Common name: Michigan truffles
Description and identifying characteristics: This truffle is brick red at maturity, but can range in color. Although variable in size, it can produce quite large fruiting bodies, often composed with a few lobes. The outer surface or peridium of the truffle has a texture of small warts. A cross-section through the truffle shows a marbled fertile body, or gleba. With a microscope ascospores with honey-combed surface ornamentation can be observed, often with 2 of these round spores packed in each sac or ascus. These truffles fruit across the Midwestern and Northeastern US, in associate with spruce and pine, but also in mixed forests including those with oak, hickory, and birch. Truffles begin to mature in the fall and into winter and are best collect with the aid of a trained truffle dog to ensure their quality, commercial value, and sustainability.
Fruiting bodies are comprised of one to several lobes. Individual truffles are oval in shape, may be irregular and depressed, and range from 2–12 cm across. Mature, ripe and choice fruiting bodies are characterized by a sweet but slightly musty odor that grows stronger with time. A cross-section through the truffle will be veined through a dark gleba due to the matured pigmented ascospores. Overly mature truffles are slimy or fuzzy and should be left in the field to rot.
Tuber belongs to the phylum Ascomycota, which means that their spores are produced in sacs called asci. In Tuber canaliculatum 2-spored asci are most frequently observed. However, 1-, 3- and 4- spored asci are also sometimes present. These spores are globose in shape, or slightly ellipsoid, and are quite large at 42-60 um x 40–55 um (excluding the honeycombed ornamentation on the outer surface of the spore wall).
Ecology/associated host or habitat: Tuber canaliculatum, and other Tuber species, are ectomycorrhizal fungi. These fungi grow in a mutualistic association with the roots of living trees, including eastern white pine (Pinus strobus) providing them with nutrients and water in exchange for carbohydrates. While the ectomycorrhizal structures may be seen on the roots of their host plant appear as swollen, caramel brown in color, this character will not help in field identification. In the Midwest of America, ripe truffles occur from August–November.
Poisonous Look-alikes: While there are many species of truffles in the mid-west, there are no reasonable look-alikes to this truffle. The combination of its reddish color, warted surface ornamentation, firm waxy texture and veined gleba distinguish this truffle from others in the region. The gleba, or fertile inner tissue of T. canaliculatum is also darker in mature fruiting bodies than other Tuber species native to North America. There are many different kinds of native truffles but Tuber canaliculatum can be easily distinguished from them. For instance, Scleroderma truffles are commonly found, and should not be eaten. Scleroderma have a very thick and hard outer peridium and produce a powdery-spore inside upon maturity, rather than veined as in Tuber.
Methods and Tips on harvesting: Use a truffle dog to survey and locate truffle patches. Collect whole and mature fruiting bodies. Leave rotten, partially rotten and immature fruiting bodies in the ground. It is best to clean specimen in the field by gently brushing away any dirt or detritus with a mushroom brush, leave intact and out of the sun (in a cooler is best). Truffle patches will remain productive for years, if responsibly harvested and managed, so be responsible and note GPS coordinates of productive patches for future harvests.
Possible allergic reactions and symptoms: Tuber Tuber species have evolved to be eaten and dispersed by small mammals, and consequently, are hypoallergenic to humans. However, problems can arise when bacteria and molds growing on old, rotten or infected truffles are consumed. If truffles are slimy, sticky, mushy, or smell particularly bad, they should not be harvested, sold or consumed.
Special considerations for storage. Because truffles grow underground it is important to remove soil and debris from the outer surface of these fungi, an especially important detail in relation to interstate / international trade. A synthetic fiber brush (equivalent thickness of a medium toothbrush) is used to remove as much soil as possible. Moist cotton fabric can be helpful in clean up truffle fruiting bodies prior to sale. Before consuming truffles always use a truffle brush and clean under running water and then remove excess water with cotton cloth or paper towel.
Truffles are often stored at 4 degrees C in jars or containers that do not allow gas exchange. They may be wrapped in a cloth, paper, or in rice to prevent water films from forming through condensation during the truffle during storage, which act as sites of fermentation and truffle spoilage. Replace wrapping material every 2 days. Truffles are best consumed within 1 week of harvest.
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References:
Michigan Truffles
Bonito, G., M. E. Smith, M. Nowak, R. A. Healy, G. Guevara, E. Cazares, A. Kinoshita, E. R. Nouhra, L. S. Dominguez, L. Tedersoo, C. Murat, Y. Wang, B. A. Moreno, D. H. Pfister, K. Nara, A. Zambonelli, J. M. Trappe, and R. Vilgalys. 2013.Historical Biogeography and Diversification of Truffles in the Tuberaceae and Their Newly Identified Southern Hemisphere Sister Lineage. PLOS one 8.
Gilkey, H. M. 1925. Five new hypogeous fungi. Mycologia 17:250-255.
Miller, O.K., H. H. Miller (2006) North American Mushrooms: A Field Guide to Edible and Inedible Fungi. Falcon Guides.