Summary:
The underground fruitbodies are spherical to irregularly lobed and furrowed, colored pale olivaceous to olive brown to dull brown or orange-brown, the surface downy and often cracking, the interior solid, whitish to brown, with white marbling veins. Odor is mild soon becoming strong, pungent and complex, "truffly". Fruiting is known from January to June, under Douglas-fir. Microscopic features are important in differentiating T. gibbosum from other members of the T. gibbosum complex. Four known species occur in the Tuber gibbosum complex in the Pacific Northwest, 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 gibbosum is characterized within the complex by fairly wide elliptic spores of intermediate length, and a peridium of pseudoparenchymatic tissue. Of the four species only T. gibbosum forms a well-developed, epithelial pellis of large, inflated cells - "this is usually evident in fairly young specimens". "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." (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.] The Tuber gibbosum complex is distinguished from other Tuber species by growth with Douglas-fir, relatively large size (when mature), a tendency to develop cracks when old, and a 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). The descriptions of Smith(4), Arora(1), and Gilkey(3) would encompass both Tuber gibbosum and Tuber oregonense.

Interior:
solid, when young whitish and marbled with mostly narrow, white, hypha-stuffed veins that emerge through the peridium at furrows, when mature light brown to brown from spores but marbling veins remaining white, (Bonito), spore mass "white when immature, brown with white marbling when mature", (Trappe, M.(3)), more or less solid; "dark purple-brown to brick red marbled with white", (Smith), "solid, marbled, crisp; whitish when young, the fertile tissue becoming brown to dark brown to brick-red when mature, the meandering sterile veins remaining whitish", (Arora), "wood brown" to "brick red" when mature, marbled by distinct shining white veins, (Gilkey)

Odor:
mild when young, soon ''strong, pungent and complex, "truffly"'', (Bonito), ''"truffly", a complex of garlic, spices, cheese, and indefinable other essences'', (Trappe, M.(3)), usually strong and garlicky when fully mature (Arora)

Taste:
as odor (Bonito), mild but like garlic when mature (Miller)

Microscopic:
spores elliptic to broadly elliptic, light brownish golden, excluding ornamentation in 1-spored asci 36-60 x 25-37.5 microns, length to width ratio Q=1.2-1.8, in 2-spored asci, 28.5-50 x 20-37.5 microns, Q=1.1-1.8, in 3-spored asci 25-50 x 16-32.5 microns, Q=1.2-1.9, in 4-spored asci 22.5-38 x 17-30 microns, Q=1.1-1.8, in 5-spored asci 25-32 x 19-24 microns, Q=1.30, spore wall 2-5 microns thick, ornamentation "an orderly, alveolate reticulum", the alveolae 5-6-sided numbering (6)7-10 along the spore length, the corners forming spines 3-4(5) microns long and 0.5 microns wide, much wider at base, "the alveolar walls as tall as the spines"; asci (1)2-4(6)-spored, when young spherical to broadly ellipsoid to ovoid or pyriform [pear-shaped], when mature spherical to broadly ellipsoid, sometimes cylindric or misshapen from spore pressure, colorless, thin-walled when young, walls +/- 1 micron thick when mature, 73-100 x (35)65-75 microns, without stalk when mature; pellis of peridium pseudoparenchymatic, 60-100 microns thick, of several tiers of colorless to nearly colorless or yellowish, isodiametric cells 5-20 microns wide and some intermingling hyphae 3-5(10) microns wide, "near the suprapellis with much thickened and refractive walls", (Bonito), spores 25-45 x 17-33 microns, elliptic with bluntly rounded ends, honeycomb ornamentation; short emergent hyphae from furrows having peculiar, bead-like wall thickenings, (Trappe, M.(3)), spores 35-52 x 17-39 microns, long elliptic, alveolate-reticulate, dark yellowish brown; asci 1-6(8)-spored, saccate to pyriform, (Smith), 35-52 x 17-40 microns, "elliptical or elongated, reticulate-alveolate (ridged and pitted with shallow depressions) when mature but smooth when very young", dark yellow-brown to brown when mature, asci mostly 1- to 6-spored, randomly embedded in tissue between veins, (Arora), spores 35-52 x 17-40 microns, mostly long-elliptic, generally rounded at the ends, alveolate with the "spore surface reticulate beneath the alveoli", with 7-10 x 5-9 alveoli across diameter of spore, spores dark yellowish brown; asci 1-6-spored, rarely 7-spored or 8-spored; "venae externae loose, spongy, generally opening in the surface depressions filled with irregular hairs"; "outer cortical layer pseudoparenchymatous, the superficial cells often forming branched, knotted hairs more or less parallel with the surface", (Gilkey)

Notes:
Tuber gibbosum in the new strict sense occurs west of the Cascade Mountains from southern Vancouver Island in BC, south through western WA and OR to northwestern CA''s San Francisco Bay. (Bonito). Berch(4) lists a fruitbody collection from BC.

EDIBILITY

choice, but widespread collecting can be destructive, (Arora), commercially harvested for culinary use (Bonito), toxic in a 2010 report: stomach queasy, diarrhea (4x), later fainted (3x), felt cold: consumed brie infused/odor of truffle, (Beug)

Synonyms and Alternate Names:
Merulius rufus Pers.
Phlebia acerina Peck
Tuber giganteum Gilkey