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

Summary:
Features include 1) almost bald cap that varies from reddish brown to cinnamon brown to yellow-brown to yellowish or buff, 2) dense flesh with mild taste, 3) yellow pores that usually bruise blue quickly, and 4) finely netted yellow stem.

This species has been confirmed only from CA where it occurs "in both the coastal region and in the Sierra Nevada foothills" (Arora(3)). It has been known as Boletus appendiculatus (Schaeff.) Secr. sensu Theirs. Arora(3) comment "Reports of Boletus appendiculatus sensu Thiers under conifers in the Pacific Northwest (e.g. Tylutki 1987) appear to be misidentifications based on Butyriboletus abieticola, Bu. primiregius and/or Bu. autumniregius. However, reports of Boletus appendiculatus with Q. garryana on Vancouver Island, British Columbia, are likely based on either this species and/or Bu. querciregius.", (Arora(3), with Latin names italicized). A collection from BC at the University of British Columbia as Boletus appendiculatus could be Butyriboletus persolidus or Butyriboletus querciregius.

Cap:
6-13cm, convex to spherical when young, becoming flat to flat-convex to shallowly depressed on disc, often highly irregular and uneven, margin incurved when young becoming broadly downcurved; buff to pale yellow when young, dull yellow to pale brown when older, often with stains or appearing overlaid with rust to red-colored blushes, occasionally with dark brown areas; dry to occasionally subviscid when wet, dull, bald to obscurely tomentose or velvety, sometimes shallowly cracked to areolate [cracked like dried mud] when old, (Thiers), 6-20cm, cushion-shaped to convex, becoming broadly convex to nearly flat when old, margin incurved at first and typically with narrow band of sterile tissue; "reddish brown to rusty brown or yellow-brown, sometimes pale to dull yellow, when young", dry, bald or nearly so, (Bessette), 6-20(30)cm, smooth or with a fine bloom when young, (Arora(1))

Flesh:
1-3cm thick, pale yellow to yellow, "unchanging or slowly changing to blue when exposed", in stem yellow near surface, whitish in center, unchanging or turning slightly blue in irregularly distributed areas when exposed, (Thiers), firm and dense; "pale yellow to yellow, not staining or slowly and erratically blueing when exposed", (Bessette), flesh in base usually pinkish or vinaceous (Arora(1))

Pores:
up to 1 mm broad, angular; yellow becoming dark yellow, turning blue when bruised; tube layer 1-2cm thick, deeply and broadly to narrowly depressed, (Thiers), 1-3 per mm, angular; pale yellow becoming yellow to dark yellow or olive-yellow, turning blue when bruised; tube layer 0.8-2cm thick, depressed near stem when old, (Bessette), usually turning blue when bruised, but sometimes not (especially in button stage), (Arora(1))

Stem:
6-9cm x 2-4cm, typically bulbous to wider in middle, sometimes equal, solid, occasionally with root-like prolongation; yellow, often with vinaceous to reddish brown stains, reticulation yellow or sometimes vinaceous to reddish; dry, reticulate [with a network] for two thirds of length, (Thiers), 5-14cm x 2-5cm, bulbous or wider in middle or sometimes equal, solid; yellow with reddish brown stains especially near base; dry, with a fine inconspicuous reticulation [network] on upper part, (Bessette), 5-15cm x 2-6cm, (Arora(1))

Chemical Reactions:
flesh pale vinaceous with KOH, (Thiers, Bessette)

Odor:
not distinctive (Thiers, Bessette)

Taste:
not distinctive (Thiers, Bessette)

Microscopic:
spores (10)12-14(16) x 4-5(6) microns, subfusoid [somewhat spindle-shaped] to subcylindric [somewhat cylindric], smooth, individual spores brown in Melzer''s, amyloid in mass, pale ochraceous in KOH, thin-walled; basidia 4-spored, 26-31 x 9-12 microns, clavate, colorless; hymenial cystidia 48-65 x 8-13 microns, fusoid-ventricose, colorless, thin-walled; cap cuticle differentiated as a trichodermium of interwoven to tangled hyphae, pale brown in KOH, not incrusted; stem cuticle fertile on ridges, interwoven in other parts; clamp connections absent, (Thiers), spores 12-16 x 4-6 microns, somewhat cylindric to somewhat fusoid, smooth, ochraceous, (Bessette), spores 12-15 x 3.5-5 microns (Arora(1))

Spore Deposit:
dark olive brown (Thiers), olive brown (Bessette)