The truffle found under pecan trees is Tuber lyonii (=T. texense). It is the same genus but a different species as the very expensive white or black truffles found in Europe. It has been found under pecans in Georgia, Florida, Texas, and New Mexico, but this truffle has been found on other tree species across eastern North America from Mexico to Canada. The color of individual specimens varies from light to dark brown. Truffles have a range of sizes, from the diameter of a buckshot up to the size of a golf ball (occasionally larger). Some will be round but most will have lobes and irregularities. The interior will be very firm, lighter in color, and have a conspicuously "marbled" appearance with alternating streaks of brown and white. They will also have a very strong earthy aroma.
They are usually found in well-irrigated orchards, particularly after a dry year such as 1999. They tend to be in more crowded, shaded sections of the orchard. We have found them on numerous varieties of pecans, but often in heavier clay soils. The fungus grows in a mycorrhizal relationship with the pecan tree roots, but the truffles will be found unattached in the top inch or two of soil. They may be adjacent to the trunk or anywhere out to about the drip line of the tree. Areas devoid of vegetation such as herbicide strips in managed orchards are easier to search. We have found truffles by simply raking the surface of the soil with a stiff-tined garden rake. Of course, a trained dog or pig would help since they are not usually visible above ground! (Note: pigs are not used in south Georgia for truffle hunting, but are used in Europe.) Truffles can be seen sometimes following pecan harvest where the sweepers have swept the soil surface.
Guidelines for Eating
These truffles are generally considered edible, but as with any wild mushroom it is an "eat at your own risk" situation. Specimens should be fresh and have a firm texture. Avoid older, darkened specimens, especially if they are noticeably softer than usual. Truffles from managed pecan orchards that have been sprayed regularly may have low levels of pesticide residue. The small quantities consumed would reduce the potential risk, but this has not been thoroughly evaluated. One pesticide that should be avoided is aldicarb (Temik). This insecticide is highly toxic and is applied directly to the soil. DO NOT CONSUME TRUFFLES FROM ORCHARDS TREATED WITH TEMIK.
There are also other fungi that can be mistaken for truffles. Puffballs are the most common. Features that distinguish them from truffles include the fact that they usually are uniformly round or pear-shaped and grow above ground. They also are often white and will have a sterile base or stalk. Fortunately puffballs are generally edible also, except for the genus Scleroderma which will be purple when cut open.
Potentially the most serious case of mistaken identity would be to consume a mushroom "button" (ie. small, unexpanded mushroom) from a highly poisonous species such as Amanita. Slicing the specimen in half will reveal the stalk and cap instead of the uniformly marbled interior of a truffle.
As with any fungus, it is important to know what you are eating as some species are highly toxic. If you would like assistance in identifying truffles, images can be submitted electronically to firstname.lastname@example.org, or samples can be mailed to the following address:
Dr. Tim Brenneman
Dept. of Plant Pathology
University of Georgia
P.O. Box 748 Rainwater Road
Tifton, GA 31793