Not all fungi growing underground are "prized truffles"
Summary: The term “truffle” is often used for any globular fungus growing below the soil surface. Strictly speaking, the term “truffle”, or “true truffles” refers to a defined group of prized and fragrant fungi belonging to the Tuber genus. Well-known individuals in this group include for instance white and black truffles served in high-end restaurants. The group is also much more diverse than one might think, as more than 180 “true truffle” sorts might exist throughout the world. “False truffles” are made from various fungal groups and are genetically distinct from “true truffles”. Many “false truffles” are also edible, and some possess a unique flavor, highlighting the flavor diversity of the fungal kingdom.
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Fungi are so different from plants and animals that they are classified in their own group or “kingdom”. Other well-known kingdoms include for instance animals (Animalia), plants (Plantae), or bacteria (Bacteria). Whereas there are 374 thousand known plant species on our planet, the number of fungal species might be significantly higher. Indeed, it is estimated that there might be 40 times more fungi than plants.
Fungi are extremely varied in shape and size. Some well-known examples include molds, yeast (i.e. baker yeast) and mushrooms (i.e. Champignon), the fleshy fruiting body of a fungus that is typically produced aboveground. Truffles, based on their lifestyle (belowground) and biology, are classified as fungi and not as mushrooms.
The term “truffle” is often used for any globular fungus found below the soil surface. Prized truffles (i.e. the white truffle found in Italy and Eastern Europe) are nevertheless distinct from “false truffles” (i.e. the desert truffles of Morocco) and genetically, “true” & “false” truffles differ from each other as much as an apple differs from a banana.
So how many "true truffle" sorts do actually exist?
Before the advent of DNA-based molecular techniques (before 1990), truffle species were distinguished from each other by observing the morphology of truffle spores under a microscope (example here). It is estimated that approximately 60 “true truffle” species could be identified through spores’ morphology by 1990.
Morphology-based identification is however not bulletproof, as a certain level of variation in spores’ morphology can naturally happen. This created confusion for truffles when the mycologists Carlo Vittadini and Adolphe Chatin respectively named in 1831 and 1892 the same truffle species as Tuber aestivum and Tuber uncinatum.
Starting in 1990, molecular techniques became widespread in research laboratories, enabling to “read” the alphabet that makes up the genetic code of organisms. As expected, these molecular techniques turned out to be superior to classify species compared to traditional morphology-based approaches. Molecular techniques for instance demonstrated that the truffles Tuber uncinatum and Tuber aestivum were indeed a single species.
A meta-analysis published in 2010 relying on 76 independent DNA-based studies, estimated that at least 180 true truffle species might exist worldwide. This prediction is corroborated by the regular description in the last decade of novel truffle species in scientific literature (i.e. new Mexican and Japanese true truffles species).
Are other fungi that grow underground edible?
It is estimated that 5% of mushrooms are poisonous. By contrast, the exact percentage of potentially poisonous fungi growing belowground is unknown. This might be due to the fact that belowground fungi are simply less studied because they are not easily found!
The false truffle Choiromyces venosus is considered edible in Sweden. Yet its consumption is forbidden in many southern European countries, based on the belief that it might be poisonous, even though no poisoning for a century has been reported in Sweden. Studies are currently underway to assess its safety/ toxicity.
In the case of true truffles (Tuber genus), the lack of toxin encoding regions in the genome of commercially relevant species (i.e. the black truffle Tuber melanosporum) highlights that they are safe for consumption. This is corroborated by a long history of safe consumption by humans dating back to the middle-ages. Nevertheless, “true” truffles are also heavily colonized by microbes, and these microbes can be harmful if the truffles are no longer fresh. In conclusion, as with other fungi, “true” truffles should only be consumed from reliable/safe sources that guarantee their safety and freshness.
Edible “false truffle” species include for instance the desert truffle, the Oregon black truffle, and the honey truffle. Desert truffles (i.e. genus Terfezia) do not have a strong flavor. Indeed in Morocco, where desert truffles are commonly found, they are used in dishes as flavor catchers for other ingredients, a bit like potatoes in western cuisine. By contrast, Oregon black truffles, typical in the pacific northwest of the USA, have a musty and pungent flavor. The honey truffle, as its name indicates, has a honey flavor with some nutty notes, and it is predominantly collected in the Carpathian Basin.
Why is this relevant?
Understanding that not all fungi growing underground are prized/“true” truffles matters both in terms of food safety and culinary experience. Indeed, some fungi might be poisonous, so it is always essential to rely on experts to know if a fungus is edible or not. Some edible “false truffles” might also offer an exceptional sensory experience that is quite different from “true” truffles, so just be open about it!
Written by Richard Splivallo
Richard is the CEO of Nectariss and a truffle expert. As a former university professor, he has dedicated almost 20 years of his life to better understand the complex biology of truffle fungi and has authored more than 25 scientific publications on that topic.