Bitter bolete

Description

The bitter bolete is a bolete-type mushroom with a light brown or fleshy brown, suede-like cap up to 12–15 cm, with long tubes that are white when young and turn pink with age. The stem is paler than the cap and covered with a brown net with wide meshes. The flesh is white, does not change colour when cut and looks appetising, but is exceptionally bitter.

It grows from June to October, mainly in coniferous forests on acidic soils, in mycorrhiza with pine, but also under beeches and oaks. It is common in Poland.

Young fruiting bodies are often confused with the porcino and the brown birch bolete. The surest clues are the pores turning pink and the dark net on a paler stem. Do not rely on taste as a method of identification. One specimen can spoil a whole dish, because the bitterness intensifies during cooking.

Identification features

Cap

Diameter up to 12–15 cm (exceptionally up to 30 cm in North America). Hemispherical when young, then convex, finally flattened. Surface downy and suede-like at first, then smooth, matt. Colour light brown, fleshy brown, grey-yellow to nut-brown. The cuticle cannot be peeled off.

Hymenophore (underside of the cap)

Tubes long (2–3 cm), the pores project beyond the cap margin and are attached to the stem; they separate easily from the flesh. White when young, then pale pink; when damaged dirty wine-coloured, carmine or brownish, with rusty-brown spots with age. Pores small (1–2 per mm).

Stem

Height up to 14 cm (descriptions also give 7–10, rarely 20 cm), thickness 2–4 cm, up to 6 cm at the base; solid, barrel-shaped in young specimens, club-shaped in older ones, paler than the cap. Covered with a distinct brown net with wide meshes (dark on a pale background). No ring.

Flesh

White or cream, pinkish under the cap cuticle, may take on pinkish shades when cut; does not turn blue. Hard when young, soft and spongy in older specimens. Smell weak, pleasant or slightly unpleasant. Taste exceptionally bitter; it is not recommended to taste it, let alone eat it.

Spore print and spores

Spore print pink, brownish with a reddish or pink tint. Spores spindle-shaped to ellipsoid, smooth; size 10–17 × 3–6 µm (descriptions give different ranges).

Habitat and distribution

Ecology. A terrestrial mycorrhizal fungus, with pine and other coniferous and deciduous trees (often under beech and oak). Likes acidic, well-drained soils. Sometimes on trunks, stumps and rotting wood. Fruiting bodies are rarely attacked by insects; they may be parasitised by the mould Sepedonium ampullosporum. The fruiting bodies strongly accumulate radioactive caesium-137.

Distribution. North America (as far as Mexico and Central America), Europe, Asia (including Japan, Korea, China, Pakistan). Widespread in Europe; common in coniferous forests in Poland. Not legally protected in Poland.

Fruiting. From June to the end of October (in some regions until November).

What can it be confused with?

• Boletus edulis (porcino) — The pores of the bitter bolete turn pink with age (in the porcino white, then yellow-green); the net on the stem of the bitter bolete is dark on a pale background (in the porcino pale on a dark one); the flesh of the bitter bolete is very bitter.
• Boletus reticulatus (summer cep) — The flesh of the bolete is not bitter; pores yellowish with age, not pink.
• Leccinum scabrum (brown birch bolete) — Young specimens are sometimes confused; the bitter bolete has pink pores and a brown net instead of dark scales on the stem, and bitter flesh.
• Rubroboletus satanas (Satan's bolete) — Colloquially called "Satan", rare and poisonous; it has red pores.
• Boletus badius (bay bolete), Xerocomus subtomentosus (suede bolete) — Yellow tubes; the bay bolete has flesh that turns blue; the suede bolete has a slender stem and yellow pores.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• It is the only representative of the genus Tylopilus occurring in Europe and the type species of this genus.
• The bitterness does not affect people without a genetic sensitivity to bitter taste (the TAS2R38 gene); the compound responsible for the bitterness has not been identified.
• Despite its bitterness it is sometimes sold at markets in Mexico.
• The fruiting bodies strongly accumulate radioactive caesium-137 from the soil, which is attributed to the deep penetration of the soil by the mycelium.