By Tjakko Stijve, Daniel Andrey and Walter Goessler
Is it a Pholiota or a Lepiota? Is it edible or poisonous? This beautiful and almost golden luminous mushroom is easily recognisable, but rare. Many mushroom aficionados on both sides of the Atlantic have never seen it. As a result, this rare species had a place of honour at the Mushroom Exhibition 2000, organised by the Société Mycologique de la Riviera, in the town of Vevey, situated on the shores of Lake Geneva in Switzerland.
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The colour of both stipe and pileus was golden brown to orange-tan. The flesh was yellowish. The gills were attached and orange-brownish in colour. The spore print was pale yellow-brown. The mushroom's strong odour was reminiscent of bitter almonds and the taste was mild.
The mushroom was found along a road, at a site called Les Paccots, in the Canton of Fribourg, where it grew in a large fairy ring amidst nettles. Several mycologists and experienced amateurs readily admitted that they had never seen this Phaeolepiota.
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In 45 years of mycological activity we had ourselves seen it only once in The Netherlands, in 1975, where we discovered it near the City of Utrecht, on the slope of a dike, amidst nettles under elder shrubs. At that time identification was not easy, because this spectacular mushroom was not mentioned in the available Dutch and German field guides. However, upon consulting the Dutch adaptation of Morton Lange's Illustreret Svampeflora, we found a description and an illustration that matched. Our find was Phaeolepiota aurea, a rare species, related to Cystoderma, but having ochre-coloured spores.
Confronted for the second time in our life with this remarkable mushroom, we decided to do a literature search to learn more about it. First we checked with what frequency the species was mentioned in field guides, textbooks and encyclopaedia on mushrooms edited between 1860 and 2000. We confined ourselves to the more important volumes, excluding booklets having a too-narrow scope such as "The best edible mushrooms", "Petit Atlas des Champignons", etc. We found that Phaeolepiota aurea was described, and sometimes illustrated, in 30 out of 80 books consulted.
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The species was often absent from German, Swiss, Austrian and English literature, but it was invariably mentioned in Canadian and American field guides. A check of the oldest books revealed consistent confusion between P. aurea and Gymnopilus spectabilis, a large and similarly coloured species that is distinguished from Phaeolepiota by growing in large clumps on stumps of deciduous trees and by its pronounced bitter taste.
For example, in Flore des champignons supérieurs de France (1909), Bigeard and Guillemin described Pholiota aurea as "growing in clusters at the base of trees in sandy soils." The same error was made by Costatin and Dufour in La nouvelle flore des champignons (1912); they also reported a very bitter taste. In a recent article the French mycologist Régis Courtecuisse called the mushroom "la lépiote des Pyrenées," a name that had not been used since 1887, when Quélet described it as Lepiota pyrenaea. The Dutch call it "Goudparasol" (Golden Lepiota), the Japanese "Koganetake", the Germans "Glimmerschüppling", and some American authors have labeled it "Alaskan gold," because it is more often found in that state than elsewhere in the U.S. The mushroom is rare both on the European continent and in the U.K. Erna Bachís monograph on the species (1956) reports only two collections for England and three for Ireland. However, in recent years it has been reported more frequently, notably in Liverpool, and a splendid photograph of the species once graced the cover of The Mycologist. A search on the Internet revealed that Phaeolepiota aurea was mentioned 44 times.
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This extraordinary mushroom looked like a giant Cystoderma amianthinum and most of the visitors to the exhibition had never seen it before. They were surprised to learn that it was the Pholiote Dorée, the French common name for Phaeolepiota aurea (Matt.: Fr.) Maire, also known as Cystoderma aureum Kühn. & Romagn.
European mycologists have continued to disagree on the taxonomic position of this mushroom. It was first described in 1779 as Agaricus aureus by the Czech author Mattuschka. Elias Fries placed it later in the genus Pholiota because of its ochre-coloured spore print. Quélet considered it to be a Lepiota, while Maire transferred it to a new genus, Phaeolepiota. More recently, Kühner and Romagnesi considered the species an oversized representative of Cystoderma, and stated that Phaeolepiota Maire was only acceptable as a subgenus.
The study of chemical characteristics has been most valuable in systematic mycology. For example, many mushrooms produce urea, a nitrogen waste product, at concentrations that increase with the age of the fruitbodies. This feature may be used to delimit a genus, (e.g. Panaeolus species produce ample quantities of this metabolite) from the members of another genus (e.g. Psathyrella).
| Certain subsections within a genus can also be characterised by the presence of urea. A good example is sub-section Volvocoprinus of Coprinus, in which only the ringed Shaggy Mane (C. comatus) and C. sterquilinus produce urea. Molecular systematics based on DNA sequencing has revealed that these taxa are in fact far closer to Agaricus, in which all members of the genus produce urea! Similarly, the development of gaseous hydrogen cyanide seems to be characteristic for certain genera in the Tricholomataceae, although a number of polypores also produce this toxic gas. |
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Chemical Features |
Genus Pholiota (8 species) |
Phaeolepiota aurea (3 collections) |
Lepiota & Macrolepiota (10 species) |
Cystoderma (3 species) |
| Synthesis of urea | nil | Intense | Intense | Intense | ||
| Production of Hydrocyanic acid (HCN) | nil | Intense | nil | nil | ||
| Radiocaesium uptake | weak | nil | nil | nil | ||
| Zinc | 34-54 (44) | 63-121 (90) | 55-176 (114) | 62-87 (69) | ||
| Copper | 30-65 (42) | 47-80 (69) | 21-191 (116) | 38-89 (62) | ||
| Silver | 0.30-0.64 (0.44) | 1.35-2.38 (1.79) | 0.67-28.0 (3.54) | 0.89-11.0 (4.06) | ||
| Mercury | 0.12-0.70 (0.39) | 4.1-30.0 (18.1) | 1.28-7.2 (3.45) | 2.9-24.5 (14.8) | ||
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All values in mg/kg dry weight. Average values are in parentheses. This table compares chemical characteristics of Pholiota spp., Phaeolepiota aurea, and some representatives of Lepiota, Macrolepiota and Cystoderma. Based on these data, it is clear that Phaeolepiota is rather close to Cystoderma. These results, especially the high cadmium concentrations in both Phaeolepiota and Cystoderma, support Kühner and Romagnesi's taxonomic point of view. Nevertheless, HCN production makes Phaeolepiota special. |
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Mushrooms also differ in their capacity to take up certain metals from their substrate. For example, the Blue-Green Anise Mushroom, Clitocybe odora, accumulates copper, whereas Gomphidius species do not take up this metal. In the genus Agaricus, there are many species which accumulate mercury and cadmium. Since the Chernobyl nuclear accident it has been shown that mushrooms also differ tremendously in their affinity for radioactive cesium isotopes.
In some French and Swiss handbooks, Phaeolepiota is presented as a good and even excellent edible. On the other hand, American and Canadian guides are more cautious since it has been reported to cause gastric trouble in some people. Since the 1960s, annual reports from the North American Mycological Association regularly mention cases of mild poisoning (vomiting and diarrhea) caused by this mushroom. However, when consulting classic and modern manuals on mushroom poisoning, one discovers that Phaeolepiota aurea is never mentioned. Perhaps the species is too rare, at least in Europe, to show up in the statistics!
The Belgian mycologist Paul Heinemann discovered in 1942 that the mushroom contains hydrocyanic acid (HCN), a metabolite that is encountered in several edible species, e.g. Marasmius oreades, Clitocybe geotropa, Clitocybe gibba and Pseudoclitocybe cyathiformis, etc. Even cultivated mushrooms like the Golden Oyster (Pleurotus citrino-pileatus), P. eryngii and even good old Shiitake (Lentinula edodes) produce measurable quantities of this toxic compound.
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A few years ago, we had the opportunity to study those 150 edible mushrooms which may be sold on the Swiss and German markets. Our results showed that only 14 species, about 9 percent, tested consistently positive for HCN. The amounts produced ranged from 7 to 268 mg/kg. For the three economically most important mushrooms, i.e. the White Button (Agaricus bisporus), the Oyster (Pleurotus ostreatus) and the Paddy Rice Straw Mushroom (Volvariella volvacea), the test was negative. To determine whether HCN constituted a health risk to the consumer, we subjected several mushrooms to various processing and culinary preparation procedures. Invariably, the toxic compound had disappeared entirely by the time the dish was prepared.
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At the end of the afore-mentioned mycological exhibition we obtained five specimens of Phaeolepiota aurea to study its chemical constituents, including HCN. We were surprised to discover that it contained 510 mg/kg of HCN, a concentration twice as high as that reported for Marasmius oreades, which is generally thought to be the cyanogenic mushroom "par excellence." After preparing Phaeolepiota according to a recipe given for Macrolepiota procera (the Parasol mushroom), we found that the dish still contained about 200 mg/kg, which contradicts the generally accepted idea that heat readily volatilises the toxicant. Of course, we are aware that HCN does not occur as such in the mushroom, but as a precursor, from which it is only slowly released.
Japanese researchers have reported similar observations for Tricholoma giganteum, a rather common species in Japan and Australia. In their experiments, the residual HCN content was also found to be appreciable. In fact, the authors thought it might be high enough to provoke a mild poisoning syndrome in sensitive people. Perhaps this explains why Phaeolepiota has occasionally caused discomfort upon consumption. Finally, we have seen that P. aurea also takes up heavy metals, notably the very toxic cadmium. Analysis of our collections revealed appreciable concentrations of this metal. Unpublished data communicated by the Italian mycochemist Luigi Cocchi show that it can be as high as 41 mg/kg on dry matter, an amount that readily exceeds the European maximum limit for cultivated mushrooms! We should therefore just admire this beautiful mushroom and abstain from eating it.
E. Bach, 1956. "The Agaric Pholiota aurea - Physiology and Ecology." Dansk Botanisk Archiv 16(2): 1-220.
T. Stijve and A.A.R. de Meijer, 1999. "Hydrocyanic acid in mushrooms, with special reference to wild-growing and cultivated edible species." Deutsche Lebensmittel Rundschau 95: 366-372.
Tatsaya Shindo et al., 1998. "Study on content of cyanide in basidiomycetes and the effect of cooking." Journal of Food Hygienic Society of Japan 40(1):29-33.
This article first appeared in the Fall, 2002 issue of Mushroom, the Journal of Wild Mushrooming.
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