Butyriboletus fuscoroseus
Butyriboletus fuscoroseus is a pored mushroom in the family Boletaceae. It was formerly considered a species of Boletus, but in 2014 was transferred to the newly created genus Butyriboletus. Boletus pseudoregius, a European taxon originally described as a subspecies of Boletus appendiculatus in 1927, is a synonym. B. fuscoroseus is considered critically endangered in the Czech Republic.
Description
Butyriboletus fuscoroseus produces a robust basidiocarp with a convex cap 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.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 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, each containing one to three large oil droplets. The basidia are club-shaped and four-spored, and the cystidia measure roughly 36–52 × 9–14.5 μm. The cap surface is a trichoderm of interwoven, slightly incrusted hyphae with rounded terminal cells. Chemical spot tests produce only slight reactions with ammonia and potassium hydroxide solution, and no change with iron(II) sulphate or Melzer's reagent.