The stem has coarse, dark red reticulations (raised, net-like ridges) and a narrow yellow area at the top.

Its color is initially deep red, but fades slightly in maturity; the pore surface quickly turns blue with injury.

[1] The mushroom is poisonous, and if consumed can cause gastrointestinal distress; typical symptoms include cramping, nausea, bloating, vomiting, and diarrhea.

Pleurocystidia (cystidia on the tube faces) are rare to scattered, 28–37 by 9–15 μm, fusoid (somewhat spindle-shaped) to ventricose, and have a somewhat sharp tip.

The hyphae in the epicuticular zone (a waxy layer on the surface of the cuticle) often have fine granular incrustations that can be seen in both KOH and Melzer's reagent.

[1] Distinctive field characteristics used to distinguish Boletus rubroflammeus from similar boletes include the deep purple-red cap and the reticulated stem.

Rubroboletus rhodosanguineus is also very similar but has more variable cap color with brown to olive tones and its cut flesh has an odor of overripe fruit that intensifies when dry.

[1] Another European species, B. permagnificus, has larger spores (13–16 by 5–6.5 μm), weakly decurrent pores, and only associates with oak trees.

[5] In addition to its geographic location, the Colombian species B. pyrrhosceles can be distinguished from B. rubroflammeus by its reddish-brown cap (fading to brownish orange in maturity), a brownish-red to deep red stem that is reticulated only at the top, and shallower tubes—up to 5 mm (0.2 in).

[7] Boletus rubroflammeus is a mycorrhizal species, and its fruit bodies grow scattered or in groups on the ground under hardwood trees.