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

Summary:
Features include a pale buff to tan cap, yellow flesh and pores that turn blue on exposure, a smooth stem that when young is yellow at the top and red at the base but when old is typically dark red throughout, and a usually bitter taste.

Caloboletus rubripes is found in the Pacific Northwest, Southwest, and Mexico, and is especially common in NM and CO, (Bessette). It is specifically found in WA and OR (collections at the University of Washington), and is recorded also from ID and CA, (Michelle Seidl, pers. comm.). It has been reported from MT (Larry Evans, pers. comm.), A Paul Kroeger collection from BC is deposited at University of British Columbia.

Cap:
6-15(25)cm, convex, sometimes becoming flat; "pale buff to olive-buff to tan"; dry, dull, smooth or velvety, often cracked or furrowed when old, (Arora), 4-18cm, convex to cushion-shaped, expanding, margin incurved to inrolled for a long time, even; "buff to olive-buff to olive-brown, staining brown when bruised"; "dry, velvety-tomentose to appressed-fibrillose", often cracked-areolate when old, (Bessette), pale buff to dull tawny brown, darker where handled (Phillips), when young pale buff, unchanging or becoming pale brown when old, sometimes fading to buff on the margin, typically staining brown when bruised or handled, (Thiers)

Flesh:
thick, firm; "buff to pale yellow or even whitish", but turning blue when exposed, (Arora), whitish to pale yellow, instantly turning blue when exposed, (Bessette), up to 3cm thick, buff to yellow, turning blue immediately on exposure; in stem yellow, dark red to almost black at base, turning blue when exposed, (Thiers), cream to yellow or rarely pinkish in cap, white to yellow in upper stem, and red to vinaceous in base; when cut, blueing instantly, (Trudell)

Pores:
pale yellow becoming darker or duller yellow when old, turning blue when bruised, (Arora), 1-3 per mm, angular, "yellow at first, becoming olive-yellow at maturity", instantly turning blue when bruised; tube layer 0.8-1.6cm thick, (Bessette), tube layer shallowly depressed when young, deeply depressed when old, (Thiers)

Stem:
7-13(20)cm x 1-4cm, sometimes swollen in lower part (especially when young), firm, solid; usually yellow at top with bright pink to reddish areas in lower part, becoming dark red throughout when old; not reticulate but often longitudinally striate when old, (Arora), 5-12cm x 2-4.5cm, nearly equal or widening or narrowing downward, solid; yellow near top and pinkish red to purple-red overall when old, quickly turning blue, then slowly staining grayish olive when bruised, mycelium whitish to pale yellow; dry, bald or sometimes longitudinally striate, lacking reticulation; partial veil and ring absent, (Bessette), yellow mycelium at base (Thiers)

Chemical Reactions:
flesh stains yellow-orange with application of KOH (Bessette)

Odor:
unpleasant or not distinctive (Bessette), often strong, unpleasant (Thiers)

Taste:
usually bitter (Arora), bitter (Bessette)

Microscopic:
spores 12.5-17.5 x 4-5 microns, spindle-shaped to elliptic, smooth, (Arora), spores 12-18 x 4-5 microns, subfusoid to subcylindric, smooth, ochraceous, (Bessette), spores 12.5-17.6 x 4-5 microns, subcylindric to subfusoid to narrowly subelliptic, smooth, ochraceous in KOH, dark ochraceous in Melzer''s, thin-walled; basidia 4-spored, 26-30 x 7-13 microns; hymenial cystidia scattered, 24-35 x 5-7 microns, embedded in hymenium, fusoid to occasionally clavate or fusoid-ventricose, colorless, thin-walled; cap cuticle a trichodermium of interwoven hyphae, occasionally incrusted; clamp connections absent, (Thiers)

Spore Deposit:
olive-brown (Arora, Bessette)