Major Groups > Boletes > Caloboletus inedulis


Caloboletus inedulis

[ Basidiomycota > Boletales > Boletaceae > Caloboletus . . . ]

by Michael Kuo

This eastern bolete is a study in interesting colors: the pale cap, yellow pore surface, pinkish red stem, and white flesh form an attractive combination—accentuated by the indigo blue bruising of the pore surface and the sky blue staining of the exposed flesh. The taste of this species is bitter (hence the Latin species epithet). The stem of Caloboletus inedulis is usually described as reticulate, but in my collecting experience the extent of the reticulation is highly variable, ranging from fairly prominent over the upper one-third of the stem, to nonexistent. Additionally, the color of the cap, while usually pale, ranges from nearly white to pale brown or, more rarely, brown.

Several species, also bitter tasting, are similar in appearance. Caloboletus calopus is larger and has a darker cap, along with substantially larger spores; it is a European species, but the name is sometimes applied in North America. Boletus roseipes grows only with eastern hemlock and has an olive brown cap when young. Boletus rubripes is found west of the Rocky Mountains and has larger spores. Boletus glabellus lacks the bitter taste and has deep yellow flesh in the base of the stem. Finally, western North America's Boletus frustosus is a bit stockier, has consistent reticulation, and grows only under conifers.


Ecology: Mycorrhizal with hardwoods (especially oaks), or with eastern hemlock; usually growing gregariously; summer and fall; widely distributed in North America east of the Great Plains; also documented from Central America. The illustrated and described collections are from Illinois and Indiana.

Cap: 4–13 cm; convex, becoming broadly convex; dry; when young finely velvety or kid-leathery to the touch, becoming bald and usually cracking up with age so that whitish flesh shows through the cracks; margin inrolled, with a 1–2 mm overhanging sterile portion; whitish to pale tan or brown.

Pore Surface: Dull yellow at first, becoming olive and eventually pale olive brown; bruising blue promptly; 2–4 angular pores per mm at maturity; tubes 10–15 mm deep.

Stem: 4–9 cm long; 1–2 cm thick; equal above a slightly swollen base; ground color whitish or yellowish to brownish (often paler toward apex), but sometimes developing pink to red streaks; sometimes finely reticulate over the upper portion with a pink to red reticulum, but often without reticulation—or with small, red, scaber-like dots; basal mycelium white.

Flesh: Whitish; soft; staining pale blue on exposure; purple-red in the stem.

Odor and Taste: Odor not distinctive; taste bitter.

Chemical Reactions: Ammonia negative on cap surface and flesh. KOH on cap surface negative to pale orange; on flesh orangish. Iron salts gray to blue-gray on cap surface; negative on flesh.

Spore Print: Olive brown.

Microscopic Features: Spores 9–15 x 3–5 µm; boletoid-fusiform; smooth; yellowish in KOH. Basidia 4-sterigmate. Hymenial cystidia 20–30 x 4–6 µm; lageniform to fusiform; smooth; thin-walled; hyaline in KOH. Pileipellis a cutis; elements 4–10 µm wide, smooth or encrusted, hyaline to yellowish- or brownish-walled in KOH. Contextual hyphae hyaline to yellowish in Melzer's reagent; inamyloid.

REFERENCES: (Murrill, 1938) Vizzini, 2014. (Singer, 1947; Snell & Dick, 1970; Smith & Thiers, 1971; Smith, Smith & Weber, 1981; Phillips, 1991/2005; Both, 1993; Bessette, Roody & Bessette, 2000; McNeil, 2006; Ortiz-Santana et al., 2007; Binion et al., 2008; Kuo & Methven, 2014; Zhao et al., 2014; Baroni, 2017; Zhang et al., 2017; Sturgeon, 2018; Kuo & Ortiz-Santana, 2020.) Herb. Kuo 08309703, 08300208, 06300708, 06220802, 07031403, 07201603, 07292002.

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Caloboletus inedulis

Caloboletus inedulis

Caloboletus inedulis

Caloboletus inedulis

Caloboletus inedulis

Caloboletus inedulis
Ammonia, KOH, iron salts

Caloboletus inedulis

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Kuo, M. (2020, August). Caloboletus inedulis. Retrieved from the MushroomExpert.Com Web site: