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Key to Boletus in North America (Page Six)

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[Pore surface not red or orange; pore surface bruising blue to greenish blue (quickly or slowly), or cut flesh staining blue to bluish on exposure (quickly or slowly); stem not reticulate, or merely faintly so at apex; mature cap typically greater than 4-5 cm across; found east of the Rocky Mountains; pore surface yellow.]


Note: This key is in bad need of revision. The non-dichotomous format is annoying and, with the hindsight of a few years, I see many areas that require different emphasis, fleshing out, paring down, and so on. Don't hold your breath waiting, but I will eventually revise the key completely.


  • Cap yellow. (1/3)

      Flesh bluing quickly; stem red below, yellow above; under hardwoods; cap yellow-brown with KOH; spores 9-12 x 3-3.5 µ. (1/7)

      Boletus carminipes

      Cap usually with yellow powder; flesh sometimes bluing slowly or not bluing; stem reddish over yellow base color, sometimes with yellow powder; under pine; chemical reactions not recorded; spores 6-9 x 2.5-4 µ. (2/7)

      Boletus hemichrysus

      Flesh bluing quickly; stem yellow above, dark red to brownish red below; under hardwoods or conifers; chemical reactions not recorded; spores 12-17 x 4-6 µ. (3/7)

      Boletus luridellus

      Flesh bluing slowly and weakly; stem yellowish to brownish yellow, often white at apex; under hardwoods; cap margin pale blue-green, center dark brown with ammonia; spores 8.5-11.5 x 3.5-5 µ. (4/7)

      Boletus melleoluteus

      Flesh staining reddish, then bluish "within five minutes"; stem yellow, staining reddish in age; under hardwoods or conifers; cap reddish brown with ammonia; spores 10-14 x 4.5-6 µ. (5/7)

      Boletus ochraceoluteus

      Flesh bluing quickly; stem yellow, sometimes with reddish tints near base; under hardwoods or conifers; blued flesh orange with KOH; spores 10-16 x 4-6 µ. (6/7)

      Boletus pseudosulphureus

      Flesh bluing, but sometimes slowly or weakly; stem yellow, without red shades; "on sawdust, or on stumps or the surrounding soil"; chemical reactions not recorded; spores 7-9 x 3-4 µ. (7/7)

      Boletus sphaerocephalus

  • Cap olive, tan, brown, dark brown, or reddish brown--but not pink, red, or brick red. (2/3)

      > Cap pale (whitish, light tan, buff, etc.) in all stages of development. (1/2)

        ° Blue staining typically weak and erratic (or absent); cap 4.5-15 cm; stem whitish, developing brownish streaks (rarely developing reddish tones near base); cap rusty orange with ammonia; found under hardwoods. (1/4)

        Boletus pallidus

        ° Blue staining typically pronounced, though not strong; cap 4-12 cm; stem pale to yellowish, becoming reddish; cap negative with ammonia; found under oak and hemlock. (2/4)

        Boletus inedulis

        ° Blue staining typically weak and erratic (or absent); cap 5-25 cm; stem yellowish to whitish (rarely developing dull reddish tones); cap orange with ammonia; found under hemlock. (3/4)

        Boletus huronensis

        ° Blue staining typically pronounced, though not strong; cap 6-13 cm; stem yellowish to whitish, with red areas, and with a narrow red zone at the apex; cap reaction to ammonia not recorded; found under oak. (4/4)

        Boletus glabellus

      > Cap more highly colored. (2/2)

        ° Easily recognized species: (1/2)

          ~ Growing on or near conifer stumps; blue staining typically weak and erratic or absent; stem with yellow basal mycelium; spores 6-10 x 3-4 µ. (1/5)

          Boletus lignicola

          ~ Cap dark brown to olive brown, becoming cracked in age and revealing reddish flesh in the cracks; spores 9-13 x 3.5-4.5 µ . (2/5)

          Boletus chrysenteron

          ~ Cap chestnut brown to cinnamon brown, smooth; stem yellowish, adorned with tiny red fibers, dots, or spots; blue staining weak and erratic or absent. (3/5)

          Boletus subglabripes

          ~ Cap chestnut brown to cinnamon brown, conspicuously corrugated and rugged. (4/5)

          Boletus hortonii

          ~ Cap smoky buff to yellowish brown; stem whitish to yellowish or reddish, with a red zone near the apex; pore surface bruising blue, but then brown; flesh blue on exposure but soon fading to white. (5/5)

          Boletus glabellus

        ° Not as any of the above species: (2/2)

          ~ Blue staining or bruising faint and/or erratic. (1/2)

            * Cap surface turning green, blue or olive with a drop of ammonia--or with a flash of green before turning some other color. (1/2)

              -- Flashing green with ammonia and then resolving to another color. (1/2)

                Cap color dull brownish; cap surface orange with ammonia (after the green flash); stem yellow above, whitish below, occasionally with reddish tints. (1/2)

                Boletus huronensis

                Cap color dark olive to yellowish brown or brown, sometimes with reddish tints; cap surface reddish brown with ammonia (after the green flash); stem yellowish and whitish, sometimes staining brownish but never with reddish colorations. (2/2)

                Xerocomus ferrugineus

              -- Remaining greenish, bluish, or olive with ammonia; not merely flashing. (2/2)

                Cap color reddish to yellowish brown, sometimes with olive shades; cap surface green to blue with ammonia; flesh white when fresh; stem brownish or reddish brown; under hardwoods or conifers; northern in distribution. (1/2)

                Boletus badius

                Cap color tawny brown to yellowish brown; cap surface blue to greenish blue with ammonia; flesh yellowish; stem yellow to tawny or brownish; under hardwoods; southern in distribution. (2/2)

                Boletus hypoxanthus

            * Cap surface turning some other color with a drop of ammonia, and not flashing green at first. (2/2)

              Cap surface reddish brown with ammonia; cap color reddish to purplish brown; spores 7-10 µ long; under hardwoods or conifers; Texas. (1/3)

              Boletus lewisii

              Cap surface yellowish with ammonia; cap color variable--from yellowish brown to reddish brown or brownish; spores 10-13 µ long; under hardwoods; probably widely distributed east of the Rocky Mountains. (2/3)

              Boletus rufomaculatus

              Cap surface reddish brown with ammonia; cap color olive-brown to yellow-brown; spores 10-15 µ long; under hardwoods or conifers; widely distributed. (3/3)

              Xerocomus subtomentosus

          ~ Blue staining or bruising consistent and fairly strong. (2/2)

            * Cap surface bruising bluish or brownish. (1/2)

              -- Pore surface intially yellowish, but soon yellow-brown. (1/2)

              Boletus subgraveolens

              -- Not as above. (2/2)

                Cap surface yellowish with ammonia; flesh bluing when sliced, then slowly changing to to reddish brown; smell not distinctive; known only from Mississippi. (1/3)

                Boletus mahoganicolor

                Cap surface flashing green with ammonia; flesh bluing when sliced, but not changing to reddish brown; smell not distinctive; widely distributed east of the Rocky Mountains. (2/3)

                Boletus pulverulentus

                Cap surface yellow with ammonia; flesh bluing when sliced, but not changing to reddish brown; smell distinctively fragrant/spicy; widely distributed east of the Rocky Mountains. (2/3)

                Boletus sensibilis

            * Cap surface not bruising. (2/2)

              -- Spores reaching lengths of 16-19 µ or more. (1/2)

                Cap yellowish to brownish yellow, or streaked brownish over a yellow base color; stem not bruising when handled; spores 12-17 x 4-6 µ. (1/2)

                Boletus luridellus

                Cap reddish brown to tawny, fading to dull brown; stem bruising blue when handled; spores 13-19 x 5-8 µ. (2/2)

                Boletus rubricitrinus

              -- Not as above; spores typically shorter than 16 µ. (2/2)

                Flesh whitish, turning yellow then bluish near the tubes on exposure; cap reddish brown to yellow brown; stem brown to reddish brown, without yellow shades; cap surface green to blue with ammonia; widely distributed ERM (east of the Rocky Mountains). (1/8)

                Boletus badius

                Flesh pale yellow, bluing on exposure; cap reddish brown becoming yellow brown; stem yellow above, carmine red below; cap surface ammonia reaction not recorded; northeastern in distribution. (2/8)

                Boletus carminipes

                Flesh pale yellow, bluing on exposure but sometimes slowly; cap brownish to pale brownish; stem yellow at apex, yellowish or whitish overall; cap surface flashing green, then resolving to orange with ammonia; northeastern in distribution. (3/8)

                Boletus huronensis

                Flesh yellow, bluing quickly on exposure but slowly resolving to reddish brown; cap mahogany brown; stem yellow above, orange-red to brownish red below; cap surface yellowish with ammonia; recorded from Mississippi. (4/8)

                Boletus mahoganicolor

                Flesh pale yellow to whitish, red under the cap skin, bluing on exposure (the species name refers to the red, white and blue flesh); cap olive becoming reddish or brownish red; stem with red and olive shades over a yellow base color; cap surface olive amber with ammonia; widely distributed ERM. (5/8)

                Boletus patrioticus

                Flesh bright yellow, bluing quickly on exposure; cap reddish brown fading to cinnamon or yellow-brown; stem yellow, with reddish tinges; cap surface flashing blue, then dull purple with ammonia; probably widely distributed ERM. (6/8)

                Boletus pseudosensibilis

                Flesh whitish to pale yellow, bluing on exposure; cap olive brown to grayish brown, fading in age; stem yellow at apex, red or yellow with red areas below; cap surface dark olive green with ammonia; northeastern in distribution. (7/8)

                Boletus roseipes

                Flesh pale yellow, slowly bluing on exposure (at least above the tubes) but sometimes weakly; cap color variable--typically rusty brown to brownish, with paler areas that predominate in age; stem yellow at apex, yellowish or reddish below; cap surface yellowish with ammonia; probably widely distributed ERM. (8/8)

                Boletus rufomaculatus

  • Cap pink, red, or brick red. (3/3)

    The species below are notoriously difficult to separate. See also the small, red-capped bruisers with smooth stems, yellow pore surfaces, and eastern distribution.

      > Spores reaching lengths of 15 µ or more. (1/2)

        Flesh bluing slowly on exposure; cap surface reaction with ammonia not recorded; stem completely red; spores strongly amyloid, 14-17 x 4-5.5 µ; recorded from Michigan. (1/5)

        Boletus bicoloroides

        Flesh bluing promptly or slowly on exposure; cap surface orange-yellow to amber brown (often with a bluish ring) with ammonia; stem yellow, with reddish or brownish shades near the base; spores 10-15 x 4-6 µ; widely distributed east of the Rocky Mountains (ERM). (2/5)

        Boletus miniato-olivaceus

        Flesh bluing promptly or slowly on exposure; cap surface negative with ammonia; stem yellow, developing reddish shades; spores 11-17 x 3-5 µ; probably widely distributed ERM. (3/5)

        Boletus miniato-pallescens

        Flesh bluing promptly or slowly on exposure; cap surface negative with ammonia; stem yellow with reddish shades, becoming olive brown, bruising instantly; spores 11-17 x 4-6 µ; New Jersey to Florida to Texas. (4/5)

        Boletus oliveisporus

        Flesh bluing promptly on exposure; cap surface olive with ammonia; stem yellow above, red to purplish red below, slowly bruising olive; spores 13-19 x 5-8 µ; New Jersey to Florida to Texas. (5/5)

        Boletus rubricitrinus

      > Spores not reaching 15 µ. (2/2)

        ° Spores 5-7 µ long; cap slimy when wet and fresh; flesh in cap yellow with a reddish line under the cap skin, bluing and then turning slowly whitish when exposed; stem flesh yellow above, yellow and reddish below, yellow areas bluing when exposed. (1/2)

        Boletus purpureorubellus

        ° Not as above. (2/2)

          ~ Flesh bluing quickly on exposure. (1/2)

            Cap dull cinnamon to red, fading to yellowish brown; cap surface reaction to ammonia not recorded; stem yellow above, carmine red below; spores 9-12 x 3-3.5 µ; northeastern in distribution. (1/4)

            Boletus carminipes

            Cap mahogany to reddish brown; cap surface yellowish with ammonia; stem yellow above, reddish below, bruising blue; spores 10-13 x 3.5-4 µ; known from Mississippi. (2/4)

            Boletus mahoganicolor

            Cap rosy red to pinkish, becoming rosy tan; cap surface orange-yellow to amber brown (with a bluish ring) with ammonia; stem yellow, sometimes with reddish to brownish tinges; spores 10-15 x 4-6 µ; probably widely distributed east of the Rocky Mountains. (3/4)

            Boletus miniato-olivaceus

            Cap dark brick red, fading to sull rose or cinnamon; cap surface yellow with ammonia; stem yellow, sometimes with reddish to pinkish tinges at base, bruising quickly blue; spores 10-14 x 3.5-4.5 µ; probably widely distributed east of the Rocky Mountains. (4/4)

            Boletus sensibilis

          ~ Flesh bluing slowly and/or erratically on exposure. (2/2)

            Cap surface negative with ammonia; stem yellow above, red below; spores 8-12 x 3.5-5 µ; widely distributed east of the Rocky Mountains (ERM). (1/6)

            Boletus bicolor

            Cap surface bright reddish brown with ammonia; stem yellow above, reddish brown below, with brownish dots; spores 7-10 x 3.5-4.5 µ; Texas. (2/6)

            Boletus lewisii

            Cap surface orangish to amber brown, often with a bluish ring, with ammonia; stem yellow, sometimes with reddish or brownish tones near the base; spores 10-15 x 4-6 µ; widely distributed ERM. (3/6)

            Boletus miniato-olivaceus

            Cap surface olive with ammonia; stem yellow above, pinkish to reddish downward, bruising blue; spores 9-12 x 3.5-5.5 µ; known from NY, WV and NC; probably widely distributed in northern states ERM. (4/6)

            Boletus pallidoroseus

            Cap surface olive amber with ammonia; stem red and yellow, sometimes with olive shades; spores 10-13 x 4-5.5 µ; NC to FL, west to OH and TX. Exposed flesh red, white, and blue. (5/6)

            Boletus patrioticus

            Cap surface reaction to ammonia not recorded; stem yellow above, reddish below; spores 10-13 x 4-5 µ widely distributed ERM. Cap typically small, 2-8 cm across. (6/6)

            Boletus rubellus



    Cite this page as:

    Kuo, M. (2003, June). Key to Boletus in North America (page six). Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/boletus_06.html


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