In October the beech woods in the Chilterns are transformed. The leaves are still green, but a cool edge to the breeze betokens change. Late autumn is in prospect, and a few freshly fallen leaves presage what will happen in November, but for now the sun sweeps past the elegant beech trunks to throw shafts of light that penetrate to the forest floor. Mushrooms and toadstools are everywhere. The sun reveals brilliant scarlet caps tucked into mossy banks. White caps shine, dark ones have their disguises unmasked. Under the trees pale funnels (Clitocybe) grow in obvious fairy rings, as if under instruction from a dancing master. White puffballs line the paths. You might think some biological klaxon had sounded instructing all the fungi lurking in the leaf litter to get into their reproductive finery before they miss the dance. Even if they cannot be seen, the air is thick with spores of a hundred different species carried on the lightest breeze through the wood and beyond, over the fields to the next cluster of trees. It is impossible to resist the impression that this day is a celebration of the fungal kind, when mycelium of all sorts gathers its resources to join others of their persuasion in fruiting with abandon.
In some favoured parts of the beech wood half a dozen different species of mushroom are within the compass of an arm’s reach. In 2023 it rained a lot in September, and that was followed by a warm spell in early October, the heat and moisture combining to make the perfect conditions for the spore-dance. Only a few, precious weeks in the year are right for the hidden fungi to announce themselves to the world in their typical attire. They had been there all along, doing their hidden business as mycelium, their true identity concealed in superficially mundane similarity to others, like Clark Kent awaiting the moment to reveal his superpowers (and an appropriate change of costume). To a questing mycologist this is the time of plenty. After walking through the same woods in winter and high summer and failing to see so much as a small brown Scurfy Twiglet (Tubaria furfuracea), suddenly there is an embarrassment of riches. It is difficult to know where to turn. Several of the fungi are old friends of a good size and do not need to be disturbed to be identified. Where birch trees have grown among the beeches the scarlet Fly Agaric is invariably present and can be left to continue its business, and the Brown Birch Bolete (Leccinum scabrum) will surely be nearby. The Blackening Brittlegill (Russula nigricans) is often the most abundant of its kind and soon acquires a smoky grey tint that sets it apart from almost all other fungi under the beech trees, and if any doubt remains one example can be turned over to show the very widely spaced gills that distinguish it from all of its relatives. Many other species require closer examination.
This fungal bonanza is a mixture of saprotrophic and mycorrhizal mushrooms and toadstools. The former are breaking down the abundant lying branches and litter in the woodland; the latter are consummating their intimate relationship with the trees under which they are growing. Those bonnets so common on branches and twigs – even on single leaves – are all saprotrophs, as are many other wood recyclers now fruiting on standing trunks or other dead wood. Their location announces what they do in the ecosystem. Species growing on the ground do not identify their habits, and those dining off the leaf litter can be as abundant as mycorrhizal forms: the litter feeders will include all the toughshanks (Gymnopus), inkcaps (Coprinopsis and allies), funnels (Clitocybe and allies), brittlestems (Psathyrella), puffballs (Lycoperdon), stinkhorns (Phallus) and many more. They are the decomposers, guaranteeing the structure of the soil, the recycling of nutrients – I might say the basic health of the habitat. Some of them are mentioned elsewhere in this book. Here I need to focus on the other group, those that forge intimate relationships with the roots of many plants, including trees. These fungi are the mycorrhizal collaborators. They cannot survive without their partners, and the plants that they nurture are equally in debt to the fungi that accompany them though their lives.
Some of the most beautiful fungi are collaborators. This book began with the most famous of them – the Cep (porcini, Penny Bun, etc.). This is the most sought-after of the boletes – those mushrooms resembling agarics in size, shape and texture, but having tubes where a ‘regular’ mushroom has gills. Nearly all of the boletes are mycorrhizal, and some of them are confined to associations with particular trees. Several of them bruise deep blue when they are handled, and none of these should find their way into the pot. There are dozens of different kinds, and the species obliged to grow in association with oaks, birch, pine or larch are sometimes most easily identified by knowing your trees! Because they are partly fed by the resources of a mature tree, it is possible to find boletes early in the year before the main explosion of other fungi. In the deep sunken lanes that are typical of the Weald, in one unusually dry season I found plentiful examples of the handsome (if inedible) white-capped Rooting Bolete (Caloboletus radicans) long before any other mycorrhizal fungi had deigned to put in an appearance. My bolete-obsessive acquaintance goes foraying from July onwards, when most of us have not even thought of dusting off our baskets.
The harlequins of the toadstool world are the brittlegills (Russula). They can dominate some parts of the forest floor, and the cap can be any colour of the rainbow: blue, green, red, yellow, violet; even white or brown. I have mentioned that the Blackening Brittlegill (Russula nigricans) changes from white to black as it ages. While their size range is similar to that of the ‘shop mushroom’, a few are more delicate. Of all the common mycorrhizal fungi, brittlegills paint the woodland with its brightest colours. All of them have white stems with a curious texture: when broken between the fingers they snap suddenly. I liken them to sticks of old-fashioned blackboard chalk. This property is related to the microscopic structure of their tissues, which are made of myriad spherical cells very different from the fibre-like hyphae of typical agarics. The same property makes the gills snap and crumble if stroked – hence the common name. As so often, smell and taste (for the expert) are important identification tools: a tiny nibble is enough if kept on the tongue to see what happens, after which it can be spat out.
The red- and yellow-capped varieties often outnumber other species in my beech wood – the commonest scarlet species is probably the Beechwood Sickener (Russula nobilis), with a taste so hot and peppery that you do not have to wonder about its edibility. A number of generally similar, bright-red brittlegills are there to confuse fledgling mycologists, as they can be very hard to identify. The red coloration might be taken as a warning of taxonomic headaches to come. The Ochre Brittlegill (Russula ochroleuca) commonly provides the yellow tones in autumn woodland, and is not usually very hot tasting, and has a white stipe, but beginners sometimes confuse it with the wholly ochre-coloured Geranium Brittlegill (Russula fellea) with a taste from Hades. Some brittlegill species have confusingly mixed cap colours, mottled purple and green, and the gills and spores vary from white to egg yellow, and the fruit body can smell of Camembert, geraniums, newly baked bread or nothing at all. I am glad I have a friend with a very good sense of smell who can identify some of the more esoteric species; choosing from about two hundred British ones can be tricky. In France, fungus lovers eat those that smell pleasant and taste nutty, without too much regard to taxonomic detail. I would advise caution.
The milkcaps (Lactarius, Lactifluus) are related to the brittlegills and have similar flesh: they are strictly mycorrhizal. They have a feature that identifies them immediately. If the cap flesh or gills are broken, a milky fluid appears almost at once. This milk is not necessarily white – it might be orange, for example – and it may change colour on exposure to air, all of which is important in the identification of species. Most mycologists like milkcaps because there are not too many species to sift through, and they are chunky and well-formed, often with the margins of a concentrically zoned cap slightly rolled under when young. Their colours tend to be more subdued than many of the brittlegills, with various shades of orange-brown, or grey, or green, and, as always, white. With these fungi identification involves tasting the milk, which can be mild and pleasant, or fiercely peppery. The milk of the Fiery Milkcap Lactarius pyrogalus is once tasted, never forgotten. It is an attractive, pallid species with saffron-coloured decurrent gills that is common under hazel (Corylus) trees, to which it is bound in mycorrhizal partnership.
The first time I tested the milk I was simply following a field guide and wanted to make sure I had not made a mistake. White milk leaked prolifically from a damaged gill; I put a drop on my pinky and applied it to my tongue. For a few seconds I had an almost sweet sensation, then it was followed by the most intense combination of heat and pepper I have ever experienced, that seemed to expand beyond the tongue to occupy the whole of my head. Toothache is not dissimilar. Nor did it fade quickly; for at least half an hour I felt the afterburn. Pyro is Greek for ‘fire’ (as in pyromaniac) and galus is milk, so the specific name spells it out. Another common milkcap, associated with birch (Lactarius torminosus), is almost as fierce. It has an attractively zoned cap with pinkish tints and a very hairy margin. I have often found it around young birch trees forming a perfect circle of fruit bodies some distance from the trunk, clearly pointing out its mycorrhizal compass. A curious fact is that it is a popular edible species in Finland. Repeated blanching is supposed to leach out the fire without destroying the crunchy texture, then pickling preserves them, as we might pickle onions. I confess that I have used the taste test for these hot milkcaps to silence unreasonably voluble greenhorn mycologists if I am leading a party through the woods: but it is a ruse that can only be used once per foray. Milkcaps are often choosy about their arboreal partners, with most species of broadleaved trees having a few favoured associated fungi. There are lactarii for willows, alders and oaks. As with the brittlegills, conifers have a different suite of species again.
The Deathcap and most other Amanitas are not quite so choosy, but equally mycorrhizal. I have mentioned some of the common species elsewhere in this book. The scarlet Fly Agaric can be found with many trees, though it seems to like birch best. The Destroying Angel (Amanita virosa) is pure white, and for a long time I believed I had found the only example in Oxfordshire; inexperienced forayers often mistake the white form of the False Death Cap for this lethal beauty. I believed it was very rare until I looked in the birch woods around Ullapool in western Scotland, where I saw troops of these deceptively innocent-looking toadstools. It is one of many fungi that have distributions broadly related to latitude – or rather to the temperature, pollution levels, moisture and other factors that go with it. There are also many milkcaps and brittlegills that prefer glens and the flanks of Monroes to the Home Counties – and who can blame them?
Having both a ring on the stipe and emerging from a volva, Amanita is structurally the most complex of the mycorrhizal agarics, but other groups are equally important in the ecology. Tricholoma species (knights) are a regular find in many woodlands and embrace a collection of mostly robust fungi lacking both ring (there is one exception) and volva, and with white, sinuate gills. Brown, greyish, yellow and white colours predominate, and again there are species that prefer to partner with one tree or another among the thirty or so British species. Some have characteristic odours: I have mentioned Sulphur Knight (T. sulphureum) smelling of tar (p. 61) and Soapy Knight (T. saponaceum) of ‘cheap soap’, while others have pleasant odours of flowers or newly baked bread, as already noted. Some have scaly caps – that is what introduced the Tricho-(Greek for ‘hair’) into the generic name. Whether ‘knight’ is appropriate for the common name is debatable. Many of the more familiar species do have a cap that opens out into a shield shape, with a central boss, but it is hardly unique to these particular fungi.
Most varied and important of all the mycorrhizal agarics associated with trees are the webcaps (Cortinarius), including toadstools that have rust-coloured gills (and spores) at maturity, and range from robust, stately and handsome examples to classic little brown mushrooms (LBMs). The cortina that gives the genus its name and distinguishes it from all other agarics is a cobwebby connexion between the edge of the cap and the stipe, but it can be hard to see once the cap has expanded. It can be coloured in some species. The webcaps can be any shade from white to scarlet, golden yellow, or any conceivable gradation from pale brown to nearly black. Some have striking ‘bulbs’ at the base of the stipe. The colour of the young gills is an essential feature, often violet, yellow or brown. A coloured veil can be present. The cap and stipe are covered in gluten in other species. A sensitive nose will pick up different smells.
Although they may be vital to the life of a tree, the webcaps are a taxonomic jungle. Many mycologists have devoted their lives to ‘sorting’ them, and it is ongoing. Some are easy to recognise: C. violaceus with its dry violet cap, C. sanguineus with its bloody red one, C. armillatus with its orange bands obliquely painted on its elongate stipe. Many others leave the average mycologist scratching their head. Only one species has been regularly eaten, and many more are known to be very poisonous. I am fortunate to have accompanied the doyens of unpaid (but hardly amateur) British webcap expertise, Geoffrey Kibby and Mario Tortelli, on one of those magic autumn days when mushrooms and toadstools are everywhere. I had one particular site in Oxfordshire in mind for them, on the chalk under beech trees – which is known to be where webcaps are particularly happy. It was not disappointing. One species after another was identified with aplomb by my guides. Geoffrey, with his slender, aquiline nose, is sensitive to subtle smells in a way I have been unable to enjoy for many years. He reminds me of a rather fastidious, aristocratic canine as he pokes around the bushes. Mario is taller and more laconic, but equally knowledgeable, and a skilled photographer. There was one unexpected discovery. I had identified a particularly striking large golden-capped webcap as Cortinarius elegantissimus (it does not have a common name, though Most Elegant Webcap would be an obvious tag), but Mario was suspicious that it might be something else. Indeed it was, as the spores were completely different from those of the Most Elegant. Cortinarius bergeronii could be added to the British catalogue of more than three hundred webcap varieties.[1]
Exactly how many species of webcaps there are is now being attacked by sequence analysis of critical segments of their DNA. This may, to be optimistic, at last provide arbitration on the many taxonomic issues that earlier generations grappled with. A monograph published in 2022 devoted to these tricky toadstools was tellingly entitled Taming the Beast.[2] The trouble is that apart from a minority of distinctive species, others blend into one another, or have subtly different flesh reactions with chemicals that had previously proved useful in discrimination, like caustic potash or sulphuric acid. Even Geoffrey Kibby admits that formerly, before the new techniques were available, he only got about three-quarters of his identifications ‘right’. What is clear is that the total number of species recognised is still increasing. The same is true for another mycorrhizal genus, Inocybe – the fibrecaps – with duller gills than the webcaps, and a cap that typically looks as if it had been thatched radially with fine straw. If anything, the discrimination of species is more difficult in this case, because many fibrecaps are small and uncharismatic LBMs, unloved save by a few dedicated enthusiasts. Then we have to add a host of even less conspicuous mycorrhizal fungi, some of them fruiting as no more than hard-to-see white patches on the forest floor. So many species, so much to learn. A cynic might ask: does it matter how many there are, apart from what the poet W.B. Yeats called ‘the fascination of what’s difficult’? It does matter, for surprising reasons.
Mycorrhiza is essential for healthy tree growth. If I dig anywhere under the canopy in our beech wood it does not take long to come across the growing tips of tree roots. They often have a slightly puffy appearance, resembling some finely branched corals; they have a solid feel that is unlike the rootlets of herbs. These tree roots display ectomycorrhiza (ecto – external). Each tree root is covered on the outside by a mantle of fungal mycelium, much as fingers might be encased by tight kid gloves. This is where the collaboration between tree and fungus is enacted. There are other kinds of mycorrhiza, particularly one termed endomycorrhiza (endo-internal), where the fungal interactions occur within the plant cells as finely plumose ‘bushes’ (arbuscular mycorrhiza); this is produced by microfungi very different from the mushrooms and toadstools that are the focus of my story. I will not give it the attention it deserves in nature. The mycelium producing the ectomycorrhiza could belong to any one of the larger fungi that were compatible with that particular tree. In the case of our beech trees, it could be an appropriate brittlegill, milkcap, Amanita, bolete, webcap or fibrecap – or one of many more I have not listed. There must be hefty competition to gain the benefits that follow when a tree root is colonised. This is a collaboration that will be fought for.
The technical term for the fungus-tree partnership is mutualism, a positive symbiosis where both partners benefit. A one-sentence description of the mycorrhizal relationship might be: the fungus partner supplies the tree with water and nutrients, while in return the tree provides the fungus with sugars (and fats) derived from its photosynthetic activities. Both parties share the benefits of sun and soil. The hyphal threads of the fungus scavenge through the ground and the litter. Since hyphae are usually only a few thousandths of a millimetre in diameter, an active network can consist of many thousands, even millions, of tiny, questing interconnected threads. Imagine it as a kind of pervasive mist passing through the soil. The statistics are as hard to grasp as the prodigious numbers of spores produced by a mushroom: a regular claim is that a gram of soil may contain a hundred metres of hyphae. To put it on another scale, in a hectare of forest soil there may be several tonnes of mycelium, much of it belonging to mycorrhizal basidios. This prodigious network allows trees to benefit from the soil on a scale that could never be attained by roots alone.
Although it has been known for many years that fungi obtain nutrients vital for the health of its host, the complex biochemistry of the processes involved has powered many a PhD thesis in more recent years. It is not just a question of picking up useful elements as if they were lying in packets on a supermarket shelf. The most important of these elements are nitrogen, phosphorus, sulphur and iron, all of which fulfil important roles in the growth of healthy plants. The enzyme tool kit of the mushroom is adapted to work on complex molecules in the soil, cutting them down into smaller units that can eventually be absorbed by the roots, charged with valuable gifts. Phosphorus is an essential component in basic biological processes at the cellular level. Sulphur is necessary for the formation of chlorophyll, and thus a sine qua non for photosynthesis, and nitrogen is needed to manufacture amino acids. Iron is not rare in nature – in fact, it is very common as iron hydroxide in many soils – but it cannot be absorbed directly by plants in this form. It has to be wrapped up inside an organic molecule to make a parcel that can successfully be delivered to the roots; fungi have perfected this gift-wrapping at the submicroscopic level. Without iron, photosynthesis cannot prosper and leaves become pallid and die. The fungus partner in turn needs sugars as the fuel that powers the growth of mycelium as new cell walls are required. The exchange of gifts between fungus and tree takes place where the cells of the two organisms are adjacent on the roots. The process might be compared with a customs post between two countries, where protocols have to be observed before passage between different territories can be permitted; the trade runs both ways, through gates, but fluctuates in intensity according to supply and demand. Some gates can only be passed through if a specially designed (molecular) key is applied. If trade ceases, the border can be shut down – or opened up elsewhere. The peaceful forest floor is the site of millions of these unacknowledged transactions, which must continue if the health of the habitat is to be maintained.
When a seedling beech appears in our wood, a pair of opposed, pale-green seed leaves shaped rather like small table tennis bats arise first. Then a shoot pokes out between them; this little shoot has the potential to develop into a new tree and produces the first leaves that look like those of its parent. This seedling would doubtless produce roots to match, tentatively exploring the ground. A mycorrhizal partner would be waiting for this moment. Perhaps a nearby mycelium would attempt to set up a link; or maybe potential candidates would lurk in what has been called the ‘spore bank’ – a stash of fungus spores that can endure within the leaf litter until an opportunity arises. With such a prosperous future in store it seems incontrovertible that competition to make a mycorrhiza with a newcomer would be intense. Equally, a seedling without a mycorrhizal chaperone would be doomed to fail. The odds are probably stacked in favour of fungal partners already on the patch, and these would most likely belong to the nearest mature beech tree. There is good evidence for this. Radioactive tracers have proved that nutrients derived from a nearby tree are transferred through the fungal web to the seedling: and since such seedlings are within a few metres of where the beech nuts drop to the ground there is most likely a genetic relationship between the seedling and the nearby tree. Around a fine old tree there may be many such seedlings that might be helped through their formative years.
You could – if you wished – describe this as the ‘mother tree’ looking after its ‘offspring’. When the old tree eventually dies the ‘offspring’ finally have their chance in the sun, having been nursed in this way through their adolescence. Although the possibility has been mooted since 2009, one book, Suzanne Simard’s 2021 Finding the Mother Tree, took this idea to its apogee, revealing a further agenda in its subtitle – Uncovering the Wisdom and Intelligence of the Forest. The woodland trees are quite like us! This idea had already been popularised in a bestselling 2019 book by a German forester, Peter Wohlleben (The Hidden Life of Trees: What They Feel, How They Communicate). There was no ducking the comparison with human emotions in this book – trees ‘screamed’ as they were being felled, according to his account. The forest was a collection of families. At the same time, the sphere of influence of the mycorrhizal network was growing. It could spread from tree to tree. A whole woodland could be interlinked by a connecting web of mycelium.
Communication channels through this network could pass nutrients to where they might be needed. Information could travel the same way; if nasty beetles arrived in one part of the wood, trees further down the line could be informed so that they could prime their chemical defences. The ‘wood wide web’ was a brilliant phrase to encapsulate what was supposed to be going on beneath the forest floor, a mycological metaphor for the interconnectedness of an ecosystem. It had both timeliness and novelty. Mycologists who for years had been promoting the importance of fungi in nature were now at the popular centre of the action – at last, they were all the rage. It is small wonder that awareness of the wood wide web grew apace, like vigorous and penetrative mycelium. At a time when everyone was being urged to plant trees – for the good of the planet, for the benefits to mental health – ‘tree hugging’, at one time viewed with some suspicion as a hippie eccentricity, became a way of showing sympathy with that ubiquitous web. Animations that are easily accessible on the all-too-human worldwide web portrayed trees with glowing roots sending their beneficence from one neighbour to another. There was something definitely comforting about this model of what goes on in our woodlands. It quickly gained traction.
Scientists should always be on the alert for anthropomorphism – attributing human characteristics to biological processes – and one of the obvious features of the wood wide web was that it was shot through with notions of ‘just like us’. Trees showed their wisdom and intelligence, they had feelings and metaphorically ‘spoke’ to one another. This was more than just a tool to make difficult concepts explicable, it was seductive to investigators, too. The collaboration between unrelated organisms that undoubtedly happens in the mycorrhizal ‘trading station’ had been extended to the scale of whole forests, a kind of salve to Tennyson’s view of ‘nature red in tooth and claw’. Yet there were reasons to be cautious. Rigorous scientific experimental work on wood decay proved that fungi were actively antagonistic to one another at that scale, and in no way collaborative. Although short-distance transfer of nutrients via the mycelium of mycorrhizal fungi had been established experimentally, the longer range had not been fully investigated.
By 2023, some of the scientists who had originally been involved in the wood wide web were urging caution, and a summary in the scientific journal Nature Ecology & Evolution led by Judith Karst laid out the story of how the citation of research had been biased towards www-positive results and was not sufficiently critical. Experiments still needed to be done. The undoubted attractiveness of the idea had led to a lack of rigour. Writing for a lay audience of wood owners in Smallwoods the same year, Professor Katie Field said, ‘Anthropomorphic language can serve as a valuable tool in scientific communication [but] it is crucial to exercise caution and ensure that it does not lead to an oversimplification that compromises accuracy and depth of scientific understanding.’ This is certainly sober language compared with that of the ‘mother tree’. None of these caveats undermine the importance of mycorrhiza in healthy woodland, but it may not play such an interconnected role, or operate on the scale assumed by the wood wide web hypothesis. It says much for the integrity of the scientists that they have raised their own doubts.
As a mere field mycologist, I have to recall what I said about the huge species richness of mycorrhizal fungi, particularly among the agarics. The most prolific genera are linked to living with tree roots: hundreds of species of webcaps (Cortinarius) and fibrecaps (Inocybe), dozens of brittlegills and milkcaps, tens of boletes and knights, and Amanitas, and many more. They are all dependent upon securing that place cuddled up to tree roots where a life of collaboration can begin, a life that can last longer than that of most saprotrophic fungi. There is no doubt that establishing and keeping that posting is competitive. There are different survival strategies among these fungi once they are established; for example, molecular evidence has revealed that some species are much commoner on roots than they are as fruit bodies. It is perfectly possible that the vast number of these mycorrhizal species reflects a matching number of techniques for getting ahead of their rivals, or maybe adapting to very particular niches.
In other branches of biology the kind of enrichment that has happened in the webcaps is known as a ‘species flock’. These are often associated with active speciation, for which competition is an important driver. This does provide a cogent reason for wanting to know as much as possible about these special collaborative mushrooms; all those names do matter. If the wood wide web has anything to recommend it, there must be a change in life strategy from an aggressive mode to a collaborative one once a billet has been safely secured on the roots of beech or birch. All those brittlegills and webcaps and their numerous compatriots are seeking an angle. Perhaps their spores can endure in the soil awaiting their chance. Maybe their mycelium secretes special chemicals that repel rivals. Could this explain why there are so many species on the autumnal forest floor? On the other hand some toadstools – like the Fly Agaric and the Deceiver (Laccaria laccata) – seem to have wider tolerance of different host species, so competition and specialisation cannot be the whole story.
One very odd fungus seems to behave differently. Cenococcum geophilum has been known since 1820, but was named by Elias Magnus Fries in 1827. This species is very common in woods of all kinds where its dark hyphal threads can form links with both conifers and broadleaved trees, so it is unusually catholic in its tastes. The same species is also unusually widespread, having a virtually global distribution. A most peculiar feature of this fungus is that its fruit body remains undiscovered. It appears to lack the culmination of the fungal lifestyle. Molecular studies reveal that it is an asco rather than a basidio, and that it is distantly related to a well-known saprotroph (Glonium) whose very dark fruit bodies look like scabs on wood. What Cenococcum produces for its survival are black, grain-like concentrated capsules of mycelium (sclerotia) that endure in the surface of the forest soil. Being safely enclosed in a wrapping of the black pigment melanin, these capsules protect the fungus so well that they are known to spring back to life after years (some claim centuries) in the soil whenever a new opportunity arises. Since Cenococcum is also host tolerant, it can move from tree to tree – perhaps even from oak to pine and back again – and might even be a possible candidate for moving a single web of mycelium through a stretch of woodland. Whether this develops a channel for sharing resources is another question. If only it could connect one woodland to another across a continent then its reach would be limitless, but who would dare suggest a wwwww (world-wide wood wide web)?
In our woodland in late summer small excavations near the trunks of beech trees are marked by little piles of soil and leaf litter that reveal where some creature has been digging. It must have been after something. Closer examination reveals the characteristic rootlets of beech trees exposed in the sides of the excavation, showing the plump, slightly pinkish appearance of a fungal covering. So whatever was being unearthed must have something to do with roots. Using a child’s toy rake, a nearby patch of litter and old beech nuts can be readily cleared away to reveal the top of the soil layer. Then raking becomes more difficult as the earth is quite flinty, with lots of pebbles that get in the way, but here are the branching roots. What cannot be seen are the yards of fungal hyphae, finer than cobwebs, that must permeate the soil in every direction, feeding nutrients towards the root tips. Then a ‘pebble’ is scratched out of the ground that looks different. It is a finely warty, orange-brown sphere, not much bigger than a glass marble. Within a few minutes three more items of a similar size and colour emerge from beneath the soil layer. This must have been what the diggers were after: truffles, or more precisely False Truffles (Elaphomyces muricatus).
Subterranean fruit bodies: a find with all the thrill of the esoteric. These small brown balls belong to another class of collaborators that never see the light of day. Truffles are as obligatorily mutualist as any brittlegill, but their life is conducted in secret. One of my finds even shows fine mycorrhizal ‘hairs’ on the outside of the sphere. When cut with a sharp knife this small truffle reveals a thick, two-layered skin surrounding a marbled interior where the spores are maturing. It looks a little like an earthball (Scleroderma), but the resemblance is misleading, for the earthballs are basidios whereas Elaphomyces is an asco – the marbled interior is where the asci grow and mature and release their black spores. The puzzle remains about the identity of the animal that made the holes in the ground that showed me where to dig. Elaphomyces are also known as ‘deer truffles’ and it might be presumed that deer find them by smell and eat them. There are indeed deer in my woodland, but I have only seen them browsing; perhaps secretive, small muntjac deer might be able to dig under cover of darkness. Badgers pass through the wood, and have an acutely developed sense of smell (they even sniff out subterranean bee nests) and they are good diggers. The ubiquitous grey squirrels may be interested. The case remains open.
Truffle is a catch-all term for many fungi that develop subterranean fruit bodies. The truffles of gastronomy are species of just one genus among many. Most are ascos, but basidios have also evolved into truffles. The more they are studied, the more it is evident that ‘being a truffle’ is just another life option for fungi, and, such is the endlessly creative ingenuity of the mycosphere, a life below ground has evolved independently many times. This might seem extraordinary: after all, it is like volunteering to bury yourself alive! There are good reasons for this self-interment. Truffles provide many more applicants for the post of ectomycorrhizal partner – adding to what is already a very long list, and in my view increasing competition still further. Developing below ground has several advantages; buried fruit bodies are less prone to suffer from the water loss that often curtails the reproductive lives of their surface cousins, and their favoured potato-like shape is an economical way of packing the greatest number of spores into the smallest possible volume. They do, however, face an obvious problem: how to spread their spores in the absence of any possibility of reaching a breeze. Their cunning ruse is to smell delicious. Wild pigs cannot resist them, and their snouts are the right shape to grub them up. Human beings drool at the first mention of the White Truffle of Italy or the Black Truffle of France. In Australia, subterranean fungi have become the principal food of marsupial mammals like potoroos, and I have seen their diggings that prove it. Whatever-it-is in my wood falls for a similar temptation. The spores pass through the intestinal tract of the guzzler to be spread around the woods; and wild pigs do produce a lot of manure. Rainwater helps the spores to find their roots of choice. The life cycle is renewed.
The Black Truffle, Truffe du Périgord (Tuber melanosporum) is the most commercially important species of Tuber, the genus that includes the gastronome’s objects of desire. It is particularly well known from southern France, but it is not uncommon in Italy and Spain – wherever the Mediterranean climate coincides with a limestone soil and its oak or hazel partners. It was once the basis of a major industry to supply the tables of Paris; in the late nineteenth century up to 1,500 tonnes a year of the precious Tuber were sent from the Midi northwards, often on specially commissioned trains. Since these truffles are black, they must have looked like shipments of coal; but what a cloud of fragrance must have trailed behind! Covered with polygonal warts, and dark, with a mottled interior, they deliver more than they promise from their appearance. The sanglier or wild boar that the penetrating odour evolved to attract still live among the upland scrubby oaks, in spite of the removal of their special foodstuff. By the late twentieth century the truffle yield had declined greatly to about 20 tonnes. Truffles had moved from the quotidian to the recherché. The market price has risen accordingly.
Much is now known about the conditions necessary for the collaboration between truffle and its partner to prosper. The best truffle fruiting happens in association with middle-aged trees in open situations: dense forest is disappointing; young trees have to wait. Although they will never be farmed like mushrooms, seedling trees can be inoculated with mycelium to give them the right partner from the start. Then the nascent trees have to be planted in the correct terrain, but the first crop cannot be harvested until the trees are at least fifteen years old. Truffle farming demands a leisurely state of mind. Climate change is likely to allow the Black Truffle to prosper further north from its traditional range. There is at least one secret site in southern England where inoculated hazel trees are apparently happily living in company with Black Truffle, but it will take fifteen years to know whether the experiment has been successful. If it is, it should be most profitable.
Trained pigs and dogs are still employed to find Black Truffles. These olfactory sleuths smell them out even deep underground. Twenty years ago I joined some trufflers with their dogs in Sardinia. I found it less appealing than I had imagined. The small dogs seemed to be kept dangerously thin, to ensure that they were hungry for the meagre rewards they received from sniffing out the sites where the hidden booty lay concealed. They looked like undernourished strays. The hunters were taciturn, and reluctant to locate a treasure tree in our presence, as if they thought we might sneak back after dark to try to find one for ourselves.
A more appealing version of their trade is to be found in the charming film The Truffle Hunters (2020), which follows the fortunes of elderly Italian fungus seekers, wild of hair and beard, as they tramp through the woods of the Piedmont in search of their fortune. A splendid variety of dogs are their indispensable helpmeets, each one devoted to its master, several of them equally wild of hair, and probably regarded as more important than the wife (if the wife had not already left her obsessive spouse). The hunters are focused upon a truffle even more sought after than the Black Truffle: the White Truffle, Tuber magnatum, the truffle of Alba, which is almost confined to a relatively small area with oaks in Piedmont in northern Italy (it is also known in part of Croatia). As might be guessed from its common name, the fruit body is almost white and smooth; it is often lobed and irregular. These truffles are both rare and hard to find, so the market price is always high. It is debatable whether or not Beluga caviar is the more expensive, but £5,000 for a kilogram of Alba truffle would not be unusual. The odour is extraordinarily intense – the taste is similar – a distillation of everything that is umami, a promise of mouthwatering deliciousness, ripe and many-layered. It is also most penetrating, infusing the atmosphere with its succulence. The chemicals producing its unique perfume are volatile, so the truffle should be eaten as soon after discovery as possible – and very thinly sliced to dress scrambled eggs to make them little short of divine.
Some might say that the fragrance of White Truffle is almost too pungent, insistent, balancing on that delicate point between ripeness and decay. I have had only one close encounter with the famous delicacy in all its glory. In London I was presented with a tiny piece as a gift. I had to take it home wrapped in gauze in a small cardboard box. At that time my commuter train had rather small compartments, holding perhaps a dozen passengers. I had my precious gift in my small briefcase, and it wasn’t long before the confined space of the carriage was infused with umami. Several of my fellow commuters were giving me covert glances. They had clearly identified me as the source of the smell, and I inferred that they thought I must be suffering from some rare variety of body odour. By the time we arrived at Maidenhead station, two of the passengers had alighted and pointedly moved to the next compartment. I was torn between bluffing it out or confessing. The next station was where I got out. As I moved to let myself out of the carriage I uttered a strangled explanation: ‘It wasn’t me. It was the truffle!’ I did not linger to assess the reaction.
The British native is the Summer Truffle (Tuber aestivum). Although still a pleasant addition to an omelette, it is no match for the Périgord or White for intensity of flavour. It looks like a more coarsely warted version of Tuber melanosporum, usually of a size that can be comfortably held in the palm of the hand, and in my experience its companions are beech or hazel, although other trees have been mentioned. It was once more widely appreciated than it is now. John Ramsbottom described how large estates in the nineteenth century employed specialist truffle hunters (and their dogs) to keep the table supplied. In Mushrooms and Toadstools, he records meeting the last professional British truffler, Alfred Collins, who died in 1953, the same year in which Ramsbottom’s New Naturalist book was published. Collins lived in Jubilee Cottage, Winterslow, near Salisbury, where chalk and beech combine to make ideal conditions for underground fungi. Lilian Moody (Alfred’s daughter) recalled her truffling father in The Countryman in 1995. Alfred was the last in a long family line of Collins trufflers, having been taught the skills by his father Eli. He trained his terriers so well that they allegedly jumped over prone rabbits rather than lose the trail of the fungus. ‘When the dogs located a truffle they started scratching the ground above it’, whereupon Alfred employed a special digging spike to retrieve the delicacy. The spike was bequeathed to the Salisbury Museum, where I hope and expect it is still curated. His daughter recalled: ‘On a good day Alfred would gather 25lb of truffles.’ He supplied fresh truffles by post, each package carrying his own postmark to ensure authenticity.
I have crossed paths with Summer Truffles several times. In Savernake Forest, to the east of Marlborough, there are many fine beech trees with clear stretches of leaf litter uncluttered with brambles beneath. I had read that truffles could be located by looking for swarms of trufflivorous (to coin a word) flies that dance above the site of the fruit bodies. Whether by luck or judgement, I did spot numbers of tiny, dancing flies and did indeed find a black Summer Truffle not too far below the surface. This was a long time ago; it was my first subterranean fungus. Many years later a stranger arrived at my door in Henley-on-Thames carrying a plastic box. He had been told that I knew about such things. While cutting a new drainage channel near a hazel in his garden, he had come across these curious, dark concretions in the trench. They were evidently Summer Truffles. I said how interesting they were, but that they would need microscopical examination to confirm their identity if he wouldn’t mind. That evening, we enjoyed a very good omelette.
The doyenne of British scientific truffle hunters is Caroline Hobart. When a fungus foray starts its stately progression through the woods, Caroline quickly identifies a likely tree and settles down on a small rug, leaving the crowd to forge onwards. She often stays put for most of the day. The superficial layer of fallen leaves is brushed aside and then Caroline gets to work with a small rake with flexible teeth (I believe it is a children’s toy). Once she reaches the root zone, the rake is the right size to pick out even small truffles, which may be no bigger than a pea. None of her finds are of culinary interest, but they are all vital to the health of the tree under which she is sitting.
During the course of a day’s work she might easily find half a dozen different species of truffle. On one occasion she pointed out a small, slightly knobbly, pale example that when cut exuded a white, milky juice. This was no asco – in fact, it was a basidio related to the milkcaps I mentioned at the top of this chapter, which release an identical ‘milk’ if any part of the fruit body is damaged. It was another case of a mushroom adopting the underground life and getting closer to the roots that would guarantee its survival. Jackie found a further example in our own wood. We have got used to staring closely at the ground without worrying what passing walkers will think. Although we are dominated by beech, one part of the wood has an understorey of hazel. Near the largest of these trees Jackie noticed one of those scrapes where digging had taken place during the night (animal unknown), and at the bottom of the scrape was a small, brown, spherical object. I recall that she believed it was some kind of animal excretum, but it was very sharp-eyed of her to spot it. I recognised it as a truffle. Furthermore, it was a truffle with an unpleasant smell – quite the reverse of yummy umami. Clearly, not all truffles were there to attract the same animals, and it looked as if this one had been left behind in disgust by whoever dug the hole. I presume the fetid smell was the lure to attract some carrion lover like a crow – or maybe it is true that pigs will eat anything.
In any event, it was a case for Caroline Hobart’s unrivalled memory, and the specimen was duly posted to her in Sheffield. She was pleased to report that my wife’s little truffle was Melanogaster ambiguus, which is much too rarely encountered to have acquired a common name, though you might guess that the Latin translates as ‘black stomach’ – and its interior is indeed coloured dark by its spores. It is another basidio-turned-truffle. This species, however, shares a common ancestor with porcini, with which this book began. It is a bolete that has taken the route underground, doubtless to vie with its terrestrial relatives for space on the roots. In 2020 it was one of many fungi having their molecular sequences determined to reveal their evolutionary origin. It is hard to resist the temptation to anthropomorphise! Spore dropper or spore shooter, every fungus wants to win the race to be the ectomycorrhizal champion. The race took them into the soil, and drove their desire to make the most attractive chemical perfumes. This language would rightly make the purist wince, but maybe can be pardoned for once to explain how the most expensive foodstuff in the world came to be hiding under an oak tree.