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Suillus intermedius

[ Basidiomycota > Boletales > Suillaceae > Suillus . . . ]

by Michael Kuo

This eastern Suillus species is fond of red pines and eastern white pine, and can be identified by its yellowish, slimy cap; the blackening glandular dots on its stem; the orangish flesh inside the stem; and especially by the distinctive ring, which is at first bracelet-like and gelatinous but later collapses to create a dry, grayish zone on the upper stem. Many authors emphasize that the taste of the slime on the cap's surface is acidic or sour; you are welcome to experiment, but I doubt you will need to take this one for the team in order to correctly identify Suillus intermedius—and the taste, in my experience, is somewhat variable anyway.

Suillus acidus var. intermedius is a previous name. Suillus acidus Peck (1906) has a whiter cap. It may well be the same mushroom as Suillus intermedius—in which case Suillus acidus is the older name and should take precedence. The name Suillus intermedius may be officially invalid, due to a competing "Suillus intermedius," now known as Gyrodon intermedius.


Ecology: Mycorrhizal with red pine and eastern white pine; growing alone, scattered, or gregariously; summer and fall; northeastern North America, the northern Midwest, and the Appalachian Mountains. The illustrated and described collections are from Michigan, Kentucky, and Québec.

Cap: 3.5–12 cm; convex at first, becoming broadly convex; thickly slimy when fresh; bald or sparsely, innately, radially fibrillose under the gluten; golden yellow to yellowish when young, darkening to dull orangish brown or golden brown; margin at first inrolled and attached to a whitish partial veil.

Pore Surface: Pale yellow when young; darker, dull yellow at maturity; not bruising; 2–3 roundish to angular pores per mm; tubes to 8 mm deep.

Stem: 6–10 cm long; 5–13 mm thick; more or less equal; tough; whitish to yellowish below fine brown glandular dots that blacken with maturity; with age sometimes developing bright yellow areas near apex; when young with a thin, bracelet-like, gelatinous ring that dries out and flattens against the stem surface with maturity, appearing like a grayish zone; basal mycelium white.

Flesh: Whitish to pale yellow in the cap; darker yellow to orangish or rosy salmon in the stem; not staining on exposure, or sometimes staining pinkish.

Odor and Taste: Odor not distinctive; taste of the slime on the cap acidic or sour (or occasionally not distinctive).

Chemical Reactions: Ammonia negative to grayish or pinkish on cap surface; negative to purplish on flesh. KOH dark gray on cap surface; gray to bluish on flesh. Iron salts negative on cap surface and flesh.

Spore Print: Cinnamon brown.

Microscopic Features: Spores 7–10 x 2–4 µm; fusiform; smooth; hyaline to yellowish in KOH. Hymenial cystidia subfusiform; smooth; thin-walled; brown to brownish purple. Caulocystidia 60–100 x 5–7.5 µm; cylindric to subclavate or subutriform; smooth; thin-walled; brownish purple to yellow brown in KOH.

REFERENCES: (Smith & Thiers, 1964) Smith & Thiers, 1971. (Snell & Dick, 1970; Grund & Harrison, 1976; Smith, Smith & Weber, 1981; Phillips, 1991/2005; Both, 1993; Bessette, Roody & Bessette, 2000; Roody, 2003; McNeil, 2006; Kuo & Methven, 2014.) Herb. Kuo 09019510, 09030203, 09150702, 10051505.

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


Suillus intermedius

Suillus intermedius

Suillus intermedius

Suillus intermedius

Suillus intermedius
Spore print

Suillus intermedius

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Kuo, M. (2016, January). Suillus intermedius. Retrieved from the MushroomExpert.Com Web site: