Rheubarbariboletus armeniacus

Description
Mushroom Identification
Synonyms

Description

Rheubarbariboletus armeniacus is a small edible mushroom in the family Boletaceae native to Europe. It was formerly placed in the genera Boletus, Xerocomus, and Xerocomellus. It acquired its current name when it was transferred to genus Rheubarbariboletus in 2015. Fruitbody medium to small-sized, boletoid, without veil and ring. Stipe solid, often tapering towards the base. Flesh variously colored, changing or not when exposed to air. Tubes are not separable from each other, instead of tearing apart. Pores are usually angular.

It has been recorded to form an ectomycorrhizal association with white poplar (Populus alba) in Hungary. Its ectomycorrhizae contain bright yellow pigments, especially the rhizomorphs, and have warts on the outer surfaces of both the rhizomorphs and the mantle. The ectomycorrhizae of R. armeniacus cannot be reliably distinguished from those of Xerocomus subtomentosus.

Mushroom Identification

Cap

The cap is initially globular before expanding to become convex and flattening somewhat; it grows to a diameter of 2–6 cm (3⁄4–2+3⁄8 in). The cap margin initially adheres to the stipe and tends to become lobed or undulated in age. The cap surface is first somewhat pubescent but later becomes smooth and hairless, and may develop cracks in age. Its color is orangish-apricot, aging to ochre.
Tubes Initially pale yellow, but become more vivid in age, and eventually develop greenish-yellow to greenish-olive tones. They will become pale blue upon with bruising.
Pores

The pores are circular or a bit angular, with the same coloring and bruising reaction as the tubes.
Stem

The robust stem measures 3–8 cm (1+1⁄8–3+1⁄8 in) long by 0.5–1.5 cm (1⁄4–5⁄8 in) thick. It is usually thicker in the middle or lower region and its base roots into the substrate. The top part of the stem is yellow; under this, the coloration tends to be masked by a dense and fine reticulation that becomes brown to brownish-crimson in age. In some specimens, the stem cuticle cracks and pointed patches lift from the surface.
Flesh

The flesh is pale yellow in the cap, with a narrow strip of pinkish-yellow under the cuticle; in the stem, the flesh is orange-ochre, with a reddish tint. The flesh sometimes shows a slight and temporary color change to blue when cut or otherwise injured, but this feature is not consistent.
Odor and Taste

It has a pleasant odor and a fruity-acid taste.
Spores

Fusiform (spindle-shaped), measuring 10–15 by 4.5–6 µm. The basidia (spore-bearing cells) are club-shaped, four-spored, and contain internal oil droplets; they measure 28–35 by 9–12 µm. The cystidia are fusiform, hyaline (translucent), and 40–55 by 9–12 µm.
Spore Print

Olive brown.