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Summary: Features include 1) blackish to dark olive-brown cap with a powdery bloom, the cap often reddening somewhat, dry and often wrinkled and velvety, often becoming areolate [cracked like dried mud] when old, 2) white to pale yellow flesh that sometimes turns blue, 3) large irregular yellow pores that sometimes turn blue, 4) striate stem that is yellow to tan with red granules at first and becomes dark red in upper part or throughout, 5) growth on the ground or on wood, and 6) microscopic characters. Boletus zelleri is common in Pacific Northwest south through CA and into Mexico, (Bessette), occurs in BC, WA, and OR (Snell), and has been reported from ID (Drew Parker pers. comm.).
Cap: 5-10cm, convex becoming broadly convex to flat; "dull black to dark gray to blackish brown, fading to dark brown or dark olive-brown in age, margin often reddish tinged"; "dry, covered with a white bloom and wrinkled when young", becoming subtomentose [somewhat tomentose] to smooth when mature, occasionally slightly areolate [cracked like dried mud] when old, with yellow or red tints showing in the cracks, (Bessette), 5-10cm, convex, becoming convex to flat when old; black to blackish brown, sometimes fading to dark brown, often with a reddish margin; dry, conspicuously white-pruinose when young, becoming bald to obscurely tomentose to tomentose when old, rugulose [finely wrinkled] to verrucose [warty] when young, more or less smooth at maturity, not conspicuously areolate [cracked like dried mud] when young, but sometimes becoming so when old, (Thiers), 3-16cm, "black to dark gray or dark olive-brown when fresh", often reddening somewhat when old or in wet weather, especially toward margin, (Arora), smooth or quite wrinkled, often velvety, (Phillips)
Flesh: white to pale yellow, not changing, or sometimes turning blue when exposed, (Bessette), up to 1.5cm thick; "whitish to pale yellow, unchanging or becoming blue when exposed"; in stem yellow when young and typically red when older, sometimes turning blue in irregular areas when exposed, (Thiers)
Pores: 1-2 mm wide when mature, irregular; olive-yellow, becoming dark yellow when mature, "typically staining blue when bruised"; tube layer 0.8-1.5cm thick, often depressed around stem when old, (Bessette), typically more than 1mm wide, highly irregular in outline, olive-yellow when young, changing to dark yellow when old, becoming blue when bruised; tube layer up to 1.5cm thick, colored as pores, becoming blue when bruised or exposed, (Thiers), yellow to dark yellow or olive-yellow, often turning blue when bruised, but often not turning blue, (Arora)
Stem: 5-8cm x 0.7-1.3cm, nearly equal, solid; "densely punctate with red to brownish red dots and points over a yellow ground color"; dry, longitudinally striate; "base coated with white to pale yellow mycelium; partial veil and annulus absent", (Bessette), 5-8cm x 0.7-1.3cm at top, equal or occasionally widening slightly from top, solid; tan when young, becoming more or less obscured with red granules, sometimes red at top, becoming yellowish with red punctae toward base, old stems often red; dry, granulose to punctate, especially toward base, with white to pale yellow mycelium at base, (Thiers), 4-12cm x 0.5-3(5)cm, equal or slightly thicker at either end; "yellow to tan with delicate red granules when young", usually dark red in upper part or throughout when old, (Arora)
Chemical Reactions: flesh stains greenish with application of NH4OH, (Bessette)
Odor: not distinctive (Bessette)
Taste: not distinctive (Bessette), slightly acidic (Lincoff(1))
Microscopic: spores 12-15 x 4-6 microns, subelliptic [somewhat elliptic] to subventricose [somewhat wider in middle], smooth, yellow, (Bessette), spores 12-15 x 4-5.5 microns, (occasional spore up to 24 microns), subelliptic to subventricose, smooth, pale yellow to pale ochraceous in KOH, ochraceous tawny in Melzer's reagent; basidia 4-spored, rarely 1-spored or 3-spored, 18-21 x 10-11 microns, clavate, colorless; hymenial cystidia rare to scattered to numerous, lacking in some fruitbodies, 40-85 x 10-13 microns, "clavate to obtusely fusoid to fusoid-ventricose to obscurely mucronate", colorless to rarely yellowish in KOH, thin-walled; cap cuticle "a trichodermium of free, septate, erect, inflated hyphal tips, often appearing similar to pileocystidia", the subterminal cell spherical to pear-shaped and the terminal cell somewhat pyramidal in outline, walls of cuticular hyphae often incrusted but not in spiral fashion, hyphae typically collapsing and appearing as a tangled mass of hyphal tips in older caps, appearing repent to interwoven (in B. chrysenteron, terminal hyphal cells are more or less equal in size and the hyphae are interwoven or more or less radially arranged, as well as being heavily spirally incrusted); stem cuticle interwoven, heavily incrusted, with laticiferous hyphae throughout; clamp connections absent, (Thiers), spores 12-16 x 4-5.5 microns, spindle-shaped to elliptic, (Arora)
Spore Deposit: olive brown (Bessette, Thiers)
Habitat / Range
single, scattered, or in groups on ground or decaying wood in mixed conifer forest, (Bessette), late summer and fall (Miller), most prevalent in fall, but found at other times as well, (Trudell), spring, summer, fall, winter
Boletus chrysenteron has paler brown cap that becomes conspicuously areolate [cracked like dried mud] when old, with reddish flesh showing in the cracks, (Bessette). In deciding macroscopically between Boletus zelleri and B. chrysenteron / B. truncatus, a very dark pruinose cap means B. zelleri; a very areolate cap [with cracks like dried mud] with red in the cracks means B. chrysenteron or B. truncatus, but microscopic examination of the spores and cap cuticle is often necessary to distinguish B. truncatus and B. chrysenteron respectively from B. zelleri.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2020. E-Flora BC:
Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for
Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2021-04-12 12:02:17 PM
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