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

Summary:
The Pacific Northwest status of boletes resembling Caloboletus calopus is not clear - some collections labeled as that species could be Caloboletus rubripes. Features of Caloboletus calopus include brown cap, yellow pores, a reticulated stem that is yellow to red, flesh and pores that turn rapidly blue when damaged, and bitter taste. |Caloboletus frustosus (Snell & E.A. Dick) D. Arora & J.L. Frank [also known as Boletus calopus var. frustosus] is said by Bessette(3) to have "a conspicuously rimose-areolate to fissured yellowish brown to grayish brown pileus at maturity" to which Boletus calopus var. calopus is "almost identical but has a nearly smooth pileus that does not become conspicuously rimose-areolate to fissured at maturity". The Bessette(3) description of the cap context says "unchanging when exposed" for var. frustosus and "rapidly staining when cut" for var. calopus, and the spore measurements given are different as well. But according to Siegel(2), based on preliminary genetic analysis, it is possible that Caloboletus frustosus is the same species as Caloboletus conifericola - if so the name Caloboletus frustosus would take precedence.

Caloboletus calopus var. calopus is said to be fairly common in the Pacific Northwest, and also occurs in MI, NH, and NY, (Bessette as Boletus calopus var. calopus). There are collections at the University of Washington labeled as Boletus calopus (variety not specified) from Washington and Oregon. There is a collection from BC as Boletus calopus at the University of British Columbia. Caloboletus frustosus is said to be fairly common from the Rocky Mountains of Idaho west to Washington and south to California, (Bessette as Boletus calopus var. frustosus). There is also a 1942 collection from Oregon as Boletus frustosus at the University of Washington.

Cap:
6-20cm, obtuse becoming convex to broadly convex, margin incurved at first, often with narrow band of sterile tissue; "olive-brown to gray-brown at first, becoming paler olive-brown to dark yellow-brown in age"; dry, somewhat tomentose when young, becoming nearly smooth when mature, usually rimose-areolate [cracked like dried mud] over disc when old, (Bessette), 10-30cm, convex to flat or irregular; dull brown to olive-brown, grayish brown, or olive-buff, sometimes yellow-brown or when old darker brown; "dry, dull, smooth to minutely hairy or fibrillose", often areolate [cracked like dried mud] when old, (Arora), dull buffy tan to olive-brown or yellow-brown, (Phillips)

Flesh:
"whitish to pale yellow, rapidly staining blue when cut", (Bessette), very thick; "pale yellow or whitish, quickly blueing when exposed", (Arora)

Pores:
1-2 per mm, round, becoming angular when mature; pale yellow at first, becoming olive-yellow when mature, rapidly turning blue when bruised; tubes up to 2cm long, often depressed near stem when old, (Bessette), pale yellow becoming darker or dingier yellow when old, typically bruising blue or blue-green quickly; tubes similar, (Arora)

Stem:
7-15cm x 2-5cm, nearly equal or widening downward, solid; "carmine-red to nearly scarlet, typically dark brownish toward the base and yellowish toward the apex", dry, conspicuously reticulate [netted] at least over upper part, the reticulation whitish to pinkish, (Bessette), 6-15(20)cm x 3-7cm, equal or bulbous, solid, firm; "yellow, but usually with pink to red zones or discolorations also present, or sometimes entirely reddish", turning blue when bruised; top or upper half finely reticulate, (Arora), yellow to slightly orange-yellow, reticulum whitish, base pinkish, (Phillips)

Chemical Reactions:
flesh stains yellow-brown with application of KOH and olive-green with FeSO4 (Bessette)

Odor:
somewhat pungent or not distinctive (Bessette)

Taste:
bitter (Bessette), distinctly and persistently bitter (Arora)

Microscopic:
spores 13-19 x 5-6 microns, elliptic, smooth, yellowish; conspicuous amyloid septa are found in cap trama and hymenophoral trama, (Bessette), spores 13-19 x 4-6 microns, spindle-shaped to elliptic, smooth, (Arora), spores 10.8-15.6 x 3.7-5.1 microns, fusiform-elliptic, smooth, yellowish, thick-walled, with droplets; basidia 4-spored, 33-48 x 10-13 microns, clavate, without basal clamp connection; cheilocystidia 35-50 x 7-12 microns, fusiform, pleurocystidia 50-80 x 8-10 microns, fusiform; cap cuticle a trichoderm of intertwined hyphae, some erect and exserted, 3-7 microns wide, with brownish pigmentation, septa without clamp connections; caulocystidia on the center of the stem 50-90 x 18-27 microns, fusiform to rostrate, thick-walled, (Breitenbach), spores 14-17 x 4-6 microns, elliptic to subfusoid, smooth, inamyloid, colorless to pale yellow in KOH, moderately thick-walled; basidia 4-spored, 30-45 x 10-13 microns, clavate; hymenial cystidia scattered, inconspicuous, 33-48 x 5-10 microns, narrowly fusoid-ventricose to cylindric, colorless, thin-walled; cap cuticle "a loosely interwoven trichodermium staining ochraceous in KOH with numerous free hyphal tips, often showing incrustations, hyphae 6-10 microns wide"; stem cuticle a layer of basidia and cystidia similar to hymenium, (Thiers for var. frustosus)

Spore Deposit:
olive brown (Bessette), dark olive-brown (Arora)