stem surface is covered with coarse dark red reticulations, although near the top the color is yellow beneath the reticulations. All parts of the mushroom will quickly stain blue when cut, bruised, or otherwise injured. The mushroom is poisonous, and if consumed can cause gastrointestinal distress; typical symptoms include cramping, nausea, bloating, vomiting, and diarrhea. Boletus rubroflammeus produces an olive-brown spore print. The spores are smooth, roughly oblong to slightly ventricose (swollen) in face view, in profile view inequilateral, and have dimensions of 10–14 by 4–5 μm. Spores have a broad and shallow suprahilar depression (a depressed area on the dorsal side of the spore that was once attached to the sterigma). They are yellowish hyaline (translucent) in Melzer's reagent, and pale yellow-orange when mounted in a solution of potassium hydroxide (KOH). The basidia (spore-bearing cells) are club-shaped with a long pedicel (stalk), four-spored, and measure 30–40 by 8–9 μm. 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. Cheilocystidia (cystidia on gill edges) are abundant, 18–35 by 5–9 μm, and roughly similar in shape to the pleurocystidia. When mounted in KOH, the cheilocystidia have a dingy orange-yellow color, and walls that are smooth and thin. The tissue of the tubes is bilateral, meaning that they have a central strand of roughly parallel hyphae from which other hyphae diverge. The central strand comprises interwoven hyphae that are floccose and orange-yellow in KOH; the diverging hyphae continue into the hymenium to form a subhymenium that contain smooth hyphae measuring 4–6 μm wide. The cap has a cuticle consisting of tightly interwoven pressed-down hyphae that are usually 3–5 μm wide. 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. Clamp connections are absent from the hyphae of B. rubroflammeus. Similar species Distinctive field characteristics used to distinguish Boletus rubroflammeus from similar boletes include the deep purple-red cap and the reticulated stem. B. flammans is similar in appearance, but has a more variable cap color, ranging from dark red to brick-red or reddish-brown, a yellow stem base and less prominently reticulate stem, and it grows under conifers. Rubroboletus rhodosanguineus is also very similar but has more variable cap color with brown to olive tones and its