broad. The degree to which the surface is covered with fine "hairs" is variable; these hairs are made of tangled hyphae and emergent thin-walled hyphal tips 2–5 µm in diameter, some even and smooth, some with granulated surfaces and some with moniliform walls (resembling a string of beads) that are irregularly thickened by hyaline bands that are 0.5–2 µm wide. The subpellis (the tissue layer immediately under the pellis) is abruptly differentiated from the pellis, 150–220 µm thick, and comprises interwoven, nearly hyaline, thin-walled hyphae 2–10 µm wide with scattered cells up to 15 µm wide. The gleba is made of hyaline, thin-walled, interwoven hyphae that are 2–7 µm broad with scattered cells that are inflated up to 15 µm. Similar species Tuber oregonense closely resembles T. gibbosum, which grows in the same habitats, but may be distinguished by the structure of its peridium, and differences in spores size and shape. Further, T. gibbosum grows from January to June. Another similar species in Elaphomyces granulatus. Edibility Tuber oregonense is a choice edible species. Its odor has been described as "truffly", a complex of garlic, spices, cheese, and "indefinable other essences"; the fungus is prized by commercial truffle harvesters and consumers for its intense fragrance. Because they grow in the topsoil and needles, they are considered to have a more "floral" and "herbal" flavor profile than related European truffles. Ecology, habitat, and distribution Like all Tuber species, T. oregonense is mycorrhizal. The fungus grows west of the Cascade Mountains from the southern Puget Sound region of Washington, south to southwestern Oregon at elevations from near sea level up to in pure stands of Pseudotsuga menziesii forests up to 100 years old, or Pseudotsuga mixed with Tsuga heterophylla, Picea sitchensis, or Alnus species. The species has been commercially harvested in the Pacific Northwest since the 1980s. and is often found in Christmas tree plantations as young as five years. The Oregon Truffle Festival, held in Eugene yearly since 2006 to coincide with the maturing of the truffle in late January, features activities such as cultivation seminars and truffle hunting excursions. Fruit bodies are produced from September through the middle of March. The fungus is an important component of the diet of northern flying squirrels, and comprises the majority of their diet at certain times of the year. Some individuals have claimed to have had success in growing the truffles in Christmas tree