Suillus luteus

Description
Mushroom Identification
Look-Alikes
History
Side Effects
Video

Description

Suillus luteus is a medium to large bolete with a slimy, brown cap. Its short to stubby stalk has brown dots and a well-developed ring.

This common fungus native to Eurasia, from the British Isles to Korea, has been introduced widely elsewhere, including North and South America, southern Africa, Australia and New Zealand.

Edible, though not as highly regarded as other bolete mushrooms, and is commonly prepared and eaten in soups, stews or fried dishes. The slime coating, however, may cause indigestion if not removed before eating.

This mushroom grows in coniferous forests in its native range, and pine plantations in countries where it has become naturalized. It forms symbiotic ectomycorrhizal associations with living trees by enveloping the tree's underground roots with sheaths of fungal tissue. The fungus produces spore-bearing fruit bodies, often in large numbers, above ground in summer and autumn.

Unlike most other boletes, it bears a distinctive membranous ring that is tinged brown to violet on the underside.

Common names: Slippery Jack, Smörsopp (Sweden), Parastā sviestbeka (Latvia).

Mushroom Identification

Ecology

Mycorrhizal with various conifers; growing gregariously; late summer and fall--or in winter during warm spells; widely distributed in North America. In my area (central Illinois) Suillus luteus grows in both red pine and eastern white pine plantations. Curiously, in plantations where rows of both trees occur, it always seems to stick with one of the other species.
Cap

5-12 cm; convex when young, becoming broadly convex to flat; slimy; shiny when dry; partial veil tissue often hanging from the margin; dark brown to dark reddish-brown to yellow-brown; fading with age.
Pore Surface

Covered with a whitish partial veil when young; whitish to pale yellow, becoming yellow to olive-yellow with age; not bruising; pores under 1 mm across; tubes 4-15 mm deep.
Stem

3-8 cm long; 1-2.5 cm thick; equal; with glandular dots above the ring; whitish, yellowish towards apex; discoloring brown to purplish brown near the base in age; with a flaring white ring that develops purple shades on the underside and is often gelatinous in humid or wet weather.
Flesh

White to pale yellow; not staining on exposure.
Chemical Reactions

Cap surface gray with KOH or ammonia, grayish olive with iron salts; flesh bluish to olive with iron salts, pinkish, then pale bluish with KOH or ammonia; pore surface rusty red with ammonia, brownish with KOH or iron salts.
Spore Print

Brown.
Microscopic Features

Spores 7-9 x 2.5-3 µ; smooth; subfusoid.

Look-Alikes

Suillus collinitus

Similar colored fruitbodies however have no ring and show pinkish basal mycelium.
Suillus granulatus

Widely distributed and edible species occurring in the same habitat. Suillus granulatus is yellow-fleshed and exudes latex droplets when young, but most conspicuously bears neither a partial veil nor a ring.
Suillus grevillei

Found under larch and has a yellow cap, while immature fruit bodies of Gomphidius glutinosus may look comparable from above but have gills rather than pores underneath.
Suillus borealis

Have partial veils, but lacks the distinctive ring of S. luteus.

History

When in 1753 Carl Linnaeus described this bolete he called it Boletus luteus. Later, in 1888, Lucien Quélet moved it from the Boletus genus and named it Ixocomus luteus. The currently accepted scientific name of the Slippery Jack, Suillus luteus, dates from a 1796 publication by the French mycologist Henri François Anne de Roussel (1748 - 1812).

Synonyms of Suillus luteus include Boletus luteus L., and Ixocomus luteus (L.) Quél.

Suillus luteus is the type species of the Suillus genus.

The common name Slippery Jack is an obvious reference to the slimy nature of caps of this mushroom during wet weather - although they tend to become smooth and semi-matt and hence they are not particularly sticky during warm dry spells.

The specific epithet luteus seems obscure, because the Latin prefix lute- generally implies saffron yellow (the pores are yellow, but more lemon yellow than saffron); however, another meaning of luteus is dirty or muddy, and that may be the origin in this instance.

The generic name Suillus is much more straightforward, coming from the Latin noun sus, meaning pig. Suillus, therefore, means 'of pigs' (swine) and is a reference to the greasy nature of the caps of all fungi in this genus.

Side Effects

The Slippery Jack should be well washed as the slimy surface can collect debris and the surface of the cap should be peeled before eating. There are some reports of gastrointestinal discomfort which is attributed to the surface of the mushroom.

In Poland, Belarus and Sweden there were indications of mercury present in the dried mushrooms however, providing the fresh intake of slippery Jack does not exceed 300g per week, it is thought that in the absence of ingestions of mercury in the diet elsewhere, that this would not breach the recommended intake values for mercury.