Chalciporus piperatus, commonly known as the peppery bolete, is a small pored mushroom of the family Boletaceae found in mixed woodland in Europe and North America. It has been recorded under introduced trees in Brazil, and has become naturalised in Tasmania and spread under native Nothofagus cunninghamii trees. A small bolete, the fruit body has a 1.6–9 cm (0.6–3.5 in) orange-fawn cap with cinnamon to brown pores underneath, and a 4–9.5 cm (1.6–3.7 in) high by 0.6–1.2 cm (0.2–0.5 in) thick stipe. The rare variety hypochryseus, found only in Europe, has yellow pores and tubes.
Described by Pierre Bulliard in 1790 as Boletus piperatus, it is only distantly related to other members of the genus Boletus and was reclassified as Chalciporus piperatus by Frédéric Bataille in 1908. The genus Chalciporus was an early branching lineage in the Boletaceae and appears to be related to boletes with parasitic properties. Previously thought to be ectomycorrhizal (a symbiotic relationship that occurs between a fungus and the roots of various plant species), C. piperatus is now suspected of being parasitic on Amanita muscaria. The flesh of C. piperatus has a very peppery taste, and can be used as a condiment or flavoring.
One of the smaller boletes, Chalciporus piperatus has an orange-fawn 1.6–9 cm (0.6–3.5 in) cap that is initially convex before flattening out in age. The cap surface can be furrowed; shiny when dry, it can be a little sticky when wet. The colour of the pore surface ranges from cinnamon to dark reddish brown in maturity. When bruised, the pore surface stains brown. Individual pores are angular, measuring about 0.5–2 mm wide, while the tubes are 3–10 mm deep. Slender for a bolete, the stipe measures 4–9.5 cm (1.6–3.7 in) long by 0.6–1.2 cm (0.2–0.5 in) thick, and is either roughly the same width throughout its length, or slightly thicker near the base. The colour of the stem is similar to the cap, or lighter, and there is yellow mycelium at the base. The flesh is yellow, sometimes with reddish tones, maturing to purplish brown. It has no odour. The spore print is brown to cinnamon. Variety hypochryseus is essentially identical to the main form except for its bright yellow tubes and pores. Variety amarellus has pinker pores and a taste that is bitter rather than peppery.
The spores are smooth, narrowly fusiform (fuse-shaped), and measure 7–12 by 3–5 µm. The basidia (spore-bearing cells) measure 20–28 by 6–8 µm and are hyaline (translucent), four-spored, and narrowly club-shaped, with many internal oil droplets. Cystidia are fusiform, sometimes with a rounded tip, and have dimensions of 30–50 by 9–12 µm. Some are more or less hyaline, while others are encrusted with a golden pigment. The cap cuticle is a trichodermium, an arrangement in which the outermost hyphae emerge roughly parallel, like hairs, perpendicular to the cap surface. These hyphae are 10–17 µm wide and have elliptical to cylindrical cells at their ends that are not gelatinous. Clamp connections are absent from the hyphae.