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

Summary:
Features include 1) a nearly black cap with a whitish bloom and a smooth or somewhat pitted surface, 2) white to vinaceous-tinged, unchanging flesh, 3) small angular pores that are white becoming yellowish and do not turn blue, 4) club-shaped to equal, reticulate stem that is white and may become vinaceous brown, 5) growth under hardwoods or conifers, and 6) microscopic characters. Boletus regineus was known for many years on the west coast of North America as Boletus aereus Bull. The taxon of CA, OR, and WA was redescribed in 2008 as Boletus regineus D. Arora and Simonini. The authors noted that the gelatinized pileipellis clearly distinguished it from European B. aereus, which has a dry, velvety cap cuticle with a non-gelatinized trichoderm of subparallel hyphae, and a browner stem, (Arora(2)). Boletus mottiae Thiers, California Mushrooms p.36. 1975 is said to be a "mutated" collection of Boletus regineus.

Collections of Boletus regineus were examined from CA where it is fairly common, but distribution in OR and WA is also mentioned (Arora(2)). It has been reported as Boletus aereus from OR (H. Thiers 1986, pers. comm. to L. Norvell, Dick Bishop pers. comm.), WA (J. Lindgren pers. comm., M. Beug pers. comm., collection at the University of Washington as B. aereus), and BC (O. Ceska pers. comm.). A collection from OR was used in Arora(3).

Cap:
7-30cm across, convex becoming broadly convex to nearly flat; "very dark brown when fresh but often entirely or partially overlaid with a fine white bloom that gives it a paler, frosted appearance, in age the hoary patches tending to disappear and the surface often becoming paler brown or cinnamon blotched with even paler (white to pale tan) areas"; bald except for the hoary patches, moist but typically viscid when old or in wet weather, "sometimes uneven or with broad depressions", (Arora(2)), 5-15(20)cm, convex becoming broadly convex to flat; "dark brown to nearly black when young and covered at least partially with a fine whitish bloom", but when old becoming smooth and cinnamon or red-brown or blotched with paler, whitish to tan areas; dry or moist (or viscid only when old), smooth or somewhat pitted, (Arora(1)), 10-15cm, convex to nearly spherical when young, becoming broadly convex to flat-convex to flat when old; dark brown to almost black, when old sometimes fading irregularly on disc to buff or reddish brown with irregular areas almost white to tan; moist, never viscid, often pitted or with broad depressions, especially toward margin, bald but with scattered white pruinose areas or patches, (Thiers)

Flesh:
thick and white in cap and stem, "but sometimes vinaceous-tinged when young", "not staining appreciably when cut or sometimes exhibiting a very slight blueing just above the tube layer", (Arora(2)), thick; white or tinged reddish, not turning blue when exposed, or turning blue only slightly near tubes, (Arora(1)), 2-4cm thick, vinaceous when young, white when old except pale yellow above tubes and pale vinaceous below cap surface; in stem white and unchanging when exposed, (Thiers)

Pores:
pores and tubes white when young becoming yellow then greenish yellow as fruiting body matures, not turning blue when bruised, (Arora(2)), at first stuffed with pith; white when young, becoming yellow to greenish yellow when old, not turning blue when exposed, (Arora(1)), up to 1mm, angular; white when young, becoming yellow when mature, not changing where bruised; tube layer 1.5-2cm thick, adnate to adnexed, becoming depressed, white when young, becoming yellow when mature, (Thiers), 1-3 per mm, angular; white becoming dingy yellow; tube layer 1-2cm thick, becoming depressed near stem when old, (Bessette)

Stem:
7-20cm x 2.5-8cm, equal to clavate [club-shaped] or slightly bulbous (especially when young); white or nearly so, sometimes brownish when old but more often remaining white; bald except for reticulation over at least the upper part, the reticulation white at first, white to brown when old, (Arora(2)), 5-15cm x 2-5cm at top, usually widening downward when young but often equal when old, firm, solid; white or often brown when old; "finely reticulate at least over upper part", (Arora(1)), 8-11.5cm x 2.5-4cm at top, clavate [club-shaped] to subbulbous [somewhat bulbous] when young, unchanging or becoming more or less equal when old, solid; when young pallid to almost white, unchanging or becoming vinaceous or vinaceous brown when old; "dry, reticulate at least over upper half, sometimes strongly and conspicuously so", (Thiers)

Chemical Reactions:
flesh does not stain with application of KOH or FeSO4, (Bessette)

Odor:
mild (Arora(2)), mild (Thiers)

Taste:
mild (Arora(2)), mild or pleasant (Arora(1)), mild (Thiers)

Microscopic:
spores (11.5)12-15(17) x (3.9)4-4.7(5.4) microns, "variable in shape and dimensions, long ellipsoid-fusiform"; basidia clavate, colorless, mostly 4-spored, 23-40 x 8-11.5 microns; hymenial cystidia thin-walled, inconspicuous; cap cuticle "a completely gelatinized cutis when mature (and sometimes even in youth)", typically 200-250 microns thick, cuticular cells 7-10 microns wide, "variable in shape, sometimes branched or with diverticula", (Arora(2)), spores 12-14 x 4-5 microns, spindle-shaped to elliptic, smooth, (Arora(1)), spores 12-13.5 x 4-5 microns, subelliptic to subfusoid, smooth, pale ochraceous in KOH and Melzer''s, thin-walled; basidia 4-spored, 23-30 x 8-10 microns, colorless in KOH; hymenial cystidia inconspicuous, embedded in hymenium, 28-34 x 7-11 microns, colorless in KOH and Melzer''s, thin-walled; cap cuticle "a broad (175 microns) trichodermium of erect, septate hyphal tips, terminal cells not enlarged, not incrusted, hyaline in KOH, pale ochraceous in Melzer''s, hyphae 4-5 microns wide"; clamp connections absent, (Thiers)

Spore Deposit:
"olive-brown in mass, but yellower than closely related species under the microscope", (Arora(2)), dark olive-brown (Arora(1), Thiers)