Summary:
Underground fruitbodies are spherical to irregular, furrowed, white becoming orange-brown to reddish brown, the surface roughened-bald to minutely downy, when old often cracking. The interior is solid, white to brown with white marbling veins. Odor is mild, soon becoming pungent and complex (garlic, spices, cheese, and indefinable other essences). Fruiting is from fall to winter. Four known species occur in the Tuber gibbosum complex, separated most reliably by the size and shape of the alveolate spores (also by molecular techniques): Tuber oregonense and T. bellisporum have narrow spores with those of the latter shorter, while Tuber gibbosum and T. castellanoi have wider spores with those of the latter shorter. Tuber oregonense is characterized within the complex by its long narrow spores common in 1- to 4-spored asci (subfusoid in the largest spores), its generally taller spore ornamentation, and its generally prosenchymatous peridial pellis. "Immature specimens of all four species may have poorly developed peridia with only scattered inflated cells and few or no one- and two-spored asci, so they often cannot be dependably separated at immature stages by morphology alone." Tuber oregonense fruits primarily in fall to early winter and is the most commonly collected Tuber species in the fall in the Pacific Northwest. (Bonito). [Even in mature specimens there is considerable variation in spore size and shape, and the size depends on how many spores are in the asci, making determination time-consuming.] Tuber gibbosum complex distinguished from other Tuber species by growth with Douglas-fir, relatively large size (when mature), tendency to develop cracks when old, and strong garlicky odor (when present). (Arora) The Tuber gibbosum complex is distinguished microscopically from other Tuber species in having the mature peridial suprapellis with "scattered to abundant tangled hyphae and hyphal tips" with walls irregularly thickened up to 2 microns in bands to produce a beaded appearance, these structures most evident at maturity. (Bonito)

Interior:
solid, when young "the fertile tissue whitish and marbled with mostly narrow, white, hypha-stuffed veins that emerge here and there through the peridium to its surface", when mature, "the fertile tissue light brown to brown from the color of the spores but the marbling veins remaining white", (Bonito), spore mass firm, "white when immature, brown with white marbling when mature", (Trappe, M.), spore mass whitish at first, then becomes brownish with white marbling, (Trudell)

Odor:
mild when young, ''soon becoming strong, pungent and complex, "truffly"'', (Bonito), ''"truffly," a complex of garlic, spices, cheese, and indefinable other essences'', (Trappe, M.)

Microscopic:
spores elliptic to subfusoid with narrowed ends, light brownish golden, excluding ornamentation in 1-spored asci 42.5-62.5 x 17.5-30 microns, Q=1.55-2.5(2.9), in 2-spored asci, 32.5-50 x 15-25 microns, Q=1.5-2.4, in 3-spored asci 27.5-45 x 15-25 microns, Q=1.5-2.0(2.45), in 4-spored asci 25-38.5 x 13-28 microns, Q=1.4-2.2(2.3), in 5-spored asci 28-34 x 22-25 microns, Q=1.3-1.4, spore wall 2-3 microns thick, ornamentation "an orderly, alveolate reticulum", the alveolae 5-6-sided numbering 5-8(9) along the spore length, the corners forming spines (4)5-7(8) microns long and 0.5 microns wide, somewhat wider at base, the alveolar walls as tall as the spines; asci 1-4(5)-spored, when young spherical to broadly ellipsoid to ovoid or pyriform [pear-shaped], when mature spherical to broadly ellipsoid or misshapen from spore pressure, colorless, thin-walled, without stalk when mature but sometimes base narrowed stalk-like when young up to 15 x 7 microns; pellis of peridium generally prosenchymatous, 200-300 microns thick plus or minus 80 microns, of tightly interwoven hyphae 3-5(10) microns wide, the cells short and with nearly colorless walls 0.5-1.0 microns thick, "where the interior veins emerge through the peridium the cells often forming a localized tissue of rounded cells" up to 12 microns wide, (Bonito), spores 25-52 x 17-40 microns, elliptic or tapered to a tip at both ends, with honeycomb ornamentation, (Trappe, M.)

Notes:
Tuber oregonense is found west of Cascade Mountains from southern Puget Sound of WA south to southwestern OR. (Bonito), and Beug(3) gives the range as BC to CA. Berch(4) lists two fruitbody collections from BC.

EDIBILITY

commercially harvested for culinary use (Bonito)