| Tylopilus felleus|
(Bull.) P.Karst. (1881)
Tylopilus felleus, commonly known as the bitter bolete or the bitter tylopilus, is a fungus of the bolete family. Its distribution includes east Asia, northern Europe, and eastern North America, extending south into Mexico and Central America. A mycorrhizal species, it grows in deciduous and coniferous woodland, often fruiting under beech and oak. Its fruit bodies (mushrooms) have convex to flat caps that are some shade of brown, buff, or tan, and typically measure up to 15 cm (6 in) in diameter. The pore surface is initially white before turning pinkish with age. Like most boletes it lacks a ring, and it may be distinguished from Boletus edulis and other similar species by its unusual pink pores and the prominent dark brown netlike pattern on its stalk.
French mycologist Pierre Bulliard described this species as Boletus felleus in 1788 before it was transferred into the new genus Tylopilus. It is the type species of Tylopilus, and the only member of the genus found in Europe. Tylopilus felleus has been the subject of research into bioactive compounds that have been tested for antitumour and antibiotic properties. Although not poisonous, it is generally considered inedible, due to its overwhelming bitterness.