Boletus edulis

Appearance

The cap of this mushroom is 7–30 cm 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 in height, and up to 7 cm thick—rather large in comparison to the cap; 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 deep, and whitish in colour when young, but mature to a greenish-yellow. The angular pores, which do not stain when bruised, are small—roughly 2 to 3 pores per millimetre. In youth, the pores are white and appear as if stuffed with cotton ; 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. Fully mature specimens can weigh about 1 kg ; a huge specimen collected on the Isle of Skye, Scotland, in 1995 bore a cap of 42 cm , with a stipe 18 cm in height and 14 cm wide, and weighed 3.2 kg . A similarly sized specimen found in Poland in 2013 made international news.

''B. edulis'' is considered one of the safest wild mushrooms to pick for the table, as no poisonous species closely resemble it. The most similar poisonous mushroom may be the devil's bolete , 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.

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. ''B. edulis'' has pleurocystidia 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. The hyphae of ''B. edulis'' do not have clamp connections.

Naming

Common names for ''B. edulis'' vary by region. The standard Italian name, ''porcino'' , means ''porcine;'' ''fungo porcino'', in Italian, echoes the term ''suilli'', literally "hog mushrooms", a term used by the Ancient Romans and still in use in southern Italian terms for this species. The derivation has been ascribed to the resemblance of young fruit bodies to piglets, or to the fondness pigs have for eating them. It is also known as "king bolete". The English ''penny bun'' refers to its rounded brownish shape. The German name ''Steinpilz'' refers to the species' firm flesh. In Austria, it is called ''Herrenpilz'', the "noble mushroom", while in Mexico, the Spanish name is ''panza'', meaning "belly". Another Spanish name, ''rodellon'', means "small round boulder", while the Dutch name ''eekhoorntjesbrood'' means "squirrel's bread". Russian names are ''belyy grib'' and ''borovik'' .
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, ultimately from the Latin ''cippus'' "stake". ''Ceppatello'', ''ceppatello buono'', ''ceppatello bianco'', ''giallo leonato'', ''ghezzo'', and ''moreccio'' are names from Italian dialects, and ''ciurenys'' or ''surenys'' is another term in Catalan. The French-born King Charles XIV John popularised ''B. edulis'' in Sweden after 1818, 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. The Finnish name is ''herkkutatti'', ''herkku'' from ''herkullinen'', which means delicious, and ''tatti'', describing the type of mushroom.Several similar brownish-coloured species are sometimes considered subspecies or forms of this mushroom. In Europe, in addition to ''B. edulis'' , the most popular are:
⤷ ''Tête de nègre'' , much rarer than ''B. edulis'', is more highly regarded by gourmets, and more expensive. Usually smaller than ''B. edulis'', it is also distinctively darker in colour. It is especially suited to drying.
⤷ ''Cèpe des pins'' 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.
⤷ ''Cèpe d'été'' , also less common and found earlier.

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'' were described in 2013 as ''B. bainiugan'', ''B. meiweiniuganjun'' and ''B. shiyong''.


Western North America has several species closely related to ''B. edulis''. The white king bolete , found in parts of Colorado, New Mexico, Arizona, and California , is named after its discoverer Chuck Barrows....hieroglyph snipped... It is lighter in colour than ''B. edulis'', having a cream-coloured cap with pink tones; 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''. The California king bolete 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. The queen bolete , 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. The spring king bolete , 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.

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 , spruce , hemlock and fir 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, to an altitude of 3,500 m . In northwestern Spain, they are common in scrublands dominated by the rock rose species ''Cistus ladanifer'' and ''Halimium lasianthum''.

''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 China, the mushroom can be found from the northeastern Heilongjiang Province 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.

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 stomach ache 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 larvae. 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".

''Boletus edulis'' is a food source for animals such as the banana slug '''', the long-haired grass mouse, the red squirrel, and, as noted in one isolated report, the fox sparrow.

Uses

''Boletus edulis'', as the species epithet ''edulis'' 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. 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''.
''sunt tibi boleti; fungos ego sumo suillos''

wrote the disgruntled Martial when served ''suilli'' instead of ''boleti''. The term ''suilli'' was also thought to encompass the related ''Leccinum scabrum''.

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 , 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. The fruit bodies are highly perishable, due largely to the high water content , 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 bioaccumulate toxic heavy metals like mercury, cadmium, caesium and polonium. 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, and for long-term radioecological monitoring of polluted areas.


Porcini are sold fresh in markets in summer and autumn in Central and Southern Europe, and dried or canned at other times of the year, and distributed worldwide to countries where they are not otherwise found. 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. Porcini are a feature of many cuisines, including Provençal, and Viennese. They are used in soups and consumed blanched in salads in Thailand. 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. They are also one of the few mushroom species pickled and sold commercially.