All mushrooms, based on the way in which they absorb organic substances, are divided into three large groups:
The group of mushrooms that has the greatest interest is undoubtedly the third, namely that of the symbionts, including the species of greatest culinary interest and therefore of greatest value. For example, the “royal mushroom” or “good egg” (Amanita caesarea) and the “porcino” (Boletus edulis) belong to this group, but above all the highly prized truffles (Tuber spp).
Truffles must necessarily live in symbiosis with tree plants to produce the precious sporocarp so appreciated by gourmets. The exchange of substances between the two partners takes place at the root level in particular formations called mycorrhizae, which are structured in a characteristic way for each species. In general it is a sleeve (mycoclene) formed by 5-6 layers of septate tubes called hyphae, which with a stratified intertwining wrap the apexes of the terminal rootlets of the tree and, insinuating themselves between the first layers of root cells, form a reticulum (Hartig’s reticulum), at this level the plant offers the fungus, in addition to other substances (probably amino acids and hormonal substances), carbon hydrates (sugars) in exchange, mainly, for water and mineral salts. From this meeting point many hyphae branch off which, taken together, take the name of mycelium. The latter, branching into the ground, also spreads several meters away, in search of nutrients.
At the right time, that is when all the necessary environmental conditions and structures are created, some hyphae intertwine and give rise to the formation of the fruiting body, in whose gleba the spores differ. These, germinating, will give rise to a new mycelium which will be able, by joining with the young apexes of the roots, to form new mycorrhizae.