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Technical Key to the Boletes of California

Key to the Genera of Boletes in California

1. Hymenophore (tubes) irregularly arranged, not vertically oriented; spore deposit not obtainable Gastroboletus
1. Hymenophore regular in arrangement, more or less vertically oriented; spore deposit typically readily obtained 2
2. Tubes and pores with clusters of cystidia in the hymenium that stain dark brown to blackish to occasionally vinaceous in a solution of potassium hydroxide Suillus
2. Darkly staining, clustered cystidia absent in hymenium 3
3. Basidiocarp with a dry, pulverulent bright yellow veil (be sure to check young specimens) Pulveroboletus
3. Basidiocarp without a veil 4
4. Pores white to pallid when young, becoming yellow at maturity; stipe hollow; spores ellipsoid, yellow in deposit Gyroporus
4. Basidiocarps without the above combination of characters 5
5. Surface of stipe with numerous relatively small squamules, which are usually pallid when young but become dark colored (dark brown to black) at maturity Leccinum
5. Surface of stipe not as above 6
6. Pores white, yellow, or red; spores brown, olive, olive brown, or yellow brown in deposit Boletus
6. Pores pink, vinaceous, gray brown to very dark brown (yellow in T. amylosporus); spores flesh color to vinaceous brown to reddish brown in deposit Tylopilus

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Key to the Sections of Boletus

1. Some spores in every mount truncate (flattened and/or slightly notched at the apex) Section Truncati
1. Spores not as above 2
2. Tubes and pores reddish to reddish brown; taste of context very acrid Section Piperati
2. Not as above 3
3. Pileus surface velutinous to subtomentose to tomentose or conspicuously fibrillose Section Subtomentosi
3. Pileus surface not as above 4
4. Surface of stipe reticulate, at least in the apical portion Section Boletus
4. Surface of stipe not reticulate 5
5. Pores pink to dark red Section Boletus
Subsection Luridi
5. Pores some shade of yellow, not pink or red Section Pseudoboleti

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Key to the Subsections of Section Boletus

1. Pores yellow when young Subsection Calopodes
1. Pores not yellow when young 2
2. Pores pink to deep red Subsection Luridi
2. Pores white when young Subsection Boleti

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Key to the Species of Subsection Boleti of Section Boletus

1. Pileus strongly reticulate or ridged, brown to dull yellow brown Boletus mottii
1. Pileus not as above 2
2. Pileus tan to light brown, surface viscid when wet Boletus edulis
2. Pileus dark brown to blackish brown, surface moist to dry Boletus aereus

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Key to the Species of Subsection Calopodes of Section Boletus

1. Taste of context bitter Boletus calopus var. frustosus
1. Taste of context mild 2
2. Pileus rose pink to red Boletus regius
2. Pileus not colored as above 3
3. Pileus dark brown; surface noticeably fibrillose; context unchanging when exposed Boletus fibrillosus
3. Basidiocarp not as above 4
4. Spores 12-14 µm long; hyphae of cuticle not incrusted; pileus glabrous; associated with oaks and other hardwoods Boletus appendiculatus
4. Spores 14-17 µm long; hyphae of cuticle with hyaline, spiral incrustations; pileus often with scattered fibrillose scales; associated with firs Boletus abieticola

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Key to the Species of Subsection Luridi of Section Boletus

1. Stipe reticulate 2
1. Stipe not reticulate 3
2. Pileus gray to pinkish gray; stipe conspicuously bulbous, pale pink to pallid Boletus satanas
2. Pileus brown to reddish brown; stipe clavate to subbulbous, brown Boletus eastwoodiae
3. Pileus yellow; spores 5-6 X 3-4 µm Boletus orovillus
3. Pileus not yellow; spores larger 4
4. Pileus pink to reddish vinaceous to vinaceous red; pores pink to reddish vinaceous Boletus amygdalinus
4. Pileus dark brown to reddish brown; pores red to deep red Boletus erythropus

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Key to the Species of Section Piperati

Only one species known from California Boletus piperatus

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Key to the Species of Section Pseudoboleti

1. Tubes changing to brick red when bruised or dried Boletus tomentipes
1. Tubes changing to blue when bruised 2
2. Pileus up to 10 cm broad, brown on the margin; hyphae of cuticle not incrusted; stipe cuticle differentiated as a cutis Boletus pulverulentus
2. Pileus up to 15 cm broad, tan to buff on the margin; hyphae of cuticle incrusted; stipe cuticle differentiated as a layer of basidia and caulocystidia Boletus fragrans

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Key to the Subsections of Section Subtomentosi

1. Spores up to 22 µm in length; pores yellow Subsection Mirabiles
1. Spores less than 20 µm in length, or if greater than that in length, the pores pink or reddish 2
2. Pileus red or reddish vinaceous Subsection Fraterni
2. Pileus not colored as above 3
3. Tubes and pores staining blue when bruised Subsection Subtomentosi
3. Tube and pores not changing to blue when bruised Subsection Versicolores

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Key to the Species of Subsection Fraterni of Section Subtomentosi

Only one species known from California Boletus coccyginus

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Key to the Species of Subsection Mirabiles of Section Subtomentosi

Only one species known from California Boletus mirabilis

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Key to the Species of Subsection Subtomentosi of Section Subtomentosi

1. Ammonium hydroxide giving a fleeting but distinct blue to blue-green reaction on the surface of the pileus 2
1. Ammonium hydroxide not giving a blue or blue-green reaction, but may give some other color when applied to the surface of the pileus 3
2. Pileus yellow brown to olive brown; trama not amyloid Boletus spadiceus var. spadiceus
2. Pileus reddish brown; trama amyloid Boletus spadiceus var. rufobrunneus
3. Spores large (15-22 µm in length), often highly irregular in outline; pores pink to red Boletus mendocinensis
3. Basidiocarp not with the above characters 4
4. Pileus dull olive brown to yellow brown; pores 1-3 mm broad Boletus subtomentosus
4. Basidiocarp not with the above characters 5
5. Pileus dark gray brown to almost black 6
5. Pileus differently colored 7
6. Pileus fuscous to almost black; surface pruinose; cuticular hyphae irregularly incrusted; stipe often dark red with age Boletus zelleri
6. Pileus gray brown; conspicuously tomentose to velutinous, not pruinose; cuticular hyphae spirally incrusted; stipe pallid or red or reddish at apex Boletus chrysenteron
7. Stipe red or red and yellow, abruptly pinched at the base; pileus dry, tomentose to velutinous, brown to red or a mixture of the two colors; found under coastal live oak (Q. agrifolia) Boletus dryophilus
7. Basidiocarp not as above; not found under coastal live oak 8
8. Pileus tan to buff, not red or reddish; tubes pale yellow; stipe yellow at the apex, red at the base, sometimes entirely red with age Boletus rubripes
8. Pileus red to reddish brown with olive or gray overtones; stipe red at the apex or with a red band in the apical region, often yellow or pallid at the base Boletus smithii

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Key to the Species of Subsection Versicolores of Section Subtomentosi

Only one species known from California Boletus flaviporus

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Key to the Species of Section Truncati

1. Most spores conspicuously truncate; pileus brown to olive brown, tomentose, dry; spores not amyloid Boletus truncatus
1. Only occasional spore with truncate apex; pileus red to reddish brown, glabrous, moist to subviscid (often viscid when wet); spores amyloid Boletus amyloideus

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Key to the Species Gastroboletus

1. Peridial membrane white, persistent, enclosing the gleba and well differentiated from the cuticle of the cap Gastroboletus subalpinus
1. Gastrocarp not with the above characters 2
2. At least 50 percent of the spores truncate and with a small germ pore Gastroboletus xerocomoides
2. Spores not as above 3
3. Hymenium with clustered, darkly staining cystidia when mounted in potassium hydroxide Gastroboletus suilloides
3. Hymenium without clustered cystidia 4
4. Context not turning blue when exposed; spores noticeably amyloid Gastroboletus amyloideus
4. Context bluing rapidly when exposed; spores not amyloid Gastroboletus turbinatus

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Key to the Species Gyroporus

Only one species known from California Gyroporus castaneus

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Key to the Sections Leccinum

1. Pileus margin with conspicuous segments or "flaps" of sterile tissue (check young basidiocarps) Section Leccinum
1. Pileus margin without sterile segments or "flaps" Section Scabra

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Key to the Species of Section Leccinum

1. Context of pileus and stipe unchanging or not becoming fuscous when exposed Leccinum constans
1. Context eventually changing to fuscous when exposed 2
2. Context becoming red to reddish brown before changing to fuscous 3
2. Context changing directly to fuscous 5
3. Cells of cuticular hyphae developing pigment globules when mounted in Melzer's reagent Leccinum aurantiacum
3. Pigment globules not developing in cells of cuticular hyphae when mounted in Melzer's reagent 4
4. Pileus pale brown to buff colored, viscid, changing to blue when bruised; context fading to white after darkening; found with madrone (Arbutus) Leccinum arbuticola
4. Pileus brown to reddish brown to rust brown, dry to subviscid, context not changing to blue, remaining dark colored after exposure; found with aspens (Populus) Leccinum discolor
5. Surface of pileus distinctly viscid 6
5. Surface of pileus moist to dry (sometimes subviscid when wet or old) 7
6. Pileus dark red; spores 4-5 µm broad Leccinum manzanitae var. manzanitae
6. Pileus colored as above; spores narrowly elongate, 3-4 µm broad Leccinum manzanitae var. angustisporum
7. Pileus dark dull brown to dark reddish brown; tubes and pores not becoming lavender when bruised Leccinum brunneum
7. Basidiocarp not as above 8
8. Pileus pale buff to pale pink; stipe white or whitish during all stages Leccinum armeniacum
8. Basidiocarp not as above 9
9. Pileus dark reddish brown; pores dark smoky olive; squamules on stipe small and densely crowded Leccinum largentii
9. Basidiocarp not as above 10
10. Pileus brick red to ferruginous; surface tomentose to fibrillose when young Leccinum insigne var. insigne
10. Pileus brown to reddish brown; surface glabrous when young Leccinum insigne var. brunneum

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Key to the Species of Section Scabra

1. Pileus gray to gray brown Leccinum montanum
1. Pileus whitish to pale tan or tan Leccinum californicum

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Key to the Species Pulveroboletus

Only one species known from California Pulveroboletus ravenelii

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Key to the Sections Suillus

1. Pileus dry to moist, fibrillose to fibrillose-scaly, or if viscid, then stipe annulate and without glandular dots on the surface, at least when young Section Boletinus
1. Pileus subviscid to viscid to glutinous; stipe without annulus or, if annulate, then surface with glandular dots Section Suillus

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Key to the Species of Section Boletinus

1. Surface of pileus dry to moist, fibrillose to fibrillose-scaly (check young basidiocarps) 2
1. Surface of pileus viscid to glutinous; glabrous to streaked or appressed fibrillose 3
2. Pileus dull red to reddish brown to orange buff; surface fibrillose-scaly; viscid layer below scales well developed Suillus lakei var. lakei
2. Pileus brick red to vinaceous tawny; scales prominent and more or less erect; viscid layer below scales poorly developed Suillus lakei var. pseudopictus
3. Context of pileus changing to blue then fuscous when exposed Suillus lithocarpi-sequoiae
3. Context of pileus not changing to blue, but may change to some other color and context of stipe may change to blue 4
4. Context of stipe, at least in the base, changing to blue when exposed 5
4. Context of stipe not changing to blue when exposed Suillus pseudobrvipes
5. Annulus viscid to glutinous, outer surface bright orange in young basidiocarps; pileus brown to reddish brown, often staining greenish with age Suillus ponderosus
5. Annulus moist to subviscid, pallid to white 6
6. Spores 7-9 µm long; pileus glabrous, cinnamon to orange cinnamon Suillus imitatus
6. Spores 8-11 µm long; pileus pallid, buff to pale vinaceous, streaked or with closely appressed fibrils Suillus caerulescens

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Key to the Species of Section Suillus

1. Context changing to blue when exposed 2
1. Context unchanging or not becoming blue when exposed 3
2. Surface of stipe distinctly reticulate Suillus reticulatus
2. Surface of stipe not reticulate Suillus tomentosus
3. Veil or false veil present, either forming an annulus or existing as a noticeable role of tissue on the pileus margin (check young basidiocarps) 4
3. Veil or false veil absent; margin glabrous or with scattered fibrils 18
4. Annulus typically present 5
4. Annulus typically absent 10
5. Pores very large, up to 5 mm broad; compound and often lamellate; annulus evanescent; pileus yellow to dark brown 6
5. Pores not more than 2 mm broad, usually smaller; annulus more or less persistent; pileus tan to pale brown to olive brown to dark brown 7
6. Pileus bright yellow; stipe short, often somewhat eccentric Suillus megaporinus
6. Pileus yellow brown; stipe well developed, not eccentric Suillus riparius
7. Stipe with noticeable glandular dots on the surface 8
7. Stipe without noticeable glandular dots Suillus pseudobrevipes
(see Boletinus Section)
8. Pores 1 mm or more broad; cap more or less umbonate; pileus pale brown to tan or pale olive brown Suillus umbonatus
8. Pores less than 1 mm broad; pileus usually some shade of brown 9
9. Annulus with a vinaceous gray to purplish layer or zone on the outer surface; spores 7-9 µm long Suillus luteus
9. Annulus lacking a vinaceous or purplish zone; spores 9-11 µm long Suillus subolivaceus
10. Pores large, up to 5 mm broad, often lamellate; annulus evanescent 11
10. Basidiocarp not with above characters 12
11. Pileus bright yellow; stipe short, often eccentric Suillus megaporinus
11. Pileus yellow brown; stipe well developed, not eccentric Suillus riparius
12. Pileus white then gray, becoming ochraceous brown when mature; associated with Monterey and knobcone pines Suillus pungens
12. Basidiocarps and/or mycorrhizal host not as above 13
13. Pileus white, soon becoming chocolate brown; associated with sugar pine Suillus brunnescens
13. Basidiocarps and/or mycorrhizal host not as above 14
14. Pileus dark cinnamon brown; stipe white when young, becoming ochraceous when mature Suillus borealis
14. Basidiocarp not as above 15
15. Pores 1-2mm broad; pileus dingy yellow; associated with white pine (Pinus monticola) Suillus sibiricus
15. Basidiocarps and/or mycorrhizal host not as above 16
16. Glands prominent on stipe during all stages; associated with Bishop pine Suillus glandulosipes
16. Basidiocarps and/or mycorrhizal host not as above 17
17. Pileus yellow to rust color when young, often spotted or mottled; spores 8-l0 X 3-4 µm Suillus volcanalis
17. Pileus white to pallid to pale vinaceous when young; spores 6-8 X 2.5-3 µm Suillus albidipes
18. Pileus surface conspicuously fibrillose-scaly 19
18. Pileus surface glabrous, may appear spotted or streaked from gluten with age 21
19. Pileus brown; pores large; associated with ponderosa pine Suillus californicus
19. Basidiocarps and/or mycorrhizal hosts not as above 20
20. Taste mild Suillus fuscotomentosus
20. Taste harsh, unpleasant Suillus acerbus
21. Stipe without conspicuous glandular dots 22
21. Stipe with noticeable glandular dots 23
22. Stipe clavate to ventricose; yellow to olive to olive buff to pale brown Suillus monticolus
22. Stipe more or less equal, often short, white to pallid Suillus brevipes
23. Context white, pores radiately arranged Suillus punctatipes
23. Context yellow, pores not radiately arranged Suillus granulatus

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Key to the Species Tylopilus

1. Tubes yellow; many spores truncate and amyloid Tylopilus amylosporus
1. Tubes differently colored; spores not as above 2
2. Pores very dark brown to dark reddish brown; cap black to dark smoky brown Tylopilus pseudoscaber
2. Basidiocarp not as above 3
3. Surface of stipe reticulate Tylopilus indecisus
3. Surface of stipe not reticulate or only at the apex 4
4. Stipe often short, eccentric, or poorly developed; basidiocarp rarely coming fully above the ground Tylopilus humilis
4. Basidiocarp not as above 5
5. Pileus very dark, dull brown Tylopilus ferrugineus
5. Pileus pale vinaceous to tan or drab Tylopilus ammiratii

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The Boletes of California
Copyright © 1975 by Dr. Harry D. Thiers
Additional content for the online edition © 1998 by Michael Wood, Fred Stevens, & Michael Boom
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