|Major Groups > Boletes > Red-Pored Boletes > Butyriboletus brunneus|
by Michael Kuo
Butyriboletus brunneus is a medium-sized to large bolete from eastern North America, featuring a thick, finely reticulate yellow stem that develops reddish stains and, often, a reddish zone at or just above the midpoint. The cap is brown, which helps separate it from the red-capped but otherwise similar Boletus speciosus. Butyriboletus brunneus is a dead ringer for the European Butyriboletus appendiculatus, and has gone under that name in some previous treatments.
I suspect there are at least two species currently going under the name "Butyriboletus brunneus": a weakly-bluing, oak-associated species (described and illustrated here) found in the oak-based hardwood forests of the Midwest, and a more strongly bluing, conifer- (especially eastern hemlock-) associated species with a more northern and northeastern range. If I am right, Boletus pseudopeckii, described from lower Michigan by Smith & Thiers (1971), may be the best name for the hardwood species.
Young specimens of Butyriboletus brunneus feature pores that appear "stuffed," resulting from the elongated cells that extend from the flesh in the spore-producing tubes (see the illustrations, lower right). Among the boletes only species of Butyriboletus and species centered around Boletus edulis share this feature—but in the edulis group, the tube mouths are white, rather than yellow. These two groups are not particularly closely related, however (see e.g. Kuo & Ortiz-Santana 2020), so the "stuffed pores" are an example of convergent evolution.
Boletus speciosus var. brunneus is a former name.
Ecology: Mycorrhizal with oaks and other hardwoods (but see the discussion above); usually growing alone or scattered, but sometimes growing gregariously; early summer through fall; widely distributed in eastern North America and the Midwest. The illustrated and described collections are from Illinois and Ohio.
Cap: 5–19 cm; convex, becoming broadly convex; dry; bald to the touch, but with a lens appearing finely, innately fibrillose; medium brown to yellow-brown, sometimes becoming orangish brown with age; the margin often overhanging slightly, especially when young.
Pore Surface: When young bright yellow with pores appearing "stuffed"; maturing to olive yellow; bruising slowly rusty brown; with 2–3 circular pores per mm at maturity; tubes to 15 mm deep, sometimes faintly bluish when sliced.
Stem: 5–12 cm long; 2–4 cm thick; equal; finely reticulate with a yellow to pale red reticulum over the upper portion or overall; pale yellow, developing red stains over the bottom half and, frequently, a red zone at or above the midpoint; sometimes bluing faintly where handled; basal mycelium pale yellow.
Flesh: Pale yellow or whitish; unchanging when sliced, or turning very slightly pale blue over the tubes.
Odor and Taste: Not distinctive.
Chemical Reactions: Ammonia pink to red on cap surface; greenish to bluish on flesh. KOH reddish or dull orange on cap surface; orangish on flesh. Iron salts greenish on cap surface; gray to bluish gray on flesh.
Spore Print: Olive brown.
Microscopic Features: Spores 11–14 x 3–4 µm; boletoid-fusiform; smooth; dull yellow in KOH. Basidia 4-sterigmate. Hyphal ends on tube mouths of young specimens ("cheilocystidia") to 75 x 5 µm; cylindric with rounded apices; smooth; hyaline to yellowish in KOH. Pleurocystidia infrequent; 26–35 x 4–7.5 µm; fusiform or narrowly lageniform; smooth; thin-walled; hyaline in KOH. Pileipellis a collapsing trichoderm; elements 2.5–6 µm wide, smooth or a little encrusted, hyaline in KOH (golden en masse); terminal cells cylindric with rounded apices.
REFERENCES: (Peck, 1890) D. Arora & J. L. Frank, 2014. (Smith & Thiers, 1971; Both, 1993; Bessette et al., 2000; Roody, 2003; McNeil, 2006; Šutara, 2014; Zhao et al., 2015; Bessette et al., 2016; Janda et al., 2019.) Herb. Kuo 08240508, 06071001, 09091208, 06281402; 07161602; 07191604.
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Cite this page as:
Kuo, M. (2020, November). Butyriboletus brunneus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/butyriboletus_brunneus.html