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

Summary:
Features of this common bolete include 1) plush maroon brown cap, 2) stem of similar color, often with roughened longitudinal ridges reminiscent of bark, sometimes netted near the top, 3) yellow pores that do not stain blue, and 4) growth on or near rotting conifers. A whitish then yellow stage of the pyrenomycete Hypomyces chrysospermum frequently grows on it. The Aureoboletus name was proposed in Halling(6) in 2015 and supported in 2020 by the molecular study of Kuo(12).

'Boletus'' mirabilis is common in WA and OR and also found in northern CA, (Thiers), ID (Drew Parker, pers. comm.), MT (Larry Evans, pers. comm.), and MI (Arora). It is also common in BC and there are collections at the University of British Columbia.

Cap:
5-15(20)cm, convex to flat, margin often hung with fragments of tissue; dark reddish brown to maroon-brown, bay-brown, or chocolate-brown; moist to dry, granular to plush-like (with small often erect fibrillose scales), (Arora), 7-15cm, convex to bluntly convex becoming broadly convex to flat-convex, margin often with hanging remnants; dark reddish brown; "moist to lubricous when young, dry when older, somewhat appressed fibrillose-scaly to rough-tomentose when young, becoming conspicuously fibrillose-scaly and often squarrose-scaly with age", sometimes granular-scaly to somewhat areolate [cracked like dried mud] or cracked-scaly, (Thiers)

Flesh:
thick; "white to dingy pinkish or yellow, rarely blueing when bruised", (Arora), 1-2cm thick, white to yellow, frequently with numerous areas staining flesh-colored when older, rarely changing to blue in irregular areas, in stem pale vinaceous, sometimes appearing yellow and typically becoming yellow when dry, (Thiers)

Pores:
1-2 mm wide, pale yellow becoming mustard yellow and finally greenish yellow, sometimes staining darker yellow when bruised; tubes yellow, (Arora), 1-2 mm wide, round to angular; yellow becoming olive yellow when old, unchanging or becoming deeper yellow when bruised; tube layer 1-2.5cm thick, depressed around stem, colored as pores, unchanging when bruised, (Thiers)

Stem:
7-20cm x 1-3.5cm, usually club-shaped, firm; dark brown to maroon-brown or reddish brown, "sometimes with yellow, buff, or beige streaks"; "often roughened, pitted, or longitudinally ridged", the top often coarsely reticulate [netted], the base often with yellow mycelium, (Arora), 8-15cm x 1-3cm, club-shaped, up to 5cm wide at base, solid; dark brown with occasional streaks of ivory or beige or brown; moist to dry, bald, but typically shaggy reticulate at top, "becoming smooth to uneven or ridged or shallowly pitted toward base, sometimes roughened and split with age", with yellow mycelium at base, (Thiers), partial veil and annulus absent (Bessette)

Odor:
acid or mild (Thiers), pleasant (Phillips)

Taste:
not distinctive (Thiers), pleasant (Phillips)

Microscopic:
spores 18-24 x 7-9 microns, spindle-shaped to elliptic, smooth, (Arora), spores 18-22 x 7-9 microns, subfusoid to subelliptic, smooth, dark brown in Melzer''s, ochraceous in KOH, thick-walled; basidia 4-spored, 31-36 x 7-11 microns, clavate, colorless; hymenial cystidia scattered to numerous, 60-90 x 10-18 microns, fusoid-ventricose with obtuse to elongated apices, colorless, thin-walled; clamp connections absent, (Thiers)

Spore Deposit:
olive brown (Arora, Thiers)