Butyriboletus fuscoroseus produces a robust
basidiocarp with a convex cap (
pileus) up to 20 cm across. Young caps are hemispherical before flattening, and display colours ranging from violet-brown to reddish-brown, occasionally dull red; older specimens often fade to beige with a faint pink tint. The margin typically retains remnants of the
partial veil (appendiculate). Beneath the cap, the
tubes measure up to 1.5 cm long and are bright yellow, developing an olive tinge with age; both tubes and pores bruise blue when handled. The
stipe is stout, up to 10 cm long and 3 cm thick, cylindrical to club-shaped, yellow near the apex and tinged pink to red towards the base, usually with a well-developed reticulation of the same colour; it too bruises blue on handling. The context (
flesh) is whitish in the cap and lemon yellow in the stipe, shading to clay pink at the stipe base and turning blue on exposure. The odour is indistinct in young fruit bodies but in maturity may become medicinal or paint-like, and when dried can resemble smoked meat or chicory; taste is mild to slightly acidic. Microscopically, the
spores are
ellipsoid, measuring about 10–14.5 × 4–5.5
micrometres (μm), each containing one to three large oil droplets. The
basidia (spore-bearing cells) are club-shaped and four-spored, and the
cystidia measure roughly 36–52 × 9–14.5 μm. The cap surface (
pileipellis) is a trichoderm of interwoven, slightly incrusted
hyphae with rounded terminal cells. Chemical spot tests produce only slight reactions with
ammonia (NH4OH) and
potassium hydroxide (KOH) solution, and no change with
iron(II) sulphate (FeSO4) or
Melzer's reagent. ==Habitat and distribution==