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

Summary:
Features include 1) light brown to warm brown, yellowish brown or reddish brown cap, 2) small white pores that become yellowish or olive yellow or brownish but do not turn blue, 3) massive stem with whitish reticulation (network), and 4) mild taste. It is a popular edible mushroom. Arora(2) described the often massive Boletus edulis var. grandedulis from CA, differing "in its brown to slightly reddish pore surface when mature". Var. edulis prefers Sitka spruce, whereas var. grandedulis occurs in a variety of coniferous forests, especially under pines, and occasionally live oak or madrone, (Siegel(2)).

Boletus edulis is widely distributed in North America, including at least BC (collections at the University of British Columbia), WA and CA (collections at the University of Washington), and OR (collections at Oregon State University). It has been reported from MT (Larry Evans, pers. comm.), and ID (K. Chadwick, pers. comm.). It occurs in Europe, Asia, North Africa, and Australia, (Breitenbach). Daniel Winkler has reported var. grandedulis from WA.

Cap:
4.5-38cm, convex to nearly flat; "brown to reddish brown, pale cinnamon brown, rusty red, or yellowish tan"; dry, viscid when moist, smooth to slightly wrinkled, (Bessette), 9-18cm, convex to obtusely convex becoming broadly convex to flat-convex, typically massive and heavy, margin incurved becoming downcurved; pale brown to buff, when old darkening to brown to reddish brown, often paler toward margin; moist to lubricous [slippery], usually becoming viscid to subviscid when wet or old, uneven or often irregularly pitted or wrinkled when old, (Thiers who includes B. pinophilus / B. rex-veris)

Flesh:
white, not turning blue when bruised, (Bessette), 2-4cm thick, firm, white, unchanging or darkening slightly when exposed, in stem white, unchanging except occasional brown stain at base, (Thiers who includes B. pinophilus / B. rex-veris)

Pores:
2-3 per mm, round; "white when young, becoming yellow to olive-yellow, then brownish yellow to brown in age, staining yellowish olive to dull orange-cinnamon or pale yellowish brown when bruised", tube layer 1-3cm thick, (Bessette), 2-3 per mm, angular, white becoming yellow when old, unchanging or staining brown when bruised, tube layer 1-3cm thick, adnexed becoming depressed when old, unchanging when exposed, (Thiers who includes B. pinophilus / B. rex-veris), pores in the Boletus edulis group are '' "stuffed" with a white material which disappears as the pores expand and the yellow pore surface is exposed'', (R. Bishop, pers. comm.)

Stem:
5-31cm x 2-7.5cm, widening downward or nearly equal, sometimes bulbous, stem solid; white or pale brown with distinct whitish reticulum [network] on upper one-third or more, (Bessette), 8-16cm x 1.5-2.5cm, massive, usually club-shaped, up to 6cm thick at bulbous base, solid; white to occasionally pale brown; dry to moist, bald but reticulate [netted] at least at top, (Thiers who includes B. pinophilus / B. rex-veris), reticulum first white then slightly darker than background (Lincoff(1))

Chemical Reactions:
cap stains orange with application of KOH, and slowly pale grayish green with FeSO4, flesh negative with KOH and pale grayish green with application of FeSO4, (Bessette)

Odor:
not distinctive (Bessette), pleasant (Phillips)

Taste:
not distinctive (Bessette), mild or nutty (Arora(1) who includes B. pinophilus / B. rex-veris), pleasant (Phillips), sweetish, like hazelnuts, (Lincoff(1))

Microscopic:
spores 13-19 x 4-6.5 microns, "elliptic, smooth, pale yellowish brown", (Bessette), spores 13-18 x 4-7 microns, fusiform [spindle-shaped] to somewhat elliptic, smooth, dark ochraceous in Melzer''s, colorless to pale ochraceous in KOH, walls slightly thickened; basidia 4-spored, 30-40 x 10-12 microns, clavate, colorless; hymenial cystidia often inconspicuous, often deeply embedded, 48-67 x 5-10 microns, "fusoid-ventricose, often narrowed and with tapered, elongated apices", colorless, thin-walled; cap cuticle a tangled trichodermium that collapses when old, occasional free hyphal tips; stem cuticle differentiated as a layer of fertile basidia with scattered to numerous fusoid-ventricose caulocystidia; clamp connections absent, (Thiers who includes B. pinophilus / B. rex-veris), spores (13)14-17(19) x 4-6.5 microns, subfusiform, smooth, as revived in Melzer''s reagent "ochraceous shaded greenish gray but gradually becoming ochraceous to weakly dextrinoid", in KOH pale tawny, wall only slightly thickened; basidia 4-spored, 32-40 x 10-12 microns, clavate, colorless in KOH; pleurocystidia "scattered, 42-48(65) X 7-10 microns, narrowly fusoid-ventricose", colorless in KOH, pale yellowish in Melzer''s reagent, smooth, thin-walled; cap cuticle a trichodermium of intertangled (and finally collapsing) hyphae 4-10 microns wide, colorless and gelatinous in KOH, lacking incrusting pigments; clamp connections absent, (Smith for var. edulis)

Spore Deposit:
olive brown (Bessette)