Sometimes the most obvious questions are also the most difficult. They may seem so blatant that after a while they are simply ignored. Like a familiar blemish on a familiar face, they may not bear close examination for fear of causing offence. Or maybe just asking the question seems surprisingly naive, as though to reveal that if you don’t know the answer it diminishes your stature. It is challenging to put your hands up and admit that an answer eludes you. Many people may not even recognise the question. Classical anthropologists were trained to drop their western perceptions when approaching a new tribe, to avoid applying their own values and never to prejudge. They had to think like a Trobriand Islander or Nootka Native American, to get on the inside of their subject of study, to understand their different rules. To approach the kingdom of fungi it may be necessary to abandon everything we know from animals and plants. Is it feasible to think like a fungus, to apply fungal logic, to climb aboard the mycelium for the ride? Even after decades of close encounters with fungi there are apparently simple questions for which I have no matching simple answers. To use conventional principles of natural selection is comparatively uncomplicated in understanding why truffles developed underground, or how fetid gleba benefits a stinkhorn; but other phenomena are elusive. I have already mentioned the mystery of luminescence, but there are more unsolved enigmas. For every thought about these outstanding questions, there is an objection – or perhaps I have not yet learned to think like a mushroom.
Colour. The caps of brittlegills and Amanitas and webcaps can be almost any colour and it is a mystery why. The cap of the Fly Agaric is shameless scarlet, but that of the Destroying Angel virginal white. The Death Cap is livid green, while the Orange Grisette (A. crocea) requires no description. Yellows, browns and greys decorate other woodland Amanita species to complete the palette – but there is no blue. Webcaps (Cortinarius) span the same range, with many bluish or violet species in addition, while the Bloodred Webcap (C. sanguineus) is the most enthusiastic deep red in the whole kingdom. As for the brittlegills, they sport a range of colours to match the full palette of a painter in oils, and even include black, as some species blacken as they age. Just to add to the profusion – or confusion – some brittlegill species can be more than one colour: the Rosy Brittlegill (usually called Russula lepida) is a lovely red coral colour in our woodland – sometimes with an extra splash of the same on the stipe. Another, pale-yellow Russula that grew at the same time under the same beech trees was a puzzle until I realised it was a non-rosy Rosy Brittlegill. It was described as a variety but is regarded as just a colour form. Many Russula species have cap colours that are a mix of green and purplish tones. Others are reliably coloured in the same shades at all times. Those brought up with orchids, birds and butterflies are conditioned to accord importance to colour. In animals it is part of the recognition system that helps perpetuate the species – something for natural selection to work on. I cannot see this in the fungi. The pigment is usually concentrated in the skin of the cap (in some webcaps it fully infuses the flesh). Red might be thought a warning colour, as it is in some insects, but that is implausible in fungi. Slugs chomp into red fungi with the same enthusiasm they give to brown ones or even green Death Caps. I have often observed that they start with grazing the gills, and I suspect (to anthropomorphise) that the fungus might not care, or might even welcome the attention as an aid to spreading its spores through the forest. It has been estimated that an ordinary gilled mushroom can release thirty thousand spores every second, but this is completely unrelated to the pigmentation of the cap – the brightest and the dullest drop their tiny propagules at the same rate. The same puzzles could be rehearsed with regard to the fungus’s edibility for humans – the species that kill us are much appreciated by invertebrates. Flies swarm around the deadliest and the most delicious with equal vigour. Must we assume that the colours of fungi are accidents of metabolism – pigments produced as a by-product of biochemistry, perhaps, dumped into that part of the cap which lies at the outer edge of the developing fruit body? Early mycologists would have had no problem: a plethora of colour was yet another demonstration of the generosity of the Almighty, painter and creator. This sits ill with what has been termed the ‘adaptationist paradigm’, where any hereditable feature deserves examination for its role in the life of the organism. Try as I might, I cannot construct a hypothesis to take on the beautiful dabs of colour that are splashed over the forest floor in due season.
Rarity. The majority of larger fungi are uncommon or rare. A glance through some of the more comprehensive identification handbooks shows how few fungi are described as common or very common. Some species are quite extraordinarily rare – and many of these are large enough not to be readily overlooked, rather than being one of the legion of small brown mushrooms it would be easy to pass by without noticing. The Umbrella Polypore (Polyporus umbellatus) presents a spectacular collection of dozens of little grey caps with pores beneath that form a natural bouquet at the base of beech or oak trees. Anyone who knew anything about fungi couldn’t fail to stop in wonder if they found it, but there are very few UK records each year. It is genuinely rare, though it is so large it must release billions of spores when it fruits. Its fecundity is inversely proportional to its size. The shields (Pluteus) are pretty, pink-gilled toadstools that grow on wood, and one, the pale-brown Deer Shield (P. cervinus) is described as common in all the books. Others are rare, and the beautiful orange Flame Shield (P. aurantiorugosus) is one of the rarest of all, and also unlikely to be missed. It grows out of wood, like all shields, but I have seen it but once in my lifetime. The Italian mycologist Marco Floriani told me of a whole toadstool genus called Musumecia that is quite striking and likely to be spotted; it includes four species known only from one or two collections from Switzerland and northern Italy – and one species from China. This seems almost perversely elusive. After all, the whole purpose of making a fruit body is concerned with survival of the species. Maybe the fungus is commoner somewhere else – this could be the case with the extraordinary Battarrea, which is rare in Britain but quite frequent in desert regions (p. 109), yet it certainly does not apply to polypores and shields. ‘Thinking like a mushroom’, it becomes more plausible that a rare fungus could be paradoxically quite common – but endures as mycelium in soil and only rarely produces a fruit body. It is ‘invisible’. This has been proved by DNA sampling from forest soils, where apparently rare mushrooms can be more prominent underground than they are above it (and vice versa); this applies more particularly to ectomycorrhizal species that can happily bide their time associated with the roots of their hosts until just the right conditions turn up. Even so, it hardly explains why there are hundreds of species of webcaps (dozens of them just associated with beech woods on chalk) and nearly all of them are rarely encountered. Even experienced mycologists are bewildered by their sheer variety. The brittlegills (Russula) are almost as prolific as webcaps. Nor can the ‘invisibility explanation’ be applied to saprotrophs. Many of these fungi are specialists. A large number of species growing only on fire sites are not really rare, because when a fire site turns up and the conditions are right they regularly put in an appearance. But some small dapperling toadstools (Lepiota) and many inkcaps that might appear by any path side turn up very rarely. There is nothing special about the site, but there must be something special about the mushroom. Selfishly, this is a good thing, because every year I see something I have never seen before. It keeps me on my toes. One year I found a very rare, small, but distinctive fungus for the first time on ‘my patch’ in Oxfordshire, only to learn that it had been found all over the south of England at the same time. This is baffling: I cannot explain why so many fungi are rare, nor why they may occasionally break their own rules.
To pick or not to pick. To return briefly to the topic of fungi as food, I like to eat mushrooms, and I have believed that modest consumption of wild food was a reward for a certain expertise. Our mushroom forays[1] were not to be confused with foraging, where the sole purpose is gathering species for the table. I have already described how depressing it is to find woodland trashed by foragers turning over every fruit body in pursuit of Ceps, but this is particularly because I want fungi to be appreciated for their beauty and their interest. Naturalists would be outraged to a woman if wildflower meadows were partially picked and then trampled. I am fully in sympathy with the legislation that now protects our scraps of ancient forests from indiscriminate exploitation. The unanswered question is to what extent picking the fruit bodies affects the future of the species. Again, I find myself perplexed. This book began with a trip to Borgo Val di Taro, where the porcini festival celebrates the abundance of a few delicious species of Boletus. The collecting baskets are still full after hundreds of years. The local mycologists are not worried, and I found my own concerns about picking slipping away. If enough fungi survive to spread their spores the population is not threatened.
This is not the full story. The most wonderful treat for any mycologist, and almost any gastronome, is to discover a mossy bank covered with chanterelles. They erupt like bouquets of exotic, bright-yellow flowers from the ground, and they can be abundant. Yet the figures from Saarbrücken (p. 213) show that the numbers taken to market have greatly declined over recent decades. In the Netherlands, fungi have always been taken seriously, and a study published by the distinguished Dutch mycologist Eef Arnolds in 1991 showed that between 1972 and 1989 species of ectomycorrhizal fungi like chanterelles had drastically declined in controlled study woodland plots to about a third of what they used to be – while the number of fruit bodies per hectare had decreased even more dramatically. Atmospheric pollution (and particularly nitrate pollution) is fingered as the culprit, as even protected habitats have experienced comparable decline. Rain does not recognise fences. It is the same story that I have outlined in the grasslands in my local churchyards, and it is very worrying. Arnolds believes that fungi are the ‘canary in the mine’ in warning of widespread ecological damage. In a far less controlled way, I have noticed lovely mushrooms of no culinary interest disappearing from my local beech woodlands, particularly woodwax (Hygrophorus) species that were once common and are no longer to be seen.
This brings us back to the dilemma about picking. I believe that we can be fairly certain that this activity is not primarily responsible for a decline in numbers of edible species, though it is obviously readily visible compared with pollution and climate change. Pfifferlinge in particular are usually picked after they have had time to release a lot of their spores. There is an odd parallel with the blame attached to schoolboy egg collectors for the decline of common birds in the mid twentieth century. No doubt that played a part, but not compared with the growth of chemical farming and loss of habitat. Only when a bird becomes very rare does the price of the eggs to fanatical collectors rise, and then every egg is important. The benign conditions that succour porcini in northern Italy must have remained relatively unchanged. I am still uncertain about picking, and have settled for the compromise that I will only collect species for the table that are still common, and assume the uncommon ones need every spore they can shed.
Mystery origins. Species have origins. Some evolve because of geographical separation from an ancestral stock; they may occupy different continents, or are found to either side of an oceanic or mountain barrier. Others are the result of genetic mutations that confer some advantage upon them that encourages their spread to new areas, where they might suddenly appear as opportunists in a competitive world. With thousands of species of larger fungi known in Europe, it is inevitable that thousands of matching speciation events must have taken place in the past – but where are they happening now? It is relatively common for a ‘new’ species to appear in Britain, but when the detective work has been done they are discovered to have migrated from elsewhere, often thanks to human agency. The most striking example is probably the Starfish Fungus that was well known in the Antipodes before its appearance in England. On bark-dressed flowerbeds the brilliant-capped Redlead Roundhead (Leratiomyces ceres) is now very common. In my annual talk at the Harcourt Arboretum at Nuneham Courtenay these richly red toadstools become more numerous with each passing year. Twenty years ago I realised that the name that had been applied in the United Kingdom to this fungus was mistaken, and that it was an Australian native that had gone the other way from the ‘ten pound poms’. Many of the microfungi that have caused havoc with our native trees have come in from elsewhere in the world, and sweep through the habitat unchallenged. These case histories are understandable, if sometimes regrettable: strangers find a niche that allows them a foothold in an alien land.
The mystery relates to the hundreds of native species of mushrooms and toadstools of field and forest, many of them rarely encountered. Mycorrhizal fungi include many species that favour the same kind of tree; on our own patch we have cause to wonder at the variety of brittlegills and webcaps that we can find under our familiar beech trees. The growing conditions are apparently similar, even if the weather alters from season to season. These different species must live together in some kind of dynamic equilibrium, with the more uncommon species only occasionally having a ‘good year’ for fruiting. This poses the question of why, how and when they speciated – and should there not be evidence of the appearance of new species, just as there are for new strains of bacteria? I have one possible example among the saprotrophic jelly fungi. Bruce Ing is the veteran expert on slime moulds, a wonderful group of organisms that are not moulds (nor any type of fungus) but can indeed be slimy at an early stage in their growth. In his spare time, he followed the story of one true fungus, the Pale Stagshorn (Calocera pallidospathulata), a jelly basidio which grows in lines out of dead sticks, and finishes up looking like a series of tiny, semi-transparent spoons or table tennis bats – it is easy to recognise. It was first found in 1969 in a coniferous plantation between Pickering and Scarborough, but it was not named as a new species until 1974 by Derek Reid, the expert mycologist who worked at the Royal Botanic Gardens, Kew (where he generously put up with some of my early mistakes). By 1978 it had been collected from twenty-seven sites and had reached Cheshire and Lancashire. The early occurrences seemed to be confined to conifer wood. In two more years it had spread to Wales, and by 1989 it had reached southern England in the New Forest. It managed to outcompete a small, orange jelly, Calocera cornea, which is generally more spike-like, and easily distinguishable. The Pale Stagshorn had reached Norway a year earlier. By this point the species had also consented to grow happily on broadleaved wood. When I led fungus forays in the early 1990s, it nearly always turned up somewhere: clearly, it was a successful invader. I wagged my finger at my small band of fungus enthusiasts as I told the tale of a new interloper. I had hoped that this might be my flagship example of speciation in action, but Bruce Ing reported seeing a similar fungus in Mexico – so invoking once again the principle that evolution always happens somewhere else. Yorkshire would just be a staging post in the story of the Pale Stagshorn. It would be fair to say that it is quite as difficult to import a species to Mexico from Yorkshire as it would be to move one from Yorkshire to Mexico – particularly if their identity is still unproven. But my example of speciation in action is not bombproof. The origins of the thousands of species of mushrooms and toadstools that we are cataloguing have defied attempts to trace them to speciation events in historical time. They are like spooks that appear unannounced from a past that is invisible; they are enigmas. We know from hundreds of molecular studies that species of mushrooms and toadstools are related in hierarchies no different from those of other organisms, which proves that evolution has indeed happened – but apparently not in front of our eyes.
As a postscript, it seems from my recent experience that the Pale Stagshorn is no longer as common a find as it was a decade ago. I feel sure that the little jelly is out there, it is just that I do not meet up with it as often as I used to. Maybe it is jostling into place among the hundreds of other saprotrophs that dine on wood, whatever the initial advantages that helped it spread so widely from a small copse in Yorkshire. This makes just another puzzle to add to the enigma.