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Suillus granulatus

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

by Michael Kuo

Suillus granulatus is a well-known European species, associated with 2-needled pines like Scots pine. It features a sticky, orangish brown cap, and a non-bruising yellow pore surface that often exudes a milky liquid when the mushroom is young. The pores are not conspicuously wide and angular, and are not notably radially arranged. There is no ring on the stem, but there are glandular dots—at first pale and nearly invisible, darkening to dull brown with age.

In Europe, Suillus collinitus is the closest look-alike, but can be separated by its pinkish stem base and grainier cap surface. Suillus bovinus also appears with 2-needled pines in Europe, but is more brown all over, and features a radially arranged pore surface of large, angular pores.

The physical features characterizing Suillus granulatus also match Suillus weaverae, which is the North American mushroom probably featured in your field guide as "Suillus granulatus." However, Suillus weaverae is associated with 5-needled pines (primarily eastern white pine). The true Suillus granulatus does appear in North America, at least in Minnesota in association with red pine (Nguyen et al. 2016), probably as an imported species. The Minnesota collections studied by Nguyen and collaborators had been identified as "Suillus lactifluus," a species that was described by Smith & Thiers (1965) as a white-pine-associated deviation from Suillus granulatus featuring a sterile projecting cap margin, milky droplets on the young tubes, and non-darkening glandular dots. However, since Suillus lactifluus was described as a white-pine species it is probably best treated as a synonym of Suillus weaverae; meanwhile, determining the prevalence and range of North American Suillus granulatus awaits in-depth study of many well-documented collections (especially as to mycorrhizal host). At any rate, the white-pine-associated "Suillus granulatus" in North America is Suillus weaverae.


Ecology: Mycorrhizal with 2-needled pines, including Scots pine; growing alone or gregariously in woods or in urban locations near pines; summer through fall; originally described from Sweden by Linnaeus; widespread and common in Europe and in Asia; in north America apparently present, probably as an introduction, with red pine and possibly other 2-needled pines (see the discussion above). The illustrated and described collection is from Italy.

Note: A solitary, fairly young specimen is described.

Cap: 7 cm across; broadly convex; sticky; orangish brown with darker, reddish brown areas; bald; very finely rugged in a few places.

Pore Surface: Dull yellow; not bruising; pores small, slightly angular, about 2 per mm; tubes to about 5 mm deep.

Stem: 5 cm long; 1.5 cm thick; more or less equal; whitish to yellowish; with inconspicuous, concolorous glandular dots that blend in with the surface.

Flesh: Pale yellow in cap and upper stem; darker yellow in stem base; not changing when sliced.

Odor and Taste: Not distinctive.

Microscopic Features: Spores 8–10 x 2.5–3.5 µm; boletoid-fusiform to elongated-ellipsoid; smooth; hyaline to brown in KOH. Basidia about 35 x 7 µm; clavate; 4-sterigmate. Cystidia in bundles; 50–70 x 7.5–10; subfusiform to subclavate-flexuous; thin-walled; smooth; brown in KOH. Pileipellis an ixocutis. Clamp connections not found.

REFERENCES: (Linnaeus, 1753) H. F. A. de Roussel, 1806. (Phillips, 1981; Breitenbach & Kränzlin, 1991; Buczacki et al., 2013; Gminder & Böhning, 2017; Knudsen & Taylor, 2018; Noordeloos et al., 2018; Læssøe & Petersen, 2019; Kibby, 2020.) Herb. Kuo 10141403.

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Suillus granulatus

Suillus granulatus

Suillus granulatus

Suillus granulatus

Suillus granulatus

Suillus granulatus

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Kuo, M. (2022, February). Suillus granulatus. Retrieved from the MushroomExpert.Com Web site: