The part of the fungus used as food is the ascoma, the fruiting body of the fungus. The best-known truffles are the black, Tuber melanosporum, and the white, T. magnatum, both found chiefly in W Europe. Some are canned for export. Besides the well-known white and black truffles, there are hundreds of other species, all mycorrhizae, fungi in a symbiotic relationship with plant roots. The tasty Oregon white truffle, T. gibbosum, for example, grows only on the roots of the Douglas fir tree, which is dependent upon the fungus for its mineral nutrition.
Truffles are widespread in distribution and are found in a wide variety of habitats.
The Columbia Encyclopedia, Sixth Edition.