Biology:Boletus edulis

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Short description: Species of mushroom, widely distributed in the Northern Hemisphere

Boletus edulis
Two mushrooms with brown caps and light brown stems growing on the ground, surrounded by fallen leaves and other forest debris. One mushroom has been plucked and lies beside the other; its under-surface is visible, and is a light yellow colour.
In the northern Apennine Mountains, Abetina Reale forest, Italy
Scientific classification edit
Domain: Eukaryota
Kingdom: Fungi
Division: Basidiomycota
Class: Agaricomycetes
Order: Boletales
Family: Boletaceae
Genus: Boletus
Species:
B. edulis
Binomial name
Boletus edulis
Bull. (1782)
Synonyms[2]
  • Ceriomyces crassus Battarra (1775)
  • Boletus solidus Sowerby (1809)
  • Leccinum edule (Bull.) Gray (1821)
  • Dictyopus edulis (Bull.) Forq. (1890)
Boletus edulis
View the Mycomorphbox template that generates the following list
Mycological characteristics
pores on hymenium
cap is convex
hymenium is adnate
stipe is bare
spore print is brown
ecology is mycorrhizal
edibility: choice

Boletus edulis (English: cep, penny bun, porcino or porcini) is a basidiomycete fungus, and the type species of the genus Boletus. Widely distributed in the Northern Hemisphere across Europe, Asia, 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 conspecific 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.

The fungus grows in deciduous and coniferous forests and tree plantations, forming symbiotic ectomycorrhizal associations with living trees by enveloping the tree's underground roots with sheaths of fungal tissue. The fungus produces spore-bearing fruit bodies above ground in summer and autumn. The fruit body has a large brown cap which on occasion can reach 30 cm (12 in), rarely 40 cm (16 in) in diameter and 3 kg (6 lb 10 oz) in weight. Like other boletes, 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 20 cm (8 in), rarely 30 cm (12 in) tall and 10 cm (4 in) thick, and partially covered with a raised network pattern, or reticulations.

Prized as an ingredient in various culinary dishes, B. edulis is an edible mushroom 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 carbohydrates, and high in protein, vitamins, minerals and dietary fibre. Although it is sold commercially, it is very difficult to cultivate. 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 one of the few fungi sold pickled.

Taxonomy

Side view of the head and upper body of a man wearing a dark jacket and white ruffled collar.
Pierre Bulliard first described B. edulis in 1782.

Boletus edulis was first described in 1782 by the French botanist Pierre Bulliard and still bears its original name.[3] The starting date of fungal taxonomy had been set as January 1, 1821, to coincide with the date of the works of the 'father of mycology', Swedish naturalist Elias Magnus Fries, which meant the name required sanction by Fries (indicated in the name by a colon) to be considered valid, as Bulliard's work preceded this date. It was thus written Boletus edulis Bull.:Fr. A 1987 revision of the International Code of Botanical Nomenclature set the starting date at May 1, 1753, the date of publication of Linnaeus' work, the Species Plantarum.[4] Hence, the name no longer requires the ratification of Fries' authority. Early alternate names include Boletus solidus by English naturalist James Sowerby in 1809,[5] and Gray's Leccinum edule.[6] Gray's transfer of the species to Leccinum was later determined to be inconsistent with the rules of botanical nomenclature, and he apparently was unfamiliar with the earlier works of Fries when he published his arrangement of bolete species.[7]

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.[8][9] Molecular analysis published in 1997 established that the bolete mushrooms are all derived from a common ancestor, and established the Boletales as an order separate from the Agaricales.[10]

The generic name is derived from the Latin term bōlētus "mushroom", which was borrowed in turn from the Ancient Greek βωλίτης, "terrestrial fungus".[11] Ultimately, this last word derives from bōlos/βῶλος "lump", "clod", and, metaphorically, "mushroom".[12] The βωλίτης of Galen, like the boletus of Latin writers like Martial, Seneca and Petronius,[13] is often identified as the much prized Amanita caesarea.[14] The specific epithet edulis in Latin means "eatable" or "edible".[15]

Common names

Common names for B. edulis vary by region. The standard Italian name, porcino (pl. porcini), means porcine;[16] fungo porcino, in Italian, echoes the term suilli, literally "hog mushrooms", a term used by the Ancient Romans[17] and still in use in southern Italian terms for this species.[18] The derivation has been ascribed to the resemblance of young fruit bodies to piglets, or to the fondness pigs have for eating them.[19] It is also known as "king bolete".[20] The English penny bun refers to its rounded brownish shape. The German name Steinpilz (stone mushroom) refers to the species' firm flesh.[21] In Austria, it is called Herrenpilz, the "noble mushroom",[19] while in Mexico, the Spanish name is panza, meaning "belly".[22] Another Spanish name, rodellon, means "small round boulder", while the Dutch name eekhoorntjesbrood means "squirrel's bread".[23] Russian names are belyy grib (:ru:белый гриб; "white mushroom" as opposed to less valuable "black mushrooms") and borovik (:ru:боровик; from bor—"pine forest"). The vernacular name cep is derived from the Catalan cep or its French name cèpe, although the latter is a generic term applying to several related species. In France, it is more fully cèpe de Bordeaux, derived from the Gascon cep "trunk" for its fat stalk,[24] ultimately from the Latin cippus "stake".[25] Ceppatello, ceppatello buono, ceppatello bianco, giallo leonato, ghezzo, and moreccio are names from Italian dialects,[26][27] and ciurenys or surenys is another term in Catalan.[28] The French-born King Charles XIV John popularised B. edulis in Sweden after 1818,[29] and is honoured in the local vernacular name Karljohanssvamp, as well as the Danish name Karl Johan svamp. The monarch cultivated the fungus about his residence, Rosersberg Palace.[30] The Finnish name is herkkutatti, from herkku 'delicacy', and tatti, 'bolete'.

Description

Both halves of a thick-stemmed bisected mushroom.
Cross-section showing white flesh, broad stem, and spore tubes on the underside of the cap

The cap of this mushroom is 7–30 cm (3–12 in) broad at maturity. Slightly sticky to touch, it is convex in shape when young and flattens with age. The colour is generally reddish-brown fading to white in areas near the margin, and continues to darken as it matures. The stipe, or stem, is 8–25 cm (3–10 in) in height, and up to 7 cm (3 in) thick—rather large in comparison to the cap;[31] it is club-shaped, or bulges out in the middle. It is finely reticulate on the upper portion, but smooth or irregularly ridged on the lower part. The under surface of the cap is made of thin tubes, the site of spore production; they are 1 to 2 cm (1⁄2 to 3⁄4 in) deep, and whitish in colour when young, but mature to a greenish-yellow.[32] The angular pores, which do not stain when bruised, are small—roughly 2 to 3 pores per millimetre.[33] In youth, the pores are white and appear as if stuffed with cotton (which are actually mycelia); as they age, they change colour to yellow and later to brown. The spore print is olive brown. The flesh of the fruit body is white, thick and firm when young, but becomes somewhat spongy with age. When bruised or cut, it either does not change colour, or turns a very light brown or light red.[34] Fully mature specimens can weigh about 1 kg (2 lb 3 oz); a huge specimen collected on the Isle of Skye, Scotland, in 1995 bore a cap of 42 cm (16 1⁄2 in), with a stipe 18 cm (7 in) in height and 14 cm (5 1⁄2 in) wide, and weighed 3.2 kg (7 lb 1 oz).[31] A similarly sized specimen found in Poland in 2013 made international news.[35]

A brown-capped mushroom lying flat on the grass with a white or light-brown coloured stem that gradually gets thicker, so as to roughly resemble the shape of a club.
A brown-capped mushroom with a short, stout stem that is thickest in the middle, and whose thickness approaches the width of the cap it supports.
Stem shape can range from club-shaped to centrally bulbous

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.[19] 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.[19] 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.[19] 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.[36]

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.[37] 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.[32] The hyphae of B. edulis do not have clamp connections.[33]

Related species

A mushroom with an orange-brown cap and a yellowish underside that somewhat resembles a sponge. The light-yellow stem is about half the thickness of the caps diameter. This mushroom is growing on the ground, surrounded by twigs, leaves, log and other forest floor debris.
B. edulis var. grandedulis
A mushroom with a reddish-brown cap that is curled upwards to reveal a cream-coloured porous underside that somewhat resembles a sponge. The thick stipe has a pinkish hue, and its thickness is a little less than half of the cap's diameter. The mushroom has been pulled from the ground and the end of its stipe is a whitish colour caused by hyphal tufts, and is embedded with dirt and other small twigs.
B. regineus

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:

  • Cèpe bronzé ("dark cep"; Boletus aereus), much rarer than B. edulis, is more highly regarded by gourmets, and consequently more expensive. Usually smaller than B. edulis, it is also distinctively darker in colour.[19] It is especially suited to drying.[20]
  • Cèpe des pins ("pine tree cep"; Boletus pinophilus or Boletus pinicola) grows among pine trees. Rarer than B. edulis, it is less appreciated by gourmets than the two other kinds of porcini, but remains a mushroom rated above most others.[20]
  • Cèpe d'été ("summer cep"; Boletus reticulatus), also less common and found earlier.[19]

Molecular phylogenetic analyses have proven these three are all distinctive and separate species;[38] 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,[39][40] and that the genetic variability in this complex is low.[41] Similar molecular technology has been developed to rapidly and accurately identify B. edulis and other commercially important fungi.[42][43]

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 B. shiyong.[44][45] 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.[46]

A group of three mushrooms with reddish-brown caps, bright yellow porous undersides, and thick white stipes. They are growing on the ground in soil covered with pine needles.
B. rex-veris

Western North America has several species closely related to B. edulis. The white king bolete (Boletus barrowsii), found in parts of Colorado, New Mexico, Arizona, and California (and possibly elsewhere), is named after its discoverer Chuck Barrows.[47] It is lighter in colour than B. edulis, having a cream-coloured cap with pink tones;[48] often mycorrhizal 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.[49] 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 canopy, to dark-brown, red-brown or yellow brown in those specimens receiving more light.[50] 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 mixed forests.[51] 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.[52] B. fibrillosus is edible but considered inferior in taste.[53]

Habitat and distribution

A mushroom with a brown smooth cap the shape of a halved sphere, atop a thick, dirty white stipe. The mushroom is growing on a sloping patch of ground amongst moss, twigs and other forest debris; trees can be faintly seen in the background.
In Lithuania

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, chinquapin, 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 savannas and interior high-elevation montane mixed forests,[54] to an altitude of 3,500 m (11,500 ft).[55] In northwestern Spain, they are common in scrublands dominated by the rock rose species Cistus ladanifer and Halimium lasianthum.[56] In the Midi region of south-west France, they are especially favoured and locally called cèpe de Bordeaux after the town from which they are traded to the north and abroad.[57]

Boletus edulis has a cosmopolitan distribution, concentrated in cool-temperate to subtropical regions.[54] 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.[34] 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.[54] In China, the mushroom can be found from the northeastern Heilongjiang to the Yunnan–Guizhou Plateau and Tibet.[34] It has been recorded growing under Pinus and Tsuga in Sagarmatha National Park in Nepal,[58] as well as in the Indian forests of Arunachal Pradesh.[59] In West Asia, the species has been reported from the northwest forests of Iran.[60]

Cultivation

Some steps have been made towards cultivating Boletus edulis,[61] including mycorrhization of rockrose shrubs enhanced by helper bacteria.[62]

Non-native introductions

Boletus edulis grows in some areas where it is not believed to be indigenous. It is often found underneath oak and silver birch in Hagley Park in central Christchurch, New Zealand, where it is likely to have been introduced,[63] 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.[34] Similarly, it has been collected in Adelaide Hills region of Australia in association with three species of introduced trees.[64] 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.[65][66] It also grows in pine plantations in neighboring Zimbabwe.[67]

Ecology

About half a dozen pine trees with upward-pointing branches 15 to 30 metres in height with green needles. The upper half of the background is blue sky.
B. edulis is ectomycorrhizal and may co-occur with Pinus radiata
A group of three mushrooms, ranging in size from small to large, with red caps dotted with white warts, and white stems. The largest of the three has a droopy skirt hanging from the upper portion of its stem. The mushrooms are growing in the ground, surrounded by fallen brown leaves, green grass, and a dark green bush in the background.
and Amanita muscaria.

Fruit body production

Italian folklore holds that porcini sprout up at the time of the new moon;[19] 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.[54] 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".[68] A 2004 field study indicated that fruit body production is enhanced by an open and sunny wood habitat,[69] corroborating an earlier observation made in a Zimbabwean study;[67] 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.[70][71] 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.[72] Plots facing north tend to produce more mushrooms compared to equivalent plots facing south.[73]

Mycorrhizal associations

Boletus edulis is mycorrhizal—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 fixed carbon 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 water stress, and increases leaf succulence, leaf area, and water-holding ability.[74] 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.[75] 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.[75] Compatible hosts may belong to multiple families of vascular plants 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.[34] Examples of mycorrhizal associates include Chinese red pine,[76] Mexican weeping pine,[77] Scots pine, Norway spruce,[78] Coast Douglas-fir,[79] mountain pine,[80] and Virginia pine.[81] The fungus has also been shown to associate with gum rockrose, a pioneer early stage shrub that is adapted for growth in degraded areas, such as burned forests.[82] These and other rockrose species are ecologically important as fungal reservoirs, maintaining an inoculum of mycorrhizal fungi for trees that appear later in the forest regrowth cycle.[83]

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.[54] 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.[84] 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.[85]

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.[86] 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.[87] Some reported cases of stomach ache following consumption of dried porcini have been attributed to the presence of this mould on the fruit bodies.[88] The mushroom is also used as a food source by several species of mushroom flies,[54] as well as other insects and their larvae.[89] 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".[90][91]

Boletus edulis is a food source for animals such as the banana slug (Ariolimax columbianus),[92] the long-haired grass mouse,[93] the red squirrel,[94] and, as noted in one isolated report, the fox sparrow.[95]

Culinary uses

A porcini mushroom and noodle soup served in a bread bowl at a Polish restaurant
A porcini mushroom sandwich in Stockholm, Sweden

Boletus edulis, as the species epithet edulis (Latin: "edible") directly implies, is an edible mushroom. Italian chef and restaurateur Antonio Carluccio has described it as representing "the wild mushroom par excellence", and hails it as the most rewarding of all fungi in the kitchen for its taste and versatility.[19] Considered a choice edible, particularly in France, Germany, Poland and Italy,[20] it was widely written about by the Roman writers Pliny the Elder and Martial, although ranked below the esteemed Amanita caesarea. When served suilli[lower-alpha 1] instead of boleti,[97] the disgruntled Martial wrote:

sunt tibi boleti; fungos ego sumo suillos (Ep. iii. 60)
("You eat the choice boletus, I have mushrooms that swine grub up.")[98]

The flavour 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 by gourmets, as the large ones often harbour maggots (insect larvae), and become slimy, soft and less tasty with age. 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.[19] The fruit bodies are highly perishable, due largely to the high water content (around 90%), the high level of enzyme activity, and the presence of a flora of microorganisms.[99] Caution should be exercised when collecting specimens from potentially polluted or contaminated sites, as several studies have shown that the fruit bodies can bioaccumulate toxic heavy metals like mercury,[100] cadmium,[101] caesium and polonium.[102][103] Bioaccumulated metals or radioactive fission decay products are like chemical signatures: chemical and radiochemical analysis can be used to identify the origin of imported specimens,[104] and for long-term radioecological monitoring of polluted areas.[105]

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.[106] 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.[107] Porcini risotto is a traditional Italian autumn dish.[108] Porcini are a feature of many cuisines, including Provençal,[109] and Viennese.[110] They are used in soups and consumed blanched in salads in Thailand.[111] Porcini can also be frozen—either raw or first cooked in butter. The colour, aroma, and taste of frozen porcini deteriorate noticeably if frozen longer than four months. Blanching or soaking and blanching as a processing step before freezing can extend the freezer life up to 12 months.[99] They are also one of the few mushroom species pickled and sold commercially.[112]

Dried

A heaped pile of dried sliced mushrooms on a large plate. A sign near the back of the plate reads "Fungo di Borgotaro I.G.P."; another sign at the front reads "Prezzo speciale di Fiera. 3 Etti 18,00". An electronic scale is partially visible on a table behind the mushrooms
A pile of dried porcini at the Borgotaro festival of the porcino, Italy

Boletus edulis is well suited to drying—its flavour intensifies, it is easily reconstituted, and its resulting texture is pleasant.[113] 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 soybeans. Some of this content is indigestible, though digestibility is improved with cooking.[114]

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.[115] Another method is drying in an oven at 25 to 30 °C (77 to 86 °F) for two to three hours, then increasing the temperature to 50 °C (122 °F) until crisp or brittle.[116] Once dry, they are kept in an airtight jar.[115] 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).[117] 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.[118]

Commercial harvest

Approximately two dozen brown-capped, white or light-brown stemmed mushrooms of various sizes in a brown bowl.
Porcini can vary considerably in size.

A 1998 estimate suggests the total annual worldwide consumption of Boletus edulis and closely related species (B. aereus, B. pinophilus, and B. reticulatus) to be between 20,000 and 100,000 tons.[54] Approximately 2,700 tonnes (3,000 tons) were sold in France, Italy and Germany in 1988, according to official figures. The true amount consumed far exceeds this, as it does not account for informal sales or consumption by collectors.[55] 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.[82] 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 scarcity of fruit bodies elevated the wholesale price to more than $200 per kilogram.[55]

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 globalization 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 imported into Italy from various locations, especially China and eastern European countries; these are then often re-exported under the "Italian porcini" label.[119][120]

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.[121]

After the fall of the Iron Curtain and the economic and political barriers that followed, 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.[120] Exported porcini and other wild fungi are also destined for France, Germany and other western European markets, where demand for them exists, but collection on a commercial scale does not.[120] Picking B. edulis has become an annual seasonal income earner and pastime in countries like Bulgaria, especially for many Roma communities and the unemployed.[122] A lack of control has led to heavy exploitation of the mushroom resource.[123]

Like many other strictly mycorrhizal fungi, B. edulis has eluded cultivation attempts for years.[114][124][61] 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.[125][126][127] Successful attempts at cultivating B. edulis have been made by Spanish scientists by mycorrhization of Cistus species,[61] with Pseudomonas fluorescens bacteria helping the mycorrhiza.[62]

Boletus edulis, fresh[128]
Nutritional value per 100 g (3.5 oz)
Energy342.4 kJ (81.8 kcal)
1.70 g
7.39 g
VitaminsQuantity %DV†
Thiamine (B1)
9%
0.105 mg
Riboflavin (B2)
8%
0.092 mg
Niacin (B3)
40%
6.07 mg
Pantothenic acid (B5)
53%
2.64 mg
Vitamin B6
4%
0.051 mg
Folate (B9)
73%
290 μg
Vitamin C
5%
4.21 mg
MineralsQuantity %DV†
Calcium
0%
1.195 mg
Copper
39%
0.786 mg
Iron
6%
0.739 mg
Phosphorus
3%
22.26 mg
Potassium
4%
203.3 mg
Zinc
44%
4.172 mg
†Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database

Nutrition

Boletus edulis mushrooms are 9% carbohydrates, 3% fat, and 7% protein (table). Fresh mushrooms consist of over 80% moisture,[129] although reported values tend to differ somewhat as moisture content can be affected by environmental temperature and relative humidity during growth and storage.[130] The carbohydrate component contains the monosaccharides 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 cell walls. Chitin, hemicellulose, and pectin-like carbohydrates—all indigestible by humans—contribute to high proportion of insoluble fibre in B. edulis.[131]

The total lipid, or crude fat, content makes up 3% of the dry matter of the mushroom. The proportion of fatty acids (expressed as a % of total fatty acids) are: palmitic acid, 10%; stearic acid, 3%; oleic acid, 36%; and linoleic acid, 42%.[132]

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.[133][134]

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.[131][135] They also have high content of B vitamins and tocopherols.[136] B. edulis contains appreciable amounts of selenium, a trace mineral,[137] although the bioavailability of mushroom-derived selenium is low.[138]

Phytochemicals and research

Skeletal formula depicting the amino acids cysteine and glycine joined in a peptide bond, with free carboxy and amino groups at either end of the peptide chain. Parentheses around the peptide bond indicate a variable number of amino acids are involved.
Phytochelatins give B. edulis resistance to toxic heavy metals like cadmium.

Boletus edulis fruit bodies contain diverse phytochemicals, including 500 mg of ergosterol per 100 g of dried mushroom,[139] and ergothioneine.[140] The fruit bodies contain numerous polyphenols, especially a high content of rosmarinic acid,[141] and organic acids (such as oxalic, citric, malic, succinic and fumaric acids),[142] and alkaloids.[143]

Aroma

Aroma compounds giving B. edulis mushrooms their characteristic fragrance include some 100 components, such as esters and fatty acids.[144] In a study of aroma compounds, 1-octen-3-one was the most prevalent chemical detected in raw mushrooms, with pyrazines having increased aroma effect and elevated content after drying.[145]

See also

References

Footnotes

  1. ↑ The term suilli was also thought to encompass the related Leccinum scabrum.[96]

Citations

  1. ↑ Dahlberg, A. (2019). "Boletus edulis (errata version published in 2022)". IUCN Red List of Threatened Species 2019: e.T122090234A222968388. doi:10.2305/IUCN.UK.2019-3.RLTS.T122090234A222968388.en. https://www.iucnredlist.org/species/122090234/222968388. Retrieved 22 January 2024. 
  2. ↑ "Boletus edulis Bull. 1782". MycoBank. International Mycological Association. http://www.mycobank.org/MycoTaxo.aspx?Link=T&Rec=356530. 
  3. ↑ Bulliard JBF. (1782) (in fr). Herbier de la France. Vol 2. Paris, France: P.F. Didot. pp. 49–96, plate 60. https://archive.org/stream/herbierdelafranc4996bull#page/22/mode/2up. Retrieved 2009-11-24. 
  4. ↑ The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research. Heidelberg, Germany: Springer. 1994. p. 81. ISBN 3-540-66493-9. https://archive.org/details/mossflorabritain00libg. 
  5. ↑ Sowerby J. (1809). Coloured Figures of English Fungi. 4. London: J. Davis. p. 199.  This entire work is available in Commons here, but the reference is to plate 419 with textual description on page 697. Sowerby described the same modern species as B. edulis on plate 111 (description on page 57).
  6. ↑ Gray SF. (1821). A Natural Arrangement of British Plants. London: Baldwin, Cradock, and Joy, Paternoster-Row. p. 647. https://books.google.com/books?id=g-EYAAAAYAAJ&q=A%20natural%20arrangement%20of%20British%20plants%20Gray%201821&pg=PA647. Retrieved 2009-11-24. 
  7. ↑ Šutara J. (1985). "Leccinum and the question of superfluous names (Fungi: Boletaceae)". Taxon 34 (4): 678–86. doi:10.2307/1222214. 
  8. ↑ Singer R. (1986). The Agaricales in Modern Taxonomy (4th rev. ed.). Koenigstein, Germany: Koeltz Scientific Books. p. 779. ISBN 3-87429-254-1. 
  9. ↑ The Boletes of Michigan. Ann Arbor, Michigan: University of Michigan Press. 1971. p. 221. http://quod.lib.umich.edu/cgi/t/text/pageviewer-idx?c=fung1tc;cc=fung1tc;idno=agk0838.0001.001;frm=frameset;view=image;seq=229;page=root;size=s. Retrieved 2010-12-02. 
  10. ↑ "Agaricales oder Boletales? Molekularbiologische Befunde zur Zuordnung einiger umstrittener Taxa". Zeitschrift für Mykologie 63: 189–196. 1997. 
  11. ↑ Simpson DP. (1979). Cassell's Latin Dictionary (5 ed.). London: Cassell Ltd. p. 78. ISBN 0-304-52257-0. 
  12. ↑ Liddell HG, Scott R. (1980). A Greek–English Lexicon (Abridged ed.). United Kingdom: Oxford University Press. ISBN 0-19-910207-4. 
  13. ↑ 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.
  14. ↑ Ramsbottom J. (1953). Mushrooms & Toadstools. London, England: Collins. p. 6. ISBN 1-870630-09-2. 
  15. ↑ Latin Dictionary: Morell's Abridgment. London: Moon, Boys & Graves. 1828. pp. 121, 596. https://archive.org/details/bub_gb_U3oTAAAAYAAJ. Retrieved 2009-11-02. 
  16. ↑ "porcino in Vocabolario – Treccani". https://www.treccani.it/vocabolario/porcino. 
  17. ↑ Pliny, Natural History, Bk. 16, 11, 31: "Such is the multiplicity of products in addition to the acorn that are borne by hard-oaks; but they also produce edible fungi (boletos) and hog mushrooms (suillos)." Pliny, Natural History, 10 vols., tr. H. Rackham, Harvard University Press/Heinemann, (1945) 1968, vol. 4, pp. 408–409.
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  21. ↑ Grimm J., Grimm W. (1838–1961). Deutsches Wörterbuch. Leipzig: Hirzel.  (online )
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  25. ↑ "cepe". Oxford English Dictionary (2nd ed.). Oxford: Clarendon Press. 1989. ISBN 0-19-861186-2. 
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  27. ↑ Zeitlmayr L. (1977). I funghi. Edizioni Studio Tesi. p. 180. 
  28. ↑ Andrews, Colman (1999). Catalan cuisine: vivid flavors from Spain's Mediterranean coast (2nd ed.). Boston, MA: Harvard Common Press. p. 88. ISBN 1-55832-329-5. 
  29. ↑ Handbook of Mushroom Poisoning: Diagnosis and Treatment. Boca Raton, Florida: CRC Press. 1994. p. 11. ISBN 0-8493-0194-7. 
  30. ↑ Canoe Country Flora: Plants and Trees of the North Woods and Boundary Waters. Minneapolis, Minnesota: University of Minnesota Press. 2004. p. 189. ISBN 1-57025-121-5. 
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  33. ↑ 33.0 33.1 Tylukti EE. (1987). Mushrooms of Idaho and the Pacific Northwest. Vol. 2. Non-gilled Hymenomycetes. Moscow, Idaho: The University of Idaho Press. pp. 9–10. ISBN 0-89301-097-9. 
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  35. ↑ "Giant mushroom found in Poland". BBC News. https://www.bbc.co.uk/news/world-europe-24292021. 
  36. ↑ Bill Bakaitis (2019). "Boletus huronensis: Comments on its toxicity with diagnostic images of its field characteristics and staining reactions". North American Mycological Association. https://namyco.org/boletus_huronensis.php. 
  37. ↑ Introductory Mycology. New York City: John Wiley and Sons. 1996. p. 495. ISBN 0-471-52229-5. 
  38. ↑ "Boletus edulis complex: from phylogenetic relationships to specific primers". Pagine di Micologia (30): 49–52. 2008. ISSN 1122-8911. 
  39. ↑ Beugelsdijk DCM; van der Linde S; Zuccarello GC; den Bakker; Draisma SGA; Noordeloos ME. (2008). "A phylogenetic study of Boletus section Boletus in Europe". Persoonia 20 (1): 1–7. doi:10.3767/003158508X283692. PMID 20467482. 
  40. ↑ "Molecular phylogenetics of porcini mushrooms (Boletus section Boletus)". Molecular Phylogenetics and Evolution 57 (3): 1276–1292. 2010. doi:10.1016/j.ympev.2010.10.004. PMID 20970511. http://static.msi.umn.edu/rreports/2010/211.pdf. 
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  42. ↑ "ITS primers for the identification of marketable boletes". Journal of Biotechnology 121 (3): 318–29. 2006. doi:10.1016/j.jbiotec.2005.08.022. PMID 16213623. 
  43. ↑ "PCR-based sensitive detection of the edible fungus Boletus edulis from rDNA ITS sequences". Electronic Journal of Biotechnology 11 (3): 1–8. 2008. doi:10.2225/vol11-issue3-fulltext-4. ISSN 0717-3458. http://www.bioline.org.br/pdf?ej08040. 
  44. ↑ Dentinger B (12 October 2013). "Nomenclatural novelties". Index Fungorum (29): 1. ISSN 2049-2375. http://www.indexfungorum.org/Publications/Index%20Fungorum%20no.29.pdf. 
  45. ↑ "What's for dinner? Undescribed species of porcini in a commercial packet". PeerJ 2 (2:e570): e570. 2014. doi:10.7717/peerj.570. PMID 25279259. 
  46. ↑ Cui, Yang-Yang; Feng, Bang; Wu, Gang; Xu, Jianping; Yang, Zhu L. (November 2016). "Porcini mushrooms (Boletus sect. Boletus) from China". Fungal Diversity 81 (1): 189–212. doi:10.1007/s13225-015-0336-7. http://groups.kib.cas.cn/klpb/yzl/tnh_fblw/201509/P020150928547013572278.pdf. 
  47. ↑ Volk T. (August 2004). "Boletus barrowsii, Chuck Barrows' bolete". Tom Volk's Fungus of the Month. Department of Biology, University of Wisconsin-La Crosse. http://botit.botany.wisc.edu/Toms_fungi/aug2004.html. 
  48. ↑ North American Mushrooms: a Field Guide to Edible and Inedible Fungi. Guilford, Conn: Falcon Guide. 2006. p. 392. ISBN 0-7627-3109-5. 
  49. ↑ Evenson VS. (1997). Mushrooms of Colorado and the Southern Rocky Mountains. Boulder, Colorado: Westcliffe Publishers. p. 157. ISBN 978-1-56579-192-3. https://books.google.com/books?id=EAeDeyqZLq0C&q=boletus%20edulis&pg=PA157. Retrieved 2009-10-20. 
  50. ↑ Arora D. (2008). "California porcini: three new taxa, observations on their harvest, and the tragedy of no commons". Economic Botany 62 (3): 356–75. doi:10.1007/s12231-008-9050-7. http://www.davidarora.com/uploads/arora_california_porcini.pdf. Retrieved 2009-11-04. 
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  52. ↑ "California Fungi: Boletus rex-veris". MykoWeb. http://www.mykoweb.com/CAF/species/Boletus_rex-veris.html. 
  53. ↑ Trudell, Steve; Ammirati, Joe (2009). Mushrooms of the Pacific Northwest. Timber Press Field Guides. Portland, OR: Timber Press. p. 217. ISBN 978-0-88192-935-5. https://books.google.com/books?id=WevHvt6Tr8kC. 
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  56. ↑ "Bolete productivity of cistaceous scrublands in northwestern Spain". Economic Botany 62 (3): 323–30. 2008. doi:10.1007/s12231-008-9031-x. 
  57. ↑ Taylor, Colin Duncan (2021) (in English). Menu from the Midi: A Gastronomic Journey through the South of France. Matador. ISBN 978-1-80046-496-4. 
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  88. ↑ "Some cases of intoxication probably caused by Sepedonium spp. infecting fruiting-bodies of some species of Boletus" (in it). Micologia Italiana 13 (1): 1/37–1/38. 1984. ISSN 0390-0460. 
  89. ↑ Bruns TD. (1984). "Insect mycophagy in the Boletales: fungivore diversity and the mushroom habitat". Fungus-Insect Relationships: Perspectives in Ecology and Evolution. New York, NY: Columbia University Press. pp. 91–129. ISBN 978-0-231-05695-3. 
  90. ↑ "Filamentous and polyhedral virus-like particle in Boletus edulis". Netherlands Journal of Plant Pathology 81 (3): 102–106. 1975. doi:10.1007/BF01999860. 
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  94. ↑ "Nutrient content in fungi as a primary food of the Red Squirrel Sciurus vulgaris L". Oecologia 64 (2): 230–31. 1984. doi:10.1007/BF00376875. PMID 28312343. Bibcode: 1984Oecol..64..230G. 
  95. ↑ "Fox Sparrow foraging on a king bolete mushroom". Northwestern Naturalist 87 (3): 252. 2006. doi:10.1898/1051-1733(2006)87[252:FSFOAK2.0.CO;2]. ISSN 1051-1733. 
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