Bitter bolete has a wide distribution across east Asia, Europe, and North America. Recognized by its convex brown cap, white pores turning pinkish, and dark net-like stalk pattern, it forms mycorrhizal relationships with deciduous and coniferous trees. Despite its non-toxic nature, it is inedible due to its extreme bitterness. Some studies suggest potential bioactive compounds with antitumor and antibiotic properties.
The cap ranges from 4-16 cm (1.5-6.3 in) in diameter. Initially dome-shaped or hemispherical, it becomes flatter and sometimes even depressed with age, with edges often cracking and deforming. In young fruiting bodies, the margin is usually membranous and sterile (lacks tubes). Occasionally, this edge remains in that state, slightly overhanging the hymenophore. The surface is initially finely velvety, resembling suede, but later becomes dry, smooth or slightly rough, and slightly sticky in wet weather. The color varies from yellowish-brown to gray-pink, powdery, and light brown.
The tubes are sponge-like. Initially white or pale cream, they are adnate (broadly attached) or subcurrent (downward on the stem). With age, the color changes to pinkish, and the tubes become deeply indented around the upper part of the stem. When cut or bruised, the color intensifies to pink or reddish-brown.
The stem is 1-3 cm (0.4-1.2 in) in diameter and 4-10 cm (1.6-4 in) in length, sometimes cylindrical but more often thickening near the base. The surface is initially almost white, later turning yellowish or light brown, and is covered with a net-like pattern. This pattern initially does not differ much in color but usually becomes darker over time, turning brown or dark brown.
The flesh is white and dense. When bruised or cut, it does not change color sharply but may slowly turn to a flesh-toned or pinkish-brown. In areas of older damage, such as those caused by larvae, the color can also be altered.
Solitary or in small groups.
The spore print is clay-colored, brownish-pink, or wine-colored.
It grows in mixed forests, more often near broadleaf trees but sometimes with coniferous trees. It can be found on soil and decaying wood.
The taste is extremely bitter, sometimes with a burning aftertaste; odor not distinctive
The mushroom is inedible due to its intense bitterness, which only intensifies with cooking. There are people who, due to genetic factors, do not taste the bitterness. For them, consuming this mushroom wouldn't be as severe a mistake as for others, as it is not poisonous, just inedible.
Bitter bolete can be mistakenly confused with King bolete and other similar edible species of the Boletus genus.
The stem of the Bitter bolete is generally darker due to the fact that the reticulated pattern on its surface is darker than the rest of the stem, whereas in the King bolete, these lines are lighter.
The pores of the Bitter bolete are larger, and the tubes are looser. Most importantly, they have a pinkish hue, whereas the tubes and pores of the King bolete are white, yellowish, or olive, but never pink.
Boletus edulis does not have a pronounced taste, whereas all parts of Tylopilus felleus are extremely bitter.
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