces pollen), but has just recently suddenly started producing berries on one of its upper branches, which means that that part of the tree is now female whilst the rest of the tree still produces pollen with its male flowers. Such sex-changes are not unknown, but are certainly rare.

[The Author speculates:]
This sex-change ability might be viewed as a last ditch strategy to propagate. The tree might be under more stress of late (after all, it is likely that the environment in which it first grew up in thousands of years ago has altered considerably in the intervening millennia and it might think itself now in danger of dying, and thus at risk of losing its genetic make-up forever). This stress may well have encouraged some once-male flowers to change into female flowers. Stress can alter the expression of DNA by epigenetic changes to the DNA (by methylation and/or acetylation) and this may be one mechanism by which flowers can change sex. There are probably many other ways too. When the flowers are mated sexually, some of those methylated genes may find themselves in the seeds (and ultimately the offspring). However, not all epi-genetic changes are heritable (passed on to offspring); many changes are reset at fertilization. But by implication, some are not reset. And these flowers may impart some extra feature to the seedling enabling it to better tolerate the changes that have occurred in its local environment over the last millennia. Although Yew trees do readily propagate vegetatively those seedlings will be clones of the parent. By reproducing sexually any modified germ-cell genes can become incorporated into the offspring (especially if the sex-change was due to genetic or epigenetic changes) which may confer a better ability to tolerate changes in environment.


Taxol, or Paclitaxel, was first discovered in the bark of the rare Pacific Yew Tree (which is not native to the UK) from where it was commercially extracted until a method of laboratory synthesis was devised. It is also present in our Yew. It was found to be a very effective treatment for some cancers, but not all; cancer is not one disease, but many. Taxol stabilises microtubules against disassembly, inhibiting cell division (in both normal growing, and in cancer). It is now marketed under the Generic name Taxol and brand name Paclitaxel. Taxol consists of three condensed rings, one of 4, five of 6 and the other of 8 members. The eight-membered ring, oxetane (shown in blue), is crucial to the drugs activity, as is the benzoyl group (shown in red).


Taxol is just one of possibly seven Taxines and Taxoids (which include Taxine B, IsoTaxine B and Cephalomannine) which are the main toxic pseudo-alkaloids and deadly poisonous constituents of Yew trees.

10-deacetyl Baccatin III was later discovered in the leaves of both the rare Pacific Yew Tree and the much more common Yew. As can be seen, it is more of a basic sub-block, still containing the requisite 8-membered ring (in blue) and the O-benzoyl group (in red). It is now used as a starting compound (from Taxus Baccata only) in the manufacture of both Paclitaxel (Taxol) and Taxotere (Docetaxel), thus saving the rare Pacific Yew tree from assured extinction by over-exploitation.

Cephalomannine, aka Taxol B, is almost identical to Paclitaxel, but part of a phenyl group is missing, shown in green. Cephalomannin was probably first discovered in Cephalotaxus fortunei a species of Yew Tree which in the UK is found only in Pembrokeshire.

Taxine does not have an 8-membered ring as do Taxol, Docetaxel and Baccatin derivatives and Cephalomannine, but instead a 10-membered ring, depicted in magenta. Also, the long side-chain containing the nitrogen atom has swapped allegiance to the opposite side of the multi-membered ring. Several other features are absent too.


Docetaxel, which does not occur naturally, is related to Taxol which does. The only difference between Taxol and Docetaxel is depicted in green, where a -C(CH3)3 is missing and replaced by a H. Again it has the 8-membered ring rather than the 10-membered ring of Taxine. It is manufactured by chemically esterifying 10-deacetyl baccatin III, which is obtained from the leaves of the much more abundant Taxus Baccata (Yew), shown on this page. Docetaxel is marketed under the brand name of Taxotere as a drug to treat breast, prostrate, ovarian, melanomas and lung cancers. The modus operandus is much the same as for Paclitaxel (Taxol) although it appears to be more effective, increasing survival periods by several more months. Thus neither appear to actually cure cancer - but your Author surmises that that might depend on which cancer - there are hundreds of differing cancers.

- the never-ending war

From these alkaloids, it is immediately apparent that synthesis of toxins by plants is not always a well targeted affair, for not only are several intermediate compounds fabricated (as would be expected anyway) but a whole plethora of 'wrongly' assembled molecules are generated in, what must be, a stochastic construction process whereby rings are broken apparently haphazardly or bits are tacked on here and there and other bits chopped off willy nilly. A scattergun approach. Some are indeed programmed in to the genome of the tree to produce, but your Author surmises that not all toxins are pre-programmed into the genes - but rather your Author thinks that some toxins might be produced in error by reacting with other chemicals that are produced within the tree.

Whilst this may seem counter-productive to us, to the plant trying to protect itself from invading pathogens and hungry beasts it matters not - as long as all or most of these compounds are poisonous. In fact, it can be of huge benefit to the plant not to selectively manufacture just one toxin, but instead fabricate a bizarre profusion. The attacking microorganisms or famished creature could, by natural selection, develop resistance to any one specific toxin, but is most unlikely to develop resistance to a huge arsenal of randomly assembled toxins.

This is a strategy which seems to be working, at least in the case of Yew trees: so far no moss or lichen has managed to develop sufficient resistance against taxanes to enable them to colonize the bark of Yew Trees. Although the bark of Yew trees is constantly cracking and is thus vulnerable to attack by fungi waiting to devour the nutritious wood, the Yew tree is able to hold at bay all fungi by means of the toxins it produces. All fungi, that is, bar one... [Read 'A Fungal Infection' below]. Even after millions of years of mammalian evolution, the leaves (and many other parts) of Yew are still toxic to many birds and animals, including humans. Except, of course, the red arils, which the Yew has decided not suffuse with poison but to leave toxin-free for the birds to eat and thence to disseminate its un-digestible seed cargo far and wide in their droppings.

Whilst other plants, although nominally poisonous, may be more toxic, or less poisonous at various times of the year, and under varying conditions:

Plants make poisons to defend themselves against some predator: whether mammal, insect, fungus, rust, or other organism. If that organism is not present, then the plant does not waste its resources making toxins that are not at the moment required. That doesn't mean it is safe to eat then, it may just mean it doesn't produce so much toxin nor such a wide range of similar and dissimilar toxins.

After all, if the plant displayed all of its toxin repertoire all of the time, that gives predators time to acquire resistance to those toxins; best to surprise your enemy when it is least expecting it!

Also, as hinted in the last paragraph, many plants produce a wide plethora of toxins, simply because they can; it might not have 'learned' to produce just the one specified in the poisonous plant book. And why should it; that would be counter-productive, allowing attacking organisms the chance to develop counter-measures. Far better to produce a wide variety of defence chemicals, some based upon the skeleton of the toxin in the book, others on alternative templates belonging to entirely different chemical structures. There is a wide range to chose from including cyanogenic glycosides, coumarins, furocoumarins, pyranocoumarins, steroidal glycosides, terpenoids, sesquiterpenoids, diterpenoids, triterpenoids, polyynes, betaines, tropanes, opiates, quinolines, isoquinolines, taxanes, xanthones, pyrroles, ergot alkaloids, pyridines, pyrrolizidines, iridoids, glucosinolates, tannins, etc. Each species of plant tries to produce those toxins which will best defend it - it doesn't really 'know' which are best - but has had centuries of experimentation to try and produce those which work best for that species of plant. Each species of plant comes to a differing answer; each produces toxins which work best for that particular species as a whole. However, that does not mean that the plant is producing the most efficient toxins or those which work best for it; the experiment in finding the best chemical defence will never end and runs continuously. New toxins might be produced whenever mistakes are made in copying the genome or if the genome is altered by other invading organisms. This sounds very hit and miss, and it is. Another way new varieties or toxins might be produced is when an external organism alters the genome, perhaps inserting some of its own genes or genetic codes. (It has been found that human DNA contains genes or partial genes from many organisms which attack us, including virii. But no one yet knows if they do anything there, either acting positively or negatively - but the pace of research is advancing faster than most folk can keep up). The intended targets of the toxins (other attacking organisms) are also evolving their armoury. The war fought with toxins will never end for either the attacker or the defender - both produce defence and attack armoury.

It is suspected that there are also spooky action-at-a-distance quantum interactions going on in other living organisms too, and these might indeed produce a less random and more targeted product. The two quantum particles involved can 'see' each other well in advance of meeting and they arrange themselves to interact with each other in a more efficient way. It has been shown that these quantum entanglement interactions might be involved in human sight, making the acquisition of photons and the generation of an electron at greater separation distances than is possible without them; increasing the efficiency of our eyes at seeing - which would be especially useful in near darkness. Experiments to measure this enhanced light sensitivity of the eye by observing the quantum entanglement interactions are extremely difficult and cannot be (yet) done in the eye itself. However other experiments in optical laboratories where they beam photons at the complex molecule involved in the sensing of photons in the retina have revealed that this quantum 'spooky action at a distance' (as Einstein once called it) increases the sensitivity to photons by a factor of about two.

There are more than 100,000 toxic substances which plants (of various plant families or genera) produce; and more and more are being discovered all the time by analytic chemists studying plants. These toxins often target specific organisms and many may find use medicinally - in their pure state, not when admixed with the plethora of differing substances any specific plant synthesises. That does not, of course, mean it would not be advantageous for pharmacists to include a plethora of wisely chosen dissimilar toxins to treat a specific condition, for analogous anti-resistance reasons, but they should be chosen by the pharmacist rather than by the plant - the plant only 'knows' how best to defend itself against organisms which attack it - and not from organisms which attack humans.


The Taxol produced by Yew trees is active against a wide-range of fungi that attack wood, apart from one endophytic fungus which has been able to penetrate the toxic alkaloid defences of the Yew tree with impunity. What is even more intriguing is that this fungus also produces Taxol. At first botanists thought that it might be the fungus which supplies Yew trees with their cargo of Taxol, but this was found to be not so; Yew trees lacking the fungus also produce Taxol. This fungus (species of Paraconiothyrium) produces the same toxic metabolite (Taxol) as does its host plant! However, this fungus is actually poisoned by Taxol, and not only produces it itself, but has found a way of secreting it safely away within hydrophobic bodies of the hyphae. This fungus only produces Taxol in response to any other fungus trying to gain entry into the Yew tree, at other times it sequesters the taxol which the Yew tree is producing safely away inside these hydrophobic bodies. The rapidly dividing yew cells on new shoots which have not yet started to protect themselves with Taxol are protected from external fungal attack by this Paraconiothyrium fungus instead. Thus there is a symbiotic relationship between this fungus and the Yew tree which may have been extant for a very long time.

Yew is not the only tree which has a symbiotic relationship with Taxol-producing fungi - some ancient gymnosperm species such as the long-lived Gingo and Wollemia pines which also have this symbiotic relationship. These species have been extant for 100My.

Your Author is still, however, very puzzled by this apparent coincidence of Taxol production. Taxol is a complicated molecule containing 4, 6 and 8 membered carbon rings not to methion all the side groups. He thinks that one or other (Yew or Paraconiothyrium) instigated the synthesis of Taxol, which the other then copied by some means unknown involving evolution perhaps by transfer of genes over the aeons available to them.


 Rhodoxanthin is a keto-carotenoid and symmetrical dimer that is coloured deep-red to purple and which is found in small amounts in several plants, including the Yew tree. Under the e-number E-161f it is used as a food colouring in some parts of the world such as Australia and New Zealand, but not including either the European Union nor the USA. It has two cyclo-hexenone groups at each end of a conjugated chain. It is induced by the action of very strong sunlight on the leaves of Aloe arborescens, which turn a deep red in response. The leaves of several Gymnosperms have a similar reaction to strong sunlight generating Rhodoxanthin.

 Other sources say that Rhodoxanthin is an yellow-orange pigment found in the Autumn leaves of gymnosperms and in the seeds of this species of Yew. So there you have it in black and white: purple is orange-yellow...

It is also present as a colouring in the feathers of some birds, namely Pin-tailed Manakins, which have deep-red feathers (amongst feathers of other colours).

Not to be confused with Rubixanthin, another carotenoid.

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