Fungi, being nature’s chemical factories, can be as fragrant as a parfumier’s parlour or as stinky as sewer gas. Since the time of the pioneering mycologists in the nineteenth century it has been known that distinctive smells provide an important clue to identifying species of fungi. I have often wished that I had the olfactory equipment of a hound, for a dog’s dictionary of smells is vastly superior to our own. A canine nose could probably sniff out by smell alone a dozen times as many mushroom species as we can, picking up differences so subtle that a mere hominid would be humbled. We know that a truffle hound can be trained to pick up the evanescent scent of these precious subterranean fungi. I have seen this at work, as the olfactory detective runs over the forest floor, nose down, turning its head this way and that, tail wagging furiously, just waiting to pick up the faintest whiff of fungal gold in order to please its master. However, Homo sapiens has trouble with smells. Even the ‘mushroom smell’ that is so typical of Cultivated and Field Mushrooms is hard to define. The smell reaches sensors in our nose when volatile compounds are released from the mushroom, and then disperse into the atmosphere. At least 150 such special chemicals have been detected emanating from fungi – an airborne cocktail differing from species to species. The chemistry of scent molecules is complicated, although many include eight carbon atoms; their nomenclature is intimidating and need not detain us here; but I cannot resist mentioning that the typical smell of the Cultivated Mushroom is probably down to the molecules 1-octen-3-ol and 1-octen-3-one, the latter in smaller quantity but with more powerful effect, and both derived from fatty acids. Doubtless, a bloodhound could be trained to track them down. Odours are an indispensable prompt for the insects that are obliged to feed on fungi, or lay their eggs on fruit bodies to develop into hungry maggots. With their hypersensitive antennae, many insect species must be able to pick out a favourite food among the rich chaos of smells that hovers over the autumnal woods and fields. They home in on one particular chemical signal, much as a connoisseur might recognise a Château Lafite 1982 among a plethora of inferior red wines.
Most of us humans are not so refined. Our categories are fuzzier. Is it sweet or sour? Pleasant or nasty? Like clean laundry or old socks? We usually have to refer smells to other smells. Almost everyone – there may be mycophobes who would disagree – would describe the ‘mushroom smell’ as wholesome or pleasant, and certainly there is nothing to make the nose wrinkle or the eyes water. But these adjectives don’t really help to run down the essentials of the odour. We have to compare a new fragrance with smells we already know, the bad ones and the good ones: honey or vinegar; burned sugar or rotting meat. Is it a vile stench, or an olfactory blessing? Incense or insult? We are obliged to refer to a short list of familiar smells that we can pinpoint with certainty.
I have led fungus walks for many years, and how to deal with smells continues to be a testing part of the experience because of the idiosyncrasies of people’s olfactory tuning. A handful of species present little difficulty. The Sulphur Knight (Tricholoma sulphureum) is a common toadstool in deciduous woods in the autumn, often fruiting in small troops. It is yellow in all parts – even the widely spaced gills – although the spores are not yellow but white. It has a very strong odour of coal tar, the same smell that emanates from major road repairs as new tarmac is laid down over old before being squashed into place by a steamroller. It is an unmistakable strong pong, and my group all concur with me if I ask them to recall the highway repair scenario. Even Mr Contrarian, who likes to disagree on principle, will agree with the crowd for once. No other toadstool has exactly the same odour, and the diagnosis is supported by its sulphur yellow colour and helpful Latin name. It is hardly necessary to add that it is inedible.
Relatively few mushrooms come up in spring, and several are very good to eat. Some evidence suggests that global warming may be adding species to the list. The all-white St George’s Mushroom (Calocybe gambosa) often appears within a day or two of St George’s Day on 23 April. It is happiest in old grassland rather than woodland, and frequently grows in fairy rings, which can be several metres across. I often find it on roadside verges if they have been mowed, but not too closely. From a distance it can look somewhat like a Field Mushroom. In the hand it is very different. It is an altogether chunkier species with firm flesh and crowded, sinuate gills, which are white and stay white, unlike the pink gills, eventually turning to purple-black, of the Field Mushroom and its relatives. There is no ring on the stem, which can usually be seen on such Agaricus species. St George’s is an unrelated mushroom that just happens to be white (or slightly yellowish) and favours meadows. What gives it away at once is its intense smell, especially if the flesh is rubbed. My old books always say that the odour resembles ‘new meal’ – technically, it is described as ‘farinaceous’, which of course also refers to flour. Very few people visit millers these days, so the old description is sadly redundant. I once made a special trip to an ‘artisan miller’ on the River Thames to check it out. The odour can be rather strong and is certainly not so pleasant as the smell of newly baked bread – some books suggest old, soggy bread is a better match. My fungus beginners usually nod vigorously when the ‘floury’ smell is pointed out to them while a good young specimen is passed around.
Unlike the sulphurous smell of the Knight, the ‘floury’ smell is quite widespread. Life would be simpler if all the ‘floury’ fungi were in a single genus, but instead the capacity to produce this particular smell must have evolved on several occasions. The prolific nineteenth-century mycologist M.C. Cooke was sent a gift of St George’s Mushrooms ‘but the odour was so powerful and oppressive that the house was soon filled with it, and we were compelled to transfer the mushrooms to an outhouse until the hour of sacrifice arrived’. Nonetheless, when the St George’s Mushroom is cooked the more unpleasant notes in the smell diminish markedly, and with its compact, almost crunchy texture it has become a favourite with collectors for the pot. The inhabitants of the Basque country particularly seek it out. St George’s does stay loyal to sites it likes, so those in the know can look forward to late April. My wife Jackie and I struggled to find the perfect complement to its pronounced flavour, and finally came up with a happy marriage. St George’s can stand up to asparagus, and the two combine well in a risotto. It is one of the mushroom dishes on our calendar.
A possible rival for intensity of farinaceous smell is another edible white mushroom, but this time an autumnal one, and it is called the Miller (Clitopilus prunulus), which does not allow much room for doubt about its effect on the nose. It, too, is white, and seems to have a particular liking for the sides of woodland paths. However, it is much more delicate than the St George’s Mushroom, and its cap is often lobed and sometimes a little funnel-shaped. It has a very distinctive ‘feel’ to it. Again, my older books have a good phrase: ‘the feel of a kid glove’. It has a kind of luxurious smoothness, not as slippery as satin, nor yet as tacky as leather. This sort of feature is hard to convey without having the mushroom in front of you; mushroom people become aware of very subtle distinctions. The Miller differs rather obviously from St George’s because its gills (and indeed its spores) are pink, not white, and the soft, thin gills curve to run down along the stem (decurrent). Some people find its mealy taste overwhelming.
Clitopilus prunulus was one of those fungi that everybody thought they knew well – one of those reliable, easy-to-identify mushrooms that could be found on a traipse through the woods most years. I thought it was one of the few mushrooms that would never spring a surprise. But I was wrong. In late 2008, while doing my usual autumnal pottering around beech woodland in the Chilterns, where there were scattered examples of the Miller among the litter, I noticed that these specimens looked unusually robust, perhaps a little convex, and that some were distinctly greyish on top. Even though it seemed such an old friend, I thought I had better confirm my identification under the microscope at home. There is a regular routine to this: I cut off a tiny scrap of the gill edge with a scalpel and put it on a slide, add a drop of water and ‘squidge’ it gently down with a cover slip. The traditional way of doing this is a tap with the rubberised end of a pencil. The effect is to splay out the cells along the gill edge, and dislodge spores. It is quick and effective.
What I saw surprised me: all along the gill edge was a line of minute cylindrical cells – almost making a palisade. These were infertile cells called cystidia – they don’t produce spores, although plenty of spores were being produced along the sides of the gills. I knew that Clitopilus prunulus had a fertile gill edge, so it seemed that what I had before me was a different species of the Miller! This was a greyish, more robust form, which displayed a different gill edge. At this point the amateur scientist writes to the Jodrell Mycological Laboratory at Kew to get help, and help duly came from a learned guru of agarics, Alick Henrici. This strange species had been named already, but only as recently as 1999, by two Dutch mycologists, as Clitopilus cystidiatus. It was then a new species. I believe that my discovery, made walking insouciantly through the woods in South Oxfordshire, was the first time it had been seen in the United Kingdom. Surely this is one of the great rewards of knowing about fungi: you can make discoveries on your doorstep. You don’t have to go up an uncharted tributary of the Amazon to find something new.
I am obliged for ‘health and safety’ reasons to mention another meal-smelling toadstool at this point. The Livid Pinkgill (Entoloma sinuatum) is very rare in my experience; I have only seen it a couple of times in my life. This toadstool is very poisonous and might be confused with the St George’s Mushroom by a novice, since it is also vernal, pale-coloured and robust. I have seen it growing in grassy glades with hawthorn. The only place I have seen the species in quantity is on the island of Sardinia, so maybe it is more prolific in warmer climates. It belongs to a different group of agarics from the St George’s and provides another example of how the fungi throw up ‘lookalikes’ to discombobulate the unwary. However, the spores are pink (as are the gills when mature), so a spore print will readily identify it and provide a clear distinction from the white-spored St George’s. Under a microscope the spores of Livid Pinkgill are also coarsely angular rather than elliptical.
My beginners group gets into more trouble with the False Death Cap, Amanita citrina, a toadstool seen from late summer onwards. Like the Sulphur Knight it is a common toadstool of woodlands – indeed, I have seen the two species growing together. The False Death Cap is an elegant example with a pale lemon-yellow to white cap, and a relatively more impressive, much longer stem than either the Field Mushroom or St George’s Mushroom – in fact the stem is usually longer than the cap diameter, so the latter is held well above the forest floor to spread its spores. In dark, autumnal beech woodland, before the leaves have fallen, the caps sometimes shine as if illuminated by some mystical spotlight from above the litter. When carefully dug from the ground the base of the stem is a perfectly rounded sphere with a sharp upper edge. So one can see where the mushroom arose from an original egg-like ball as its stem elongated: then as the cap expanded, a veil covering the white, free gills split away to leave a ring hanging on the stem. It is a lovely creature, but as its name implies it somewhat resembles the Death Cap. Though it is not deadly, it is far commoner than its lethal relative. And its smell? Our group hums and haws as an example is passed around. ‘It definitely reminds me of something,’ says one young woman helpfully. ‘It’s certainly distinctive and not particularly unpleasant,’ volunteers another. ‘Smells like a mushroom to me,’ says Mr Contrarian. I have my surprising answer ready: ‘Have you ever smelled that curious odour when you cut potatoes?’ This leads to general assent – ‘Yes, that is exactly right, new potatoes, we should have known that all along.’ It seems everyone (except Mr Contrarian) could recognise the smell of the False Death Cap once they had been told what it was. It is a particularly useful character for this one species of the Death Cap family, especially since the Death Cap itself can occasionally ‘wash out’ in the rain to a paler colour. However, the smell could only be precisely diagnosed with reference to another smell.
Poking up from the leaf litter small, graceful ‘bonnets’ (Mycena) invariably abound in woods during the autumn. They, too, have their own smells, but some of the species are so small that the sight of a mycologist apparently trying to stuff a tiny mushroom up her nose is enough to astound any passer-by. Lilac Bonnet (Mycena pura) is one of the commonest species on most forays; with an obtuse pale-purplish cap atop a slender, polished stem, and pale gills, it can form troops under the right conditions. Of course, it has a characteristic smell, best appreciated by slightly bruising the flesh and then sniffing. This time, one of our group gets the distinctive odour quite quickly: radishes. Another finds it to be more like cucumber. Mr Contrarian says it smells like mushroom to him. There is an overall consensus that this small toadstool is of a radishy/cucumbery persuasion and that its smell is consistently present. Since this pretty little toadstool has some of the same poison as Fly Agaric in its tissues, the smell could be taken as a warning: don’t eat me. This radishy smell is quite common among toadstools of several different kinds, and as far as I know is always a warning that its possessor should not go near a frying pan. I have never gone so far as to take radishes into the woods to try out the comparative odour test on the spot. It is enough to attract stares for sniffing small mushrooms let alone waving around a bunch of radishes at the same time. I have my limits.
One odour that nobody gets wrong is aniseed – the powerful aroma of Pernod. The Aniseed Funnel (Clitocybe odora) is an attractive blue-green colour, can be up to a foot across, and has sloping (decurrent) pale gills, often exaggerated by a funnel-like cap. It is possible to find it by smell alone as you walk through the woods. There is another, much less conspicuous Clitocybe (C. fragrans, Fragrant Funnel) that smells almost as strong and usually appears in mossy ground late in the year. Aniseed Funnel is a common species and one I am always glad to see to prove to beginners that not all fungi are hard to identify. Unlike the smells described above, very few fungi have developed the capacity to synthesise anethole, which is the chemical responsible for the aniseed odour. There are a couple of anise smellers, however, growing on trees, Lentinellus cochleatus and the bracket Trametes suaveolens, neither of them common, so the Aniseed Funnel is not unique; the appropriate biochemical toolkit can be geared into action by more than one fungus.
Perhaps more recherché is the smell of coumarin – new-mown hay, or, if you prefer the stronger version, fenugreek. It is a widespread chemical in nature: in our own wood Sweet Woodruff is a prolific herb that develops a lovely fragrance as it dries, reminiscent of sweet vernal grass. This carrier of the coumarin chemical was formerly used to sweeten bed linen, and it must have been rather wonderful to climb in under sheets smelling of new-mown hay. Coumarin is a relatively simple organic compound, and at least one fungus synthesises it as a metabolite. This is a tiny puffball (Phleogena faginea) that grows gregariously on sticks and wood, with short stems supporting a spherical bag of spores, only about three millimetres across. It hardly looks like a regular fungus, but under the microscope its affinities are indisputable. I was delighted to see it once on a cold November day in Suffolk; despite its small size the spicy smell was quite evident. That discovery would not have been made had I not been on a foray with more than a dozen experienced fungus fanciers. One of them had seen the Fenugreek Stalkball before, and that had the extraordinary effect of sharpening his senses for recognising it the next time. It is still not a common sight. Several mushrooms smell of curry as they dry on a window ledge, one unsurprisingly called the Curry Milkcap (Lactarius camphoratus). This is a small red-brown mushroom found in conifer forests, and like all milkcaps it exudes white latex where the flesh is damaged. The smell of the dried fruit body is surprisingly strong: one specimen drying out in the sun can infuse a whole room. It has a relative growing under birch trees that smells of coconut. A good nose is a useful addition to sharp eyes in the search for a full basket of different fungi.
Relatively few fungi have really offensive odours. The phalloids – the stinkhorn and its allies – are mycology’s masters of disgusting smells and deserve more attention below. Most brittlegills (Russula) offer little to offend the nose, but one group of species, centred on the Stinking Brittlegill (R. foetens), smells distinctly of Camembert cheese, or, if you prefer, old socks. In some summers these smelly species are common under the oaks along the Sandlings Walk in Suffolk, and forayers are free to haggle over socks or Camembert to their heart’s content. The conclusion is usually no better than that one person’s cheese is another person’s socks. Whether the smell of kippers is unpleasant or pleasant is a matter of individual taste, but the small, warm-brown toadstool Cucumber Cap (Macrocystidia cucumis) smells very strongly of smoked fish to me, even though both its common and Latin names mention cucumber. Smells, as I have emphasised, are personal.
However, few would quibble with the smell of Gymnopus brassicolens (Cabbage Parachute) as belonging to rotting cabbage, and it has two close relatives that smell even more offensive. This modestly sized, pale-brownish toadstool with a dark, minutely bristly stipe is found in woodland litter, and its nasty and peculiar smell is welcome to the forayer as a way of distinguishing it from several similar species that only smell of garlic! Fungi are chemical magicians, and most of those chemicals are complex organic molecules exhibiting the endless versatility of carbon to make friends with oxygen, hydrogen and nitrogen. There are a few smells that seem to be simpler – more inorganic chemistry than organic. A tiny amount of cyanide – no more than that in a bay leaf – can be picked up from the common and perfectly edible Fairy Ring Mushroom if the fruit bodies are put in a tin for half an hour before sniffing. An unpleasant smell of gas emanates from the gills of the common discovery Stinking Dapperling, Lepiota cristata, which looks like a very diminutive copy of the pleasant-smelling Parasol Mushroom. Among the bonnets there are species that smell of chlorine or nitric acid. One of these is a small, trooping greyish toadstool with a conical cap (M. leptocephala) that often comes up in great numbers in coniferous woods: when crushed, its flesh exudes a strong smell of bleach. Nobody is tempted to ask: ‘Can you eat it?’
So far as I know, people have not succeeded in making perfume out of fungi, although one company in Boston seems to be trying. By contrast, flowering plants are synonymous with pleasant aromas – roses, lavender, gardenia, jasmine and so on – which form the basis of the vast fragrance industry. Even the most fervent Italian enthusiast for porcini might draw the line at finding their lover doused in essence of Boletus edulis. Nonetheless, a handful of fungi do have sweetish smells. A common relative of the Sulphur Knight with similar stature, but having an unremarkable green-tinted, greyish cap colour and white gills, is rather disparagingly known as the Soapy Knight (Tricholoma saponaceum). It has a pleasant, if slightly sickly-sweet aroma. In the nineteenth century it was originally described as smelling ‘like harlots’. Presumably the author, Elias Magnus Fries, considered that his fellow mycologists would readily recognise the comparison. Modern books tactfully refer to ‘cheap soap’.
Some fungi smell of honey. I knew something was going wrong when I could not detect the sweet smell of a pretty red waxcap mushroom called Hygrocybe reidii. The textbooks gave ‘odour of honey’ as an important discriminatory feature of the species to separate it from many other kinds of small, red waxcaps growing in nutrient-poor grasslands. I could not smell a thing. This olfactory failure was the beginning of a slow decline. Over the last decade I have been progressively losing my sense of smell. Sweet smells were lost first, and then one by one others faded away. It was not just mushrooms – no more roses for me, nor savouring the subtle notes of white wine. No more summer evenings enjoying the honeysuckle. I could not even detect the wholesome aroma of a fresh Field Mushroom. Some of the fibrecaps (Inocybe) smell of ripe pears, and I could no longer discriminate those from similar-looking species that had a spermatic (semen) odour. For a while I could still pick up the famous ‘new meal’ smell of St George’s Mushroom, and the strong aniseed fragrance of Clitocybe odora and the young Horse Mushroom (Agaricus arvensis) cut through the decline in my nasal function, but I had to face up to the fact that I was losing one of the most important senses to have in the field. I was no longer master of my own nose. The condition is called anosmia, which is rather like describing losing a leg as ‘apodia’. It does not help much. It is apparently not uncommon in the senior years, and I remembered that my mother had suffered the same loss before she died.
Nonetheless, something had to be done. Nowadays, on a teaching foray the first thing I do is ask among the group who has a well-developed sense of smell and appoint them as the ‘Official Nose’. Those in possession of a distinguished-looking anterior appendage tend to get first look, though I soon learned that good sniffers don’t necessarily have huge noses. Young females are often the most sensitive. I pass the first fruit body to the Official Nose and ask him/her to confirm (or not) that the specimen in question smells of potatoes/bitter almonds/old socks. The specimen then continues its journey round the other noses to have its aromatic volatiles sampled by the assembled nostrils. Usually, this works very well, though I once chose a Nose who obviously enjoyed disagreeing with the accepted word on pongs. If I said sotto voce that this small mushroom smells of radishes it would be countered by ‘No, I think it is more like kohlrabi.’ ‘Camembert cheese?’ ‘No, much more like Epoisses, in my opinion.’ Then it was a relief to discover the Sulphur Knight with its uncontroversial, if penetrating hum to restore faith in the leadership.