Boletus rubroflammeus is a species of bolete fungus in the family Boletaceae. First described from Michigan in 1971, it is found in the eastern United States and Mexico, where it grows in a mycorrhizal association with hardwood trees. The fruit bodies (mushrooms) of the fungus have caps that are deep red to purplish red, and dark red pores. The stem has coarse, dark red reticulations (raised, net-like ridges) and a narrow yellow area at the top. All parts of the mushroom quickly stain blue when injured or cut. Lookalikes include Boletus flammans, a lighter-colored species that grows with conifers. Other similar species can be distinguished by differences in distribution, morphology, staining reaction, and microscopic characteristics. Boletus rubroflammeus mushrooms are poisonous, and can cause gastrointestinal distress if consumed. Taxonomy The species was first described by American mycologists Alexander H. Smith and Harry D. Thiers in their 1978 monograph on the boletes of Michigan. The type collection was made by Smith near Ann Arbor, and is stored at the University of Michigan Herbarium. The specific epithet rubroflammeus derives from the Latin words ruber ("red") and flammeus ("flaming"). Description The shape of the cap of B. rubroflammeus is convex to broadly convex, and reaches a diameter of . The margin of the cap extends slightly beyond the tubes. The cap surface is dry and initially appears appressed-fibrillose (with fibrils pressed down flat against the surface) or has a matted grayish tomentum, but later the hairs slough off and the matted tomentum is present only along the cap margin. In maturity, the center of the caps develop slight cracks. The cap is a deep vinaceous-red color that remains constant throughout the life of the fruit bodies. The flesh is thick, soft, and yellow. Its taste is mild, and it has no distinct odor. On the underside of the cap, the spore-bearing surface comprises vertically arranged minute tubes with pore-like openings. The tubes are yellow, deep, initially adnate (fused) to the stem, but later becoming free from attachment (or nearly so). Individual pores are round and small (about 2 per mm), while the overall pore surface is uneven or pitted. Its color is initially deep red, but fades slightly in maturity; the pore surface quickly turns blue with injury. The stem is long, thick, solid (i.e., not hollow), and equal in width throughout to club-shaped. Inside, it is yellowish with reddish streaks. Most of the