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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 µ; fusiform; smooth; hyaline to yellowish in KOH. Hymenial cystidia subfusiform; smooth; thin-walled; brown to brownish purple. Caulocystidia 60-100 x 5-7.5 µ; 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.

Further Online Information:

Suillus intermedius in Smith & Thiers, 1971
Suillus intermedius at Roger's 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: