E-Flora BC: Electronic Atlas of the Flora of British Columbia

Summary:
Features include 1) a spherical to irregular fruitbody with a surface that is whitish becoming lemon yellow, usually staining slowly yellow to orange or reddish brown on handling (reddish only when surface actually cut), 2) loose brown rhizomorphs that stand out distinctly on dried fruitbodies against the white to yellow surface, 3) a spore mass that is pallid becoming grayish olivaceous or olive, 4) growth under conifers, 5) smooth, oblong, inamyloid spores, 6) basidia that are mostly 6-spored and 8-spored, and 7) a peridium that is one-layered, composed of appressed hyphae with oleiferous hyphae and inflated cells that are not in groups. It is abundant among false truffles in the Pacific Northwest (Trappe(13)). This is one of three Rhizopogon species mentioned as common for the Pacific Northwest, with R. parksii and R. ellenae, (Ammirati).

Rhizopogon occidentalis is found in WA, OR, northern CA, and ID, (Trappe(13)). It is known from OR, ID, CA, (Smith(30) who examined collections also from WA but comments that at least one of them has spores about 9 x 3 microns and may be a large spored variety of the species). There is a Paul Kroeger collection from BC deposited at the University of British Columbia.

Outer Surface:
1-6cm across, whitish at first, near lemon yellow when mature, "surface staining yellow to orange or reddish-brown slowly on handling", staining red when cut, and "as dried covered with brown rhizomorphs", (Smith(4)), 1-5cm across, "irregularly potato-shaped or pear-shaped; whitish at first, then lemon yellow in age, bruising orange or reddish brown; minutely hairy with loose cordlike brownish rhizomorphs", (Phillips), 1.3-8cm across, "white when young, becoming bright yellow with greenish tint, often developing some brownish to reddish areas but not rapidly staining when injured or cut"; "coated with small fibrils and more conspicuous buff to brownish or reddish brown chord-like strands", (Ammirati), 1-6cm across, spherical to irregular, ovoid, pear-shaped, etc.; surface color "whitish at first, slowly becoming yellow (finally nearly lemon-yellow)", "staining yellow to orange or reddish brown slowly on handling", (not all collections showing this change readily), staining red when cut, when dried the retaining the color of the fresh surface (whitish to pale lemon-yellow); "dry and fibrillose beneath a conspicuous coating of buff to tawny-brown rhizomorphs, and these standing out distinctly on the dried specimens", "the rhizomorph layer drying to a cinnamon-tan"; (Smith(30)), "yellowish white to yellow, often with orange to red areas, with yellow to orange rhizomorphs appressed to form a network over the entire surface, sometimes reddening slightly where bruised or cut", (Trappe, M.(3))

Chemical Reactions:
FeSO4 on dried peridium olive (Smith(30)), KOH on peridium lilac to red (for this group in key) (Smith(4))

Interior:
olive drying cinnamon buff, (Smith(4)), minutely chambered; pale yellow-orange, drying cinnamon buff, (Phillips), firm; pallid to pale greenish gray, (Ammirati), consistency "when dried rather brittle and crumbly"; "pallid becoming grayish olivaceous to olive and drying to a cinnamon-buff"; chambers large, in older specimens 0.05-0.01cm, (Smith(30)), white to gray or yellow, becoming some shade of olive or brown; at maturity dry or somewhat powdery, (Trudell), "white to gray to pale tan to olive to brown, depending on level of maturity", (Trappe, M.(3))

Odor:
none or slight (Smith(30)), sourdough (Phillips)

Taste:
sweetish (Arora)

Microscopic:
spores 5.5-7 x (2)2.3-2.6(3) microns, "peridium one-layered, of appressed hyphae 3-8 microns wide, oleiferous hyphae present, also inflated hyphal cells 10-20 microns but not in groups", (Smith(4)), spores 5.5-7 x 2.3-2.6 microns, elliptic, smooth, (Phillips), 5.5-7 x (2)2.3-2.6(3) microns, oblong, smooth, in Melzer''s reagent yellowish singly, yellowish tan in groups, in KOH yellowish to colorless singly and deeper ochraceous to dingy cinnamon-buff in masses, often with 2 oil drops; basidia mostly 6-spored and 8-spored, 14-20 x 7-9 microns, clavate, colorless, thin-walled; paraphyses "like the basidioles but in age developing thickened walls but central body not dextrinoid"; subhymenium "more or less cellular and 1-3 cells deep, not gelatinous in KOH"; tramal plates composed of hyphae 2.5-6 microns wide, interwoven, colorless, smooth, finally gelatinous-refractive; peridium "one-layered, of appressed hyphae 3-8 microns broad, if the rhizomorph-layer is included the content and/or walls are both more or less cinnamon, beneath this the hyphae with yellow to hyaline walls (revived in KOH)", (revived peridium essentially clean in subcutis but near surface there may be more amorphous debris); oleiferous hyphae present as well as enlarged hyphal cells in some of the fundamental hyphae (10-20 microns in diameter); all tissues inamyloid; clamp connections absent, (Smith(30)), spores "smooth, thin-walled, and often elongated to spindle-shaped", (Trudell)