If a fungus is the symbol of Cahors region and wines of Cahors, this is the black truffle.
At the beginning of last century, more than 200 tons were traded each year on the Lalbenque market near Cahors. Production is now in hundreds of pounds for this "black diamond" who lives in symbiosis on the roots of oak trees known as "truffiers" (such as Quercus pubescens) which grow on limestone soil and gave their name to our region: the Quercy.
The aroma of truffle, often associated with notes of mushroom and under woods, is sign of great wines of Cahors. The aroma is formed during ageing in the bottle, so you will find it in old vintages, as the Château Paillas vintage 1995.
More technical information about the truffle on wikipedia: http://en.wikipedia.org/wiki/Truffle_(fungi)
For truffle lovers, the website of Jacques and Pierre-Jean Pebeyre, truffles traders: http://www.pebeyre.fr/