Tylopilus felleus is very bitter and unpalatable.

Tylopilus felleus and Boletus edulis (porcini) look similar and are often confused.

However, they can be distinguished by the reticulation on the stalk; in porcini, it is a whitish, net-like pattern on a brownish stalk, whereas in Tylopilus felleus it is a dark pattern on white. Porcini have whitish pores while the other has pink.

If in doubt, as to the species taste a tiny bit of flesh. Tylopilus felleus is strongly bitter while Porcini has a mild, more pleasant taste.

In light of evidence suggesting that up to 25% of people cannot taste some bitter compounds, recommending a taste test to confirm the identification of some mushroom is potentially dangerous. Although there have been no reports of illness or death from T. felleus, I doubt anyone would recommend eating the same quantity of it as many people eat Boletus edulis. (from Mushroom Expert.com)