Porcini or Scarletina bolete

Cap 7–30 cm across, spherical or hemispherical in young mushrooms, becoming cushion-shaped and spread out over time. The color varies from light brown to dark chestnut or reddish brown depending on light and forest type: caps are darker in spruce woods and lighter in pine forests.

The cap surface is dry, smooth or slightly wrinkled, and can be a little sticky in wet weather. The margin is even or slightly wavy, inrolled in young mushrooms. The skin doesn't peel.

The cap of the scarletina bolete is large and fleshy, reaching 5 to 20 centimeters across. When young it is neatly hemispherical, opening with maturity to convex and cushion-shaped. The cap surface is dry and velvety-felty to the touch, and may become slightly sticky in wet weather. The color ranges from warm chestnut and dark brown to yellowish brown, often with a faint reddish or olive tint. When pressed, the cap surface darkens, developing bluish spots.

The hymenophore is tubular and separates easily from the cap flesh. In young mushrooms the tubes are white, later turning yellow; in mature ones they're yellow-green or olive. The pores are small, round, uniform in color and don't change color when pressed.

Under the cap lies a tubular hymenophore with a very characteristic, warning feature — the pores here are a rich orange-red, sometimes even blood-red, while the tubes themselves stay yellow or olive-yellow. It's these red pores that make the mushroom look like poisonous species, so it calls for special care. The most important diagnostic trait is the instant, dramatic reaction to touch: just run a finger over the pores, and they immediately flood with a deep dark blue, almost inky color.

Stem massive, 5–20 cm tall and 3–10 cm thick, bulbous or club-shaped in young mushrooms, later cylindrical. Color from whitish to light brown. The surface is covered with a characteristic white or cream net pattern, most distinct in the upper part of the stem.

There's no ring and no volva. The base of the stem is often thickened.

The stem of the scarletina bolete is sturdy, dense and massive, 5 to 15 centimeters tall, often thickened toward the base. It's the stem that gave the mushroom its Ukrainian scientific and folk names: against a yellow-orange background, it is densely covered in tiny reddish and brown scale-like dots that feel like a grainy surface. Unlike its close relative the lurid bolete, the scarletina bolete has no net pattern — just this characteristic grainy "dusting". When touched, the stem turns blue just as quickly. There is no ring and no volva.

The flesh is dense, juicy and white, and doesn't change color when cut or damaged — this feature sets porcini apart from a number of poisonous lookalikes. In old fruiting bodies the flesh becomes spongy and yellowish.

The taste is mild, nutty and slightly sweet. The stem flesh is denser and more fibrous than the cap flesh.

The flesh of the scarletina bolete is thick, dense and springy, lemon yellow in a fresh cut. Its main feature is a lightning-fast reaction to air: as soon as you cut the mushroom, the flesh floods before your eyes with an intense dark blue, almost inky color, spreading from the edges to the center. This reaction is so fast and vivid that it's one of the most reliable features of the species. Near the base of the stem the flesh may have a reddish tint. Raw flesh tastes mild, with no bitterness, but you shouldn't taste it raw.

The smell is pleasant, unobtrusive, mushroomy with light nutty notes. With cooking and drying the aroma intensifies and takes on a deep, rich woody, foresty character. It's for dried porcini that the mushroom is so valued in cooking — no other dried mushroom gives such a pronounced taste and smell.

The smell of the scarletina bolete is faint, pleasant and typically mushroomy, with no sharp or unpleasant notes. It carries no warning at all and may well seem appealing, so when identifying this species, rely first and foremost on the pore color and the bluing reaction, not on the aroma.