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Gyroporus borealis

by Michael Kuo, 13 June 2026

This North American bolete, like all species of Gyroporus, features a brittle, hollowing stem and a yellow spore print; it can putatively be separated from other North American gyroporuses on the basis of its colors (orangish brown to brown), spore dimensions (8–12 x 5–6.5 µm), and distribution (northeastern North America, with human-introduced populations in the Pacific Northwest).

The scientific support for this species is, well . . . I will be charitable and say "minimal." I think "Gyroporus borealis" should be treated as Gyroporus castaneus; see the discussion on the page for Gyroporus. But the collections described and illustrated on this page meet the color and range criteria for borealis; they are from Minnesota and Appalachian Pennsylvania and Ohio, and have orange-brown caps and stems. The spores of these collections are too small to match borealis, but as I argue in the linked discussion the spore dimension distinctions offered in the literature are dubious. Actually, the color and distribution differences are also dubious, but hey, mushrooms can't read, so there it is.

Description:

Ecology: Mycorrhizal with precise hosts uncertain; growing alone, scattered, or gregariously on the ground, especially in disturbed-ground locations like path sides, embankments, and so on; summer and fall; originally described from Vermont (Davoodian et al. 2020), with paratype collections collections from Ohio and Washington; putatively distributed in "northeastern" and "northwestern North America," but in the northwest only with eastern North American trees used for landscaping. The illustrated and described collections are from Minnesota, Ohio, and Pennsylvania.

Cap: 2.5–6 cm; convex, becoming broadly convex or nearly flat in age; dry; bald or, when young, slightly velvety; sometimes becoming somewhat wrinkled; brown to yellow-brown, orangish brown, or reddish brown; the margin often splitting in places with maturity.

Pore Surface: Whitish at first, becoming pale yellow; not bruising, or bruising slowly brownish; 2–3 circular to angular pores per mm; tubes to 8 mm deep.

Stem: 2.5–5 cm long; 0.5–1 cm thick; more or less equal, or enlarged toward the base; dry; brittle; hollowing; colored like the cap; not bruising; not reticulate; basal mycelium white to pale pastel orange.

Flesh: White; not staining on exposure.

Odor and Taste: Not distinctive.

Spore Print: Yellow.

Microscopic Features: Spores 6–9 x 3.5–5 µm (see note above); ellipsoid; smooth; hyaline to yellowish in KOH. Basidia 25–32 x 5–8 µm; clavate; 4-sterigmate. Hymenial cystidia scattered and inconspicuous; to 35 x 5 µm; narrowly lageniform; smooth; thin-walled; hyaline in KOH. Pileipellis a trichoderm; elements 6–14 µm wide, smooth, septate, hyaline to dull golden or brownish in KOH; terminal cells cylindric with rounded apices, or narrowly lageniform, cystidioid; subterminal cells not swollen, or occasionally slightly enlarged.

REFERENCES: N. Davoodian, O. Asher, W. J. Sturgeon, J. F. Ammirati & T. P. Delaney, 2020. (Davoodian et al., 2018; Davoodian et al., 2020. Based on descriptions and photos, the following North American treatments of G. castaneus may represent G. borealis, at least in part: Coker & Beers, 1943; Singer, 1945; Snell & Dick, 1970; Smith & Thiers, 1971; Smith, 1973; Grund & Harrison, 1976; Smith, Smith & Weber, 1981; Phillips, 1991/2005; Both 1993; Roody, 2003; Bessette, Roody & Bessette, 2006; McNeil, 2006; Miller & Miller, 2006; Trudell & Ammirati, 2009; Baroni, 2017; Sturgeon, 2018; McKnight et al., 2021.) Herb. Kuo 07079403, 07180201, 07162501.

This website contains no information about the edibility or toxicity of mushrooms.

Ammonia, KOH, iron salts

Spores and pileipellis

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Cite this page as:

Kuo, M. (2026, June). Gyroporus borealis. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/gyroporus_borealis.html