FALSE TRUFFLES
We are regularly asked about “truffles” that people find in their gardens or out in the countryside, either partially buried or lying on the surface. They are occasionally true truffles, but most of the time they turn out to be false truffles — using the term in a gastronomic sense and reserving “true truffle” for species of the genus Tuber. Some of these false truffles can even be toxic. Never eat any fungus unless you are absolutely certain of its identity.
The most frequently encountered species are:
Scleroderma polyrhizum
This fungus begins its development underground, like true truffles, but eventually emerges through the soil surface to complete its growth and open in a star shape. It reaches a considerable size — up to 15 cm across before splitting — and is very firm and quite heavy. It is found in open, sunny locations, both at the edges of woodland and along roadsides and highways, where it is capable of pushing through asphalt. 
It is a widespread species, distributed across North America and Europe. We were recently asked about some false truffles from the Philippines that also turned out to be Scleroderma polyrhizum.
Confusion with true truffles arises when the fruiting bodies are still closed. In such cases it is necessary to cut the specimen in half to examine the interior. Scleroderma polyrhizum has a very thick, hard, brown skin (peridium). The interior (gleba) is purplish black, marbled with white veins. True truffles never have such a thick skin.
All Scleroderma species are considered toxic and can cause gastrointestinal disorders. In Spain they are listed in Annex D (species that may not be traded commercially) of Spanish Royal Decree 30/2009 of 16 January 2009, laying down the health conditions for the commercial trade of mushrooms intended for human consumption. (Spanish)
Scleroderma polyrhizum is the species most commonly confused with true truffles.
Pisolithus arhizus
Synonym Pisolithus tinctorius. Known in Australia as the “horse dung fungus” and in Germany as “Böhmische Trüffel” (Bohemian truffle). This fungus is sometimes confused with true truffles because of its initial underground growth. At this early stage it is very easy to identify by cutting it in half to examine the interior (gleba). 
Inside, the gleba is made up of numerous small chambers containing pea-sized spore packets (pseudoperidioles), which change in appearance and colour as they ripen: yellow at the base, blackish-brown and moist in the middle, and brown and powdery at the top.
The external appearance of Pisolithus arhizus is highly variable as it develops. In its final stage it resembles a powdery club that can reach 30 cm in height, supported by a pseudostipe formed from mycelial hyphae.
Pisolithus can grow in very arid conditions and is frequently found along roadsides and highways, emerging through gravel or asphalt. It is widely distributed throughout the world.
Pisolithus arhizus has been used as a natural dye and is considered edible when young, though we have never tasted it ourselves — its appearance is not exactly inviting.
Choiromyces meandriformis
FULL DESCRIPTION. In northern Europe it is known as Choiromyces venosus and regarded as an excellent edible species. In southern Europe, however, it is considered toxic (a gastrointestinal irritant). In Spain it is listed in Annex D (species that may not be traded commercially) of Spanish Royal Decree 30/2009 of 16 January 2009, laying down the health conditions for the commercial trade of mushrooms intended for human consumption.
Specimens are frequently found partially protruding from the soil in summer and autumn, and can reach a large size. Choiromyces meandriformis grows in acid soils with high rainfall and prefers clayey substrates. 
We have found it in Navarre associated with Quercus robur and in Hungary under Picea abies.
Whitish to yellowish-brown, with reddish patches at maturity, and often quite irregular in shape. The interior is white to cream or yellowish-brown, marbled with sterile, white meander-like veins — the origin of the name meandriformis — which surround the fertile tissue.
The odour is strong and distinctive, becoming unpleasant in fully mature specimens.
Owing to its large size and whitish appearance, Choiromyces meandriformis is sometimes sold fraudulently as “white truffle” on account of its superficial resemblance to Tuber magnatum, though its texture, aroma and flavour are entirely different. In Spain, specimens imported from Eastern Europe and incorrectly labelled as Tuber magnatum occasionally appear on the market.
Choiromyces magnusii
FULL DESCRIPTION. This species is highly prized in parts of Extremadura and Andalusia, where it is known as “criadilla jarera” and eaten as a local delicacy. It is a spring species that grows in acid soils and is found exclusively under Cistus ladanifer. Although it develops underground, 
its presence can be detected by the cracks it pushes up in the soil as it grows. It reaches a large size — up to 10–12 cm — and is whitish to light brown, very irregular in shape, gibbose and deeply grooved, which makes it very difficult to clean before cooking. The interior is white to brown depending on maturity, marbled with white, sinuous sterile veins that do not fully enclose the fertile areas.
The odour is faint but distinctive.
A gastronomic fair dedicated to this “truffle” has been held for many years in El Almendro (Huelva, Spain) each April. There it is known as “turma” and “trufa blanca de El Andévalo”.
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Antonio Rodríguez trufamania@gmail.com antonio@trufamania.com |