Bondarzewia mesenterica (synonym: Bondarzewia montana) is a species of polypore fungus in the family Bondarzewiaceae.
The species was first described as Boletus mesentericus by Jacob Christian Schäffer in 1774. Hanns Kreisel transferred it to the genus Bondarzewia in 1984.
In maturity, a contiguous fruit body mass may be up to across. The caps are up to wide and tomentose with brownish zones, fan-shaped, often overlapping and growing from a shared base. The buff pores are up to wide. The flesh is whitish with a pleasant odour when fresh. The stalks are continuous with the caps and grow from an underground base, the sclerotium, which is up to 12 cm long and 5 cm thick.
Outside of its genus, it resembles Meripilus giganteus.
The species grows at the base of conifers. It affects tree bases and roots with a white rot.
The mushroom is considered edible, but is tough and often bitter.