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Boletus edulis (English: cep, penny bun, porcino) is a basidiomycete fungus, and the type species of the genus Boletus. It is prized as an edible mushroom.
The fungus produces Basidiospore-bearing basidiocarp above ground in summer and autumn. The fruit body has a large brown cap which on occasion can reach , rarely in diameter and in weight. Like other , it has tubes extending downward from the underside of the cap, rather than gills; spores escape at maturity through the tube openings, or pores. The pore surface of the B. edulis fruit body is whitish when young, but ages to a greenish-yellow. The stout stipe, or stem, is white or yellowish in colour, up to , rarely tall and thick, and partially covered with a raised network pattern, or .
The fungus grows in deciduous forest and forests and tree , forming symbiotic associations with living trees by enveloping the tree's underground roots with sheaths of fungal tissue. Widely distributed in the Northern Hemisphere across Eurasia and North America, it does not occur naturally in the Southern Hemisphere, although it has been introduced to southern Africa, Australia, New Zealand, and Brazil. Several closely related European mushrooms formerly thought to be varieties or forms of B. edulis have been shown using molecular phylogenetic analysis to be distinct species, and others previously classed as separate species are with this species. The western North American species commonly known as the California king bolete ( Boletus edulis var. grandedulis) is a large, darker-coloured variant first formally identified in 2007.
B. edulis is held in high regard in many cuisines, and is commonly prepared and eaten in soups, pasta, or risotto. The mushroom is low in fat and digestible , and high in protein, , dietary mineral and dietary fibre. Although it is sold commercially, it is very difficult to fungiculture. Available fresh in autumn throughout Europe and Russia, it is most often dried, packaged, and distributed worldwide. It keeps its flavour after drying, and it is then reconstituted and used in cooking. B. edulis is also one of the few fungi sold pickled.
Boletus edulis is the type species of the genus Boletus. In Rolf Singer's classification of the Agaricales mushrooms, it is also the type species of section Boletus, a grouping of about 30 related boletes united by several characteristics: a mild-tasting, white flesh that does not change colour when exposed to air; a smooth to distinctly raised, netted pattern over at least the uppermost portion of the stem; a yellow-brown or olive-brown spore print; white tubes that later become yellowish then greenish, which initially appear to be stuffed with cotton; and cystidia that are not strongly coloured. Molecular analysis published in 1997 established that the bolete mushrooms are all monophyly, and established the Boletales as an order separate from the Agaricales.
The genus name is derived from the Latin term bōlētus "mushroom", which was borrowed in turn from the Ancient Greek βωλίτης, "terrestrial fungus". Ultimately, this last word derives from bōlos/βῶλος "lump", "clod", and, metaphorically, "mushroom". The βωλίτης of Galen, like the boletus of Latin writers like Martial, Seneca and Petronius,Peter Howell, A Commentary on Book One of the Epigrams of Martial, The Athlone Press, 1980 p.152-3. Howell doubts the identification, and mentions the view advanced by Augusta A. Imholtz Jr., 'Fungi and piace- names, thè origin of boletus,' in AJP Vol.98, 1977 pp.71f., that the Latin word may derive from the Spanish town Boletum, modern-day Boltaña, south of the Pyrenees, which is still famous for its mushrooms. is often identified as the much prized Amanita caesarea. The specific epithet edulis in Latin means "eatable" or "edible".
Boletus edulis is considered one of the safest wild mushrooms to pick for the table, as few poisonous species closely resemble it, and those that do may be easily distinguished by careful examination. The most similar poisonous mushroom may be the devil's bolete ( Rubroboletus satanas), which has a similar shape, but has a red stem and stains blue on bruising. It is often confused with the very bitter and unpalatable Tylopilus felleus, but can be distinguished by the reticulation on the stalk; in porcini, it is a whitish, net-like pattern on a brownish stalk, whereas it is a dark pattern on white in the latter. Porcini have whitish pores while the other has pink. If in doubt, tasting a tiny bit of flesh will yield a bitter taste. It can also resemble the "bolete-like" Gyroporus castaneus, which is generally smaller, and has a browner stem. Boletus huronensis, an uncommon mushroom of northeastern North America, is another recognized look-alike known to cause severe gastrointestinal disorders.
The spores are elliptical to spindle-shaped, with dimensions of 12–17 by 5–7 μm. The basidia, the spore-bearing cells, are produced in a layer lining the tubes, and arrange themselves so their ends are facing the center of the tube; this layer of cells is known technically as a hymenium. The basidia are thin-walled, mostly attached to four spores, and measure 25–30 by 8–10 μm. Another cell type present in the hymenium is the cystidia, larger sterile cells that protrude beyond the basidia into the lumen of the hymenium, and act as air traps, regulating humidity.
Molecular phylogenetic analyses have proven these three are all distinctive and separate species; other taxa formerly believed to be unique species or subspecies, such as B. betulicola, B. chippewaensis, B. persoonii, B. quercicola and B. venturii, are now known to be part of a B. edulis species complex with a wide morphological, ecological and geographic range, and that the genetic variability in this complex is low. Similar molecular technology has been developed to rapidly and accurately identify B. edulis and other commercially important fungi.
Three divergent lineages found in Yunnan province in China that are commonly marketed and sold as B. edulis (and are actually more closely related to B. aereus) were described in 2013 as B. bainiugan, B. meiweiniuganjun and Boletus shiyong. The classification has since been updated and expanded. All lineages are still members of Boletus sect. Boletus, the sensu sticto "porcini clade" of the genus.
Western North America has several species closely related to B. edulis. The white king bolete ( B. barrowsii), found in parts of Colorado, New Mexico, Arizona, and California (and possibly elsewhere), is named after its discoverer Chuck Barrows. It is lighter in colour than B. edulis, having a cream-coloured cap with pink tones;
Boletus edulis has a cosmopolitan distribution, concentrated in cool-temperate to subtropical regions. It is common in Europe—from northern Scandinavia, south to the extremities of Greece and Italy—and North America, where its southern range extends as far south as Mexico. It is well known from the Borgotaro area of Parma, Italy, and has PGI status there. The European distribution extends north to Scandinavia and south to southern Italy and Morocco. In North America, it can be found from May to October inland and August to January on the West Coast. In China, the mushroom can be found from the northeastern Heilongjiang to the Yunnan–Guizhou Plateau and Tibet. It has been recorded growing under Pinus and Tsuga in Sagarmatha National Park in Nepal, as well as in the Indian forests of Arunachal Pradesh. In West Asia, the species has been reported from the northwest forests of Iran.
The mushroom has been noted to often co-occur with Amanita muscaria or A. rubescens, although it is unclear whether this is due to a biological association between the species, or because of similarities in growing season, habitat, and ecological requirements. An association has also been reported between B. edulis and Amanita excelsa on Pinus radiata ectomycorrhizae in New Zealand, suggesting that other fungi may influence the life cycle of porcini. A 2007 field study revealed little correlation between the abundance of fruit bodies and presence of its mycelia below ground, even when soil samples were taken from directly beneath the mushroom; the study concluded that the triggers leading to formation of mycorrhizae and production of the fruit bodies were more complex.
Boletus edulis is a food source for animals such as the banana slug (Ariolimax columbianus), the long-haired grass mouse, the red squirrel, and, as noted in one isolated report, the fox sparrow.
The flavour of porcini has been described as nutty and slightly meaty, with a smooth, creamy texture, and a distinctive aroma reminiscent of sourdough. Young, small porcini are most appreciated, as the large ones often harbour (insect larvae), and become slimy, soft and less tasty with age. The fruit bodies are collected by holding the stipe near the base and twisting gently. Cutting the stipe with a knife may risk the part left behind rotting and the mycelium being destroyed. Peeling and washing are not recommended. The fruit bodies are highly decomposition, due largely to the high water content (around 90%), the high level of enzyme activity, and the presence of a flora of microorganisms. Caution should be exercised when collecting specimens from potentially polluted or contaminated sites, as several studies have shown that the fruit bodies can bioaccumulation toxic heavy metals like mercury, cadmium, caesium and polonium. Bioaccumulated metals or radionuclide are like chemical signatures: chemical and radiochemistry analysis can be used to identify the origin of imported specimens, and for long-term radioecology monitoring of polluted areas.
Porcini are sold fresh in markets in summer and autumn in Europe and Russia, and dried or canned at other times of the year, and distributed worldwide to countries where they are not otherwise found.
Like other boletes, porcini can be dried by being strung separately on twine and hung close to the ceiling of a kitchen. Alternatively, the mushrooms can be dried by cleaning with a brush (washing is not recommended), and then placing them in a wicker basket or bamboo steamer on top of a boiler or hot water tank.Carluccio, p. 97. Another method is drying in an oven at for two to three hours, then increasing the temperature to until crisp or brittle. Once dry, they must be kept in an airtight container. Importantly for commercial production, porcini retain their flavour after industrial preparation in a pressure cooker or after canning or bottling, and are thus useful for manufacturers of soups or stews. The addition of a few pieces of dried porcino can significantly add to flavour, and they are a major ingredient of the pasta sauce known as carrettiera (carter's sauce). The drying process is known to induce the formation of various volatile substances that contribute to the mushroom's aroma. Chemical analysis has shown that the odour of the dried mushroom is a complex mixture of 53 volatile compounds.
In the vicinity of Borgotaro in the Province of Parma of northern Italy, the four species Boletus edulis, B. aereus, B. aestivalis and B. pinophilus have been recognised for their superior taste and officially termed Fungo di Borgotaro. Here these mushrooms have been collected for centuries and exported commercially. Owing to the globalisation of the mushroom trade most of the porcini commercially available in Italy or exported by Italy no longer originate there. Porcini and other mushrooms are also imported into Italy from various locations, especially China and eastern European countries; these are then often re-exported under the "Italian porcini" label.
In Italy the disconnect with local production has had an adverse effect on quality; for example in the 1990s some of the dried porcino mushrooms exported to Italy from China contained species of genus Tylopilus, which are rather similar in appearance and when dried are difficult for both mushroom labourers and mycologists alike to distinguish from Boletus. Tylopilus species typically have a very bitter taste, which is imparted to the flavour of the porcini with which they are mixed.
After the fall of the Iron Curtain and the subsequent reduction of economic and political barriers, central and eastern European countries with local mushroom harvesting traditions, such as Albania, Bulgaria, Macedonia, Romania, Serbia and Slovenia, developed into exporters of porcini, concentrating primarily on the Italian market. Porcini and other wild fungi from these countries are also destined for France, Germany and other western European markets, where demand for them exists but collection on a commercial scale does not. Picking B. edulis has become an annual seasonal income earner and pastime in countries like Bulgaria, especially for many Romani people communities and the unemployment. A lack of control of the harvest has led to heavy exploitation of the mushroom resource.
Like many other strictly mycorrhizal fungi, B. edulis has eluded cultivation attempts for years. The results of some studies suggest that unknown components of the soil microflora might be required for B. edulis to establish a mycorrhizal relationship with the host plant.
The total lipid, or crude fat, content makes up 3% of the dry matter of the mushroom. The proportion of (expressed as a % of total fatty acids) are: linoleic acid 42%, oleic acid 36%, palmitic acid 10%, and stearic acid 3%.
A comparative study of the amino acid composition of eleven Portuguese wild edible mushroom species showed Boletus edulis to have the highest total amino acid content.
B. edulis mushrooms are rich in the dietary minerals, sodium, iron, calcium, and magnesium, with amounts varying according to the mushroom component and to soil composition in the geographic region of China where they were sampled. They also have high content of B vitamins and . B. edulis contains appreciable amounts of selenium, a trace mineral, although the bioavailability of mushroom-derived selenium is low.
Footnotes
Citations
(1996). 9780471522294, John Wiley and Sons. ISBN 9780471522294 B. edulis has pleurocystidia (cystidia located on the face of a pore) that are thin-walled, roughly spindle-shaped to ventricose, and measure 30–45 by 7–10 μm; the "stuffed" feature of the hymenium is caused by cheilocystidia—cells found on the edges of the pores. (1976). 9783768210621, J. Cramer. ISBN 9783768210621 The of B. edulis do not have .
Related species
Several similar brownish-coloured species are sometimes considered subspecies or forms of this mushroom. In Europe, in addition to B. edulis (or cèpe de Bordeaux), the most popular are:
(2025). 9780762731091, Falcon Guide. ISBN 9780762731091 often with Ponderosa pine, it tends to grow in areas where there is less rainfall. Some find its flavour as good as if not better than B. edulis. The California king bolete ( Boletus edulis var. grandedulis) can reach massive proportions, and is distinguished from B. edulis by a mature pore surface that is brown to slightly reddish. The cap colour appears to be affected by the amount of light received during its development, and may range from white in young specimens grown under thick forest canopy, to dark-brown, red-brown or yellow brown in those specimens receiving more light. The queen bolete ( Boletus regineus), formerly considered a variety of B. aereus, is also a choice edible. It is generally smaller than B. edulis, and unlike that species, is typically found in . The spring king bolete ( Boletus rex-veris), formerly considered a variety of B. edulis or B. pinophilus, is found throughout western North America. In contrast to B. edulis, B. rex-veris tends to fruit in clusters, and, as its common name suggests, appears in the spring. B. fibrillosus is edible but considered inferior in taste.
Habitat and distribution
The fruit bodies of Boletus edulis can grow singly or in small clusters of two or three specimens. The mushroom's habitat consists of areas dominated by pine ( Pinus spp.), spruce ( Picea spp.), hemlock ( Tsuga spp.) and fir ( Abies spp.) trees, although other hosts include chestnut, Chrysolepis, beech, Keteleeria spp., Lithocarpus spp., and oak. In California, porcini have been collected in a variety of forests, such as coastal forests, dry interior oak forests and and interior high-elevation Montane forest , to an altitude of . In northwestern Spain, they are common in dominated by the Cistaceae species Cistus ladanifer and Halimium lasianthum. In Southern France, they are especially favoured and locally called cèpe de Bordeaux after the town from which they are traded to the north and abroad.
Cultivation
Some steps have been made towards cultivating Boletus edulis, including mycorrhization of Cistus ladanifer shrubs enhanced by helper bacteria.
Non-native introductions
Boletus edulis grows in some areas where it is not believed to be indigenous. It is often found underneath oak and Betula pendula in Hagley Park in central Christchurch, New Zealand, where it is likely to have been introduced, probably on the roots of container-grown beech, birch, and oak in the mid-19th century—around the time exotic trees began to be planted in the Christchurch area. Similarly, it has been collected in Adelaide Hills region of Australia in association with three species of introduced trees. It has been growing plentifully in association with pine forests in the southern KwaZulu-Natal Midlands in South Africa for more than 50 years and is believed to have been introduced with the import of pine trees. It also grows in pine plantations in neighboring Zimbabwe.
Ecology
Fruit body production
Italian folklore holds that porcini sprout up at the time of the new moon; research studies have tried to investigate more scientifically the factors that influence the production of fruit bodies. Although fruit bodies may appear any time from summer to autumn (June to November in the UK), their growth is known to be triggered by rainfall during warm periods of weather followed by frequent autumn rain with a drop in soil temperature. Above average rainfall may result in the rapid appearance of large numbers of boletes, in what is known in some circles as a "bolete year". (1977). 9780140630053, Penguin. ISBN 9780140630053 A 2004 field study indicated that fruit body production is enhanced by an open and sunny wood habitat, corroborating an earlier observation made in a Zimbabwean study; removal of the litter layer on the forest floor appeared to have a negative effect on fruit body production, but previous studies reported contradictory results. A Lithuanian study conducted in 2001 concluded that the maximal daily growth rate of the cap (about 21 mm or 0.8 in) occurred when the relative air humidity was the greatest, and the fruit bodies ceased growing when the air humidity dropped below 40%. Factors most likely to inhibit the appearance of fruit bodies included prolonged drought, inadequate air and soil humidity, sudden decreases of night air temperatures, and the appearance of the first frost. Plots facing north tend to produce more mushrooms compared to equivalent plots facing south.
Mycorrhizal associations
Boletus edulis is —it is in a mutualistic relationship with the roots of plants (hosts), in which the fungus exchanges nitrogen and other nutrients extracted from the environment for carbon fixation from the host. Other benefits for the plant are evident: in the case of the Chinese chestnut, the formation of mycorrhizae with B. edulis increases the ability of plant seedlings to resist moisture stress, and increases leaf succulent plants, leaf area, and water-holding ability. The fungus forms a sheath of tissue around terminal, nutrient-absorbing root tips, often inducing a high degree of branching in the tips of the host, and penetrating into the root tissue, forming, to some mycologists, the defining feature of ectomycorrhizal relationships, a hartig net.Smith, Sally; Read, David. Mycorrhizal Symbiosis. Academic press, 1996 The ectomycorrhizal fungi are then able to exchange nutrients with the plant, effectively expanding the root system of the host plant to the furthest reaches of the symbiont fungi. Compatible hosts may belong to multiple families of that are widely distributed throughout the Northern Hemisphere; according to one 1995 estimate, there are at least 30 host plant species distributed over more than 15 genera. Examples of mycorrhizal associates include Pinus massoniana, Pinus patula, Scots pine, Picea abies, Coast Douglas-fir, Pinus mugo, and Pinus virginiana. The fungus has also been shown to associate with Cistus ladanifer, a pioneer species early stage shrub that is adapted for growth in degraded areas, such as burned forests. These and other Cistus species are ecologically important as fungal reservoirs, maintaining an inoculum of mycorrhizal fungi for trees that appear later in the forest regrowth cycle.
Heavy-metal contamination
Boletus edulis is known to be able to tolerate and even thrive on soil that is contaminated with toxic heavy metals, such as soil that might be found near metal smelters. The mushroom's resistance to heavy-metal toxicity is conferred by a biochemical called a phytochelatin—an oligopeptide whose production is induced after exposure to metal. Phytochelatins are chelating agents, capable of forming multiple bonds with the metal; in this state, the metal cannot normally react with other elements or ions and is stored in a detoxified form in the mushroom tissue.
Pests and predators
The fruit bodies of B. edulis can be infected by the parasitic mould-like fungus Hypomyces chrysospermus, known as the bolete eater, which manifests itself as a white, yellow, or reddish-brown cottony layer over the surface of the mushroom. Some reported cases of Abdominal pain following consumption of dried porcini have been attributed to the presence of this mould on the fruit bodies. The mushroom is also used as a food source by several species of mushroom flies, as well as other insects and their . An unidentified species of virus was reported to have infected specimens found in the Netherlands and in Italy; fruit bodies affected by the virus had relatively thick stems and small or no caps, leading to the name "little-cap disease".
Culinary uses
Boletus edulis, as the species epithet edulis () indicates, is an edible mushroom. Italian chef and restaurateur Antonio Carluccio described it as representing "the wild mushroom par excellence", and hailed it as the most rewarding of all fungi in the kitchen for its taste and versatility. Considered a choice edible, particularly in France, Germany, Poland and Italy, it was widely written about by the Roman writers Pliny the Elder and Martial, although ranked below the esteemed Amanita caesarea. When he was served suilli instead of boleti, (1998). 9780801857409, The Johns Hopkins University Press. ISBN 9780801857409 the disgruntled Martial wrote:
(2025). 9783833112393, Könemann. ISBN 9783833112393 They are eaten and enjoyed raw, sautéed with butter, ground into pasta, in soups, and in many other dishes. In France, they are used in recipes such as cèpes à la Bordelaise, cèpe frits and cèpe aux tomates. Porcini risotto is a traditional Italian autumn dish.Carluccio, p. 166. Porcini are a feature of many cuisines, including Provence, and Vienna. In Thailand they are used in soups and consumed blanched in salads. Porcini can also be frozen, either while raw or after cooking in butter. The colour, aroma, and taste of porcini deteriorate noticeably after being frozen for four months. Blanching (or soaking and blanching) as a processing step before freezing can extend the freezer life to 12 months. They are also one of the few species sold commercially as pickled mushrooms.Carluccio, p. 99.
Dried
Boletus edulis is well suited to drying—its flavour intensifies, it is easily reconstituted, and its resulting texture is pleasant.Carluccio, p. 96. Reconstitution is done by soaking in hot, but not boiling, water for about twenty minutes; the water used is infused with the mushroom aroma and it too can be used in subsequent cooking. Dried porcini have more protein than most other commonly consumed vegetables, apart from . Some of their protein is indigestible, though digestibility is improved with cooking.
Commercial harvest
A 1998 estimate suggested that the total annual worldwide consumption of Boletus edulis and closely related species ( B. aereus, B. pinophilus, and B. reticulatus) was between 20,000 and 100,000 tons. Approximately 2,700 tonnes (3,000 Short ton) were sold in France, Italy and Germany in 1988, according to official figures. The true amount consumed far exceeds this, as the official sales figures did not account for informal sales or consumption by collectors. They are widely exported and sold in dried form, reaching countries where they do not occur naturally, such as Australia and New Zealand. The autonomous community of Castile and León in Spain produces 7,700 tonnes (8,500 tons) annually. In autumn, the price of porcini in the Northern Hemisphere typically ranges between $20 and $80 per kilogram, although in New York in 1997 the wholesale price rose to more than $200 per kilogram due to scarcity.
(1994). 9780792327004, Kluwer Academic Publishers. ISBN 9780792327004 Successful attempts at cultivating B. edulis have been made by Spanish scientists by mycorrhization of Cistus species, with Pseudomonas fluorescens bacteria helping the mycorrhiza.
Nutrition
Boletus edulis mushrooms are 9% , 3% fat, and 7% protein (table). Fresh mushrooms consist of over 80% moisture, although reported values tend to differ somewhat as moisture content can be affected by environmental temperature and relative humidity during growth and storage. (1978). 9780121680503, Academic Press. ISBN 9780121680503 The carbohydrate component contains the glucose, mannitol and α,α-trehalose, the polysaccharide glycogen, and the water-insoluble structural polysaccharide chitin, which accounts for up to 80–90% of dry matter in mushroom . Chitin, hemicellulose, and pectin-like carbohydrates—all indigestible by humans—contribute to the high proportion of insoluble fibre in B. edulis.
Phytochemicals and research
Boletus edulis fruit bodies contain diverse , including 500 mg of ergosterol per 100 g of dried mushroom, and ergothioneine. The fruit bodies contain numerous , especially a high content of rosmarinic acid, and (such as oxalic acid, citric acid, malic acid, succinic acid and ), and .
Aroma
Odor compounds giving B. edulis mushrooms their characteristic fragrance include some 100 components, such as and . In a study of aroma compounds, 1-octen-3-one was the most prevalent chemical detected in raw mushrooms, with having increased aroma effect and elevated content after drying.
In human culture
In 2023, with the signing of bill H.B. 92, Boletus edulis became the state mushroom of Utah.
See also
Cited texts
Categories: Featured Article, Edulis, Fungi Described In 1782, Fungi Of Africa, Fungi Of Asia, Fungi Of Europe, Fungi Of New Zealand, Fungi Of North America, Edible Fungi, Italian Products With Protected Designation Of Origin, Fungi Of Western Asia, Taxa Named By Jean Baptiste François Pierre Bulliard, Fungus Species, Fungi Used For Fiber Dyes
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