What You Should Know
Tuber oregonense is roughly round with a dirty stone-colored surface that becomes darker brown with age. It is smooth but furrowed and its translucent flesh is pale gray, marbled with white veins. Oregonians have an opaque whitish to yellowish or olivaceous peridium that develops prominent reddish-orange to cinnamon colors. The gleba initially is whitish, then becomes brownish with white marbling. The odor is complex and has been described as a mix of garlic, spices, cheese, and other indescribable components.
Tuber oregonense belongs to a group of closely related species known as the Tuber gibbosum clade, which includes Tuber gibbosum, T. castellanoi, and T. bellisporum. All four species occur in California. They are nearly indistinguishable macromorphologically, differing subtly in spore morphology and molecular sequences. All form white fruit bodies that discolor yellowish-brown, orangish-brown or reddish-brown, with a solid gleba marbled from sterile white veins and pale brown to reddish-brown fertile tissues.
Other names: Oregon White Truffle.
Tuber oregonense Mushroom Identification
The fruit bodies of T. oregonense are hypogeous (growing in the ground), typically 0.5–5 cm (0.2–2 in) broad, although specimens up to 7.5 cm (3 in) have been recorded. Smaller specimens are spherical or nearly so, and have random furrows; larger specimens are more irregular in shape, lobed and deeply furrowed. Young fruit bodies have a white peridium, as the truffle matures it develops red to reddish-brown or orangish-brown patches; with age, it becomes orange-brown to reddish-brown overall and often develops cracks on the surface.
The peridium is 0.2–0.4 mm thick, and the surface texture ranges from relatively smooth to covered with tiny "hairs" that are denser in the furrows, and more scattered on the exposed lobes.
The gleba is solid; in youth, the fertile tissue is whitish and marbled with mostly narrow, white, hypha-stuffed veins that emerge throughout the peridium to its surface. In maturity, the fertile tissue is light brown to brown from the color of the spores, but the marbling veins remain white.
The odor and flavor of the flesh are mild in youth, but soon become strong, pungent and complex, or "truffly".
The spores are ellipsoid to somewhat spindle-shaped with narrowed ends, and light brownish. The size of the spores varies depending upon the type of asci in which they develop: in one-spored asci they measure 42.5–62.5 by 17.5–30 µm; in two-spored asci they are 32.5–50 by 15–25 µm; in three-spored asci they are 27.5–45 by 15–25 µm; in four-spored asci they are 25–38.5 by 13–28 µm; in five-spored asci 28–34 by 22–25 µm (all sizes excluding surface ornamentation). The spore walls are 2–3 µm thick and are covered with a honeycomb-like (alveolate) network. The cavities of the honeycomb typically have five or six sides, and the corners form spines that are 5–7 µm tall by 0.5 µm thick.
The peridiopellis (the cuticle of the peridium) is 200–300 µm thick plus or minus 80 µm of tightly interwoven hyphae that are 3–5 (sometimes up to 10) µm broad. The cells are short and have nearly hyaline walls that measure 0.5–1 µm thick; the interior veins emerge through the peridium the cells and often form a localized tissue of rounded cells up to 12 µm broad.
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 spore's size and shape. Further, T. gibbosum grows from January to June. Another similar species in Elaphomyces granulatus.
Tuber oregonense Taxonomy and Etymology
The species was first officially described and named in a 2010 Mycologia article, although T. oregonense had been previously used provisionally (as Tuber oregonense Trappe & Bonito) in American field guides and other popular publications for several years. The type specimen was collected from Benton County, Oregon, on 3 February, 2007 along U.S. Route 20 in Oregon.
The specific epithet oregonense derives from the name Oregon and the Latin suffix -ense (relating to), about western Oregon being its central region of abundance. The fungus is commonly known as the Oregon white truffle. Truffle authority James Trappe initially intended to name the species as a variety of T. gibbosum (i.e., as Tuber gibbosum var. oregonense) before molecular analysis revealed that genetic differences warranted distinction at the species level.
Tuber oregonense is part of the gibbosum clade of the genus Tuber, which contains species that have "peculiar wall thickenings on hyphal tips emerging from the peridial surface at maturity."
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