Identification
The primary truffle found under pecan trees is Tuber lyonii (=T. texense), although as just discussed there are other similar species currently being described. This is the same genus, but 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. We have found it in association with oaks or other members of the Fagales. The color of individual specimens varies from light to dark brown. These 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.
Truffle Hunting
They are usually found in well-irrigated orchards, although not always, and have been found around solitary volunteer pecan trees in fence rows and other odd locations. They tend to be in more crowded, shaded sections of the orchard. We have found them on numerous varieties of pecans, but since pecans are grafted, most have very similar root stocks. Based on the orchards where they were originally found, we assumed they preferred heavier clay soils. However, in more recent years we have found them in abundance in some orchards with a much lighter, sandier soil (including the flat woods soils of the eastern coastal plain). Our recent studies have shown these truffles to be favored by higher soil pH, just as many other species of Tuber are. The fungus grows in a mycorrhizal relationship with the pecan tree roots. Although they obtain some nutrition from the tree, they also help the tree get needed minerals from the soil and are therefore beneficial to the tree (a true win-win situation). The truffles themselves will be found unattached in the top inch or two of soil, although they are connected to the tree via very thin hyphae that are not visible. 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. They will sometimes protrude slightly from the soil surface and require no digging. We have found truffles by simply returning to areas known to produce them and 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 the abundance of wild hogs in the area are obviously attracted to truffles based on the rooting evident in many orchards with truffles.) Truffles can be seen sometimes following pecan harvest where the sweepers have swept the soil surface, and they can even be found among the harvested pecans.
Guidelines for Eating
These truffles are certainly 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. This would be mitigated to some degree by the fact that they grow underground. Also, the small quantities consumed would reduce the potential risk, but this has not been thoroughly evaluated.
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 arachis@uga.edu, or samples can be mailed to the following address:
Dr. Tim Brenneman
Dept. of Plant Pathology
University of Georgia, Tifton Campus
115 Coastal Way
Tifton, GA 31793