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Summary: Features include 1) viscid or glutinous cap most often rich reddish brown with pale yellow margin but sometimes all yellow, 2) pale orange-yellow flesh that bruises pinkish brown, 3) pores that are creamy when young, then yellow, and then dingier, usually turning brownish or rusty where bruised, 4) stem that is yellow above annulus and streaked reddish brown to brown below it, 5) veil that may have a gelatinous outer layer and typically forms a gelatinous annulus, and 6) growth under larch. In western North America, the cap tends to be dark and cinnamon, but in Europe and eastern North America it is yellower, (Arora). Suillus proximus A. H. Smith & Thiers is considered by Bessette(3) to be a synonym. S. grevillei is found in northeastern North America, west to the Pacific Northwest and AK, (Bessette). It is very common in ID and MT where larch grows, (Arora), and is found in BC (Bandoni), WA (several observers) and OR (R. Bishop, pers. comm.; voucher at Oregon State University), as well as NS, NC, (Lincoff(2)), and also Europe and Asia (Breitenbach).
Cap: 3.5-14cm, convex, becoming broadly convex to nearly flat when old; "orange-yellow, dull red, red-brown, reddish brown, dark reddish brown or dark chestnut-brown"; bald, shiny, viscid to glutinous; margin with hanging veil remnants, (Bessette), 3-15cm, convex to nearly flat; deep red to reddish brown with a yellowish margin, varying to golden yellow throughout or yellow with a cinnamon-tinged to rusty-tinged center; smooth, viscid or slimy when moist, often shiny when dry, margin sometimes with veil remnants, (Arora), 5-15cm, hemispheric becoming broadly convex to nearly flat; "chestnut" on disc, "empire yellow" on margin, at times bright yellow over all (Ridgway colors in quotation marks); bald, glutinous, "pellicle separable, margin sterile", (Smith), sometimes umbonate (Lincoff(1)), typically deep reddish brown "with a distinct yellow margin, although forms with all-yellow caps occur", (Trudell)
Flesh: pale orange-yellow, bruising pinkish brown; in stem "yellowish, occasionally staining bright green, especially near the base when cut", (Bessette), thick; yellow but often aging or staining pinkish to reddish, not turning blue, (Arora), 1-1.5cm thick, "straw yellow" to "amber yellow", soon rubescent (becoming "salmon buff" or "flesh color"), in stem flavous to "primuline yellow" at first, sometimes slightly sulphur to greenish in base when cut, (Ridgway colors in quotation marks), (Smith), bright yellow, changing to pink or flesh color when exposed (Thiers)
Pores: 1-3 per mm, angular; yellow when young, darkening to olive-yellow or olive-brown when old, staining brownish where bruised; tube layer 0.4-1.2cm thick, adnate to depressed, (Bessette), often somewhat radially arranged; creamy when young becoming yellow and finally dingy ocher or olive-yellow, not turning blue but usually turning brownish or rusty where bruised; tubes adnate to decurrent, same color, (Arora), 1-2 per mm, angular, rather thick-walled; tube layer 1-1.5cm thick, adnate to depressed, becoming subdecurrent, "amber yellow" but finally "olive ochre", when bruised or cut becoming "testaceous" or "pecan brown", (Ridgway colors), (Smith)
Stem: 4-14cm x 1-3cm, nearly equal or widening slightly downward, solid; yellow and smooth above annulus, streaked reddish brown to brown in lower part and often whitish near base; glutinous to viscid; lacking glandular dots; "partial veil yellowish with reddish brown streaks, cottony with a gelatinous covering, forming a gelatinous superior annulus", (Bessette), 4-10cm x 1-3cm, equal or widening slightly in lower part, solid, firm; "pale yellow when young but soon mottled reddish to deep brown or cinnamon below the veil and often staining brown when handled"; glandular dots absent; veil "yellowish before breaking, the underside often viscid in wet weather", usually forming median to superior, cottony, whitish annulus, (Arora), 4-10cm x 1-3cm, equal to slightly clavate [club-shaped], solid; flavous to "primuline yellow" at first, soon with chestnut variegations, dingy when old, or after handling often with a vinaceous brown cast; distinctly reticulate above annulus from extensions of decurrent tubes; typically floccose annulus that may have a gelatinous outer layer, (Smith)
Chemical Reactions: cap surface greenish black with KOH; flesh displays a pink flash with KOH that immediately becomes blue to bluish black, flesh stains olive-brown to olive-black with application of FeSO4, (Bessette)
Odor: not distinctive or acid-metallic (Bessette), none to somewhat metallic (Smith)
Taste: not distinctive (Bessette), mild to slightly astringent to bitterish (Smith)
Microscopic: spores 8-10 x 2.5-4.5 microns, elliptic, smooth, pale straw to nearly colorless, (Bessette), spores 8-10 x 3-3.5 microns, elliptic to spindle-shaped, (Arora), spores 8-10 x 2.8-3.5 microns, more or less oblong, smooth, with a faint colorless outer sheath, pale olivaceous to ochraceous in Melzer's reagent and KOH; basidia not described; pleurocystidia numerous to scattered or rare, sometimes in fascicles [bundles], 40-60 x 6-8 microns individually, subcylindric to clavate, but some obscurely fasciculate, smooth, brownish to yellowish in KOH and Melzer's reagent, thin-walled, bister incrusting material at base only, cheilocystidia similar to pleurocystidia, "in fascicles, incrusted with bister pigment at level of hymenium, the bundles scattered to numerous"; cap cuticle a trichodermium of long gelatinous hyphae 3-6 microns wide, "the cells very long and narrow, end cells not differentiated"; caulocystidia single or in scattered small fascicles and with incrusting pigment as revived in KOH; clamp connections not seen, (Smith)
Spore Deposit: dull cinnamon-brown, (Bessette), olive-brown to dull cinnamon (Arora), olive brown when moist, dull cinnamon when dry, (Smith)
Habitat / Range
cespitose to gregarious, often in arcs and always associated with larch, (Smith), early summer to late fall (Miller)
Suillus luteus has a less brightly colored cap and a stem with glandular dots, and is not specific to larch, (Smith). Other boletes under larch include Suillus cavipes, S. ochraceoroseus, and S. viscidus.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2020. E-Flora BC:
Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for
Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2020-05-30 12:12:48 PM
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