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Description

The cap is chestnut, rusty, olive brown, or dark brown in color and generally 4–10 cm (rarely to 13 cm) in diameter at maturity The cap has a distinctive conical shape, later flattening out. It is slimy to the touch, bare, smooth, and glossy even when dry, and the cuticle is easily peeled off. The tiny, circular pores of the tubes are initially yellow but turn olive to dark yellow with maturity. Like the skin of the cap, they can be readily peeled away from the flesh.

Tubes comprising the hymenophore on the underside of the cap are 3–7 mm (0.1–0.3 in) deep, with an attachment to the stipe ranging from adnate to somewhat decurrent. The pores are tiny, numbering 3 per mm in young specimens and 1–2 per mm in maturity. The stipe is 5–10 cm (2.0–3.9 in) tall and 2–3 cm (0.8–1.2 in) wide. It is pale yellow and more or less cylindrical but may bear a swollen base. A membranous partial veil initially links the stipe with the edge of the cap. When it ruptures, it forms a membranous, hanging ring. The top side of the ring is whitish, while the underside is characteristically dark brown to violet. This species is one of the few members of the genus Suillus that have such a ring. Above the ring, the stipe features glandular dots—minute clumps of pigmented cells. Below the ring, the stipe is dingy white, sometimes streaked with brownish slime. In humid conditions, the ring has a gelatinous texture. The white flesh of the entire fungus does not discolour when damaged, and is soft—particularly in mature specimens. It has a "pleasant" taste and lacks any distinctive odour. The spore print is ochre or clay coloured, the elongated elliptical spores measuring 7–10 by 3–3.5 µm. Basidia (spore-producing cells) are four spored, with dimensions of 14–18 by 4–5 µm. Cystidia are present on both the tube faces (pleurocystidia) and edges (cheilocystidia), either scattered or, more rarely, as bundles. They measure 20–35 by 5–7 µm and have a narrow club shape. Clamp connections are not present in the hyphae of S. luteus.

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