E-Flora BC: Electronic Atlas of the Flora of British Columbia

Summary:
Features include 1) a dry, velvety cap that is dark olive-brown to grayish brown or vinaceous brown with whitish to yellow or pinkish flesh showing in the cracks, 2) flesh that may turn blue erratically and shows red in stem and around larval tunnels, 3) yellow pores that sometimes have reddish tints and that turn blue when bruised, 4) stem that is reddish or with red striations over a yellow base, some becoming brownish, olive-gray, reddish, or reddish brown, often with a red band at the top, 5) growth under conifers, alder or oak, and 6) microscopic characters that include weakly to distinctly amyloid spores, most with a truncate apex. |Siegel(2) say (in the California context), "There are three species that have been lumped under the incorrectly applied name X. chrysenteron, with X. diffractus being the most common and widespread of the bunch. X. amylosporus typically has a darker cap with more scattered and irregular cracks, the pores bruise dark inky blue, the stipe develops dingy brownish tones, and the spores are more reddish brown in color." X. salicicola is similar but much rarer, and "can be told apart by its more-often cracked cap and growth with willow", (Siegel(2) with Latin names italicized). |X. amylosporus is uncommon, but rather widespread, (Frank(9)). |Collections in dry habitats tend to form gastroid fruiting bodies, "and many Sierra Nevada collections are deformed", (Frank(9)). |The ITS sequence of the type of Gastroboletus xerocomoides is identical to that of the type of Xerocomellus amylosporus. Note that while about half of the spores of Gastroboletus xerocomoides were truncate as in X. amylosporus, the spores were described as inamyloid and wider, measuring 12.8-18(21) x 6.4-8 microns.

The known distribution is Pacific Northwest, north to at least Vancouver Island BC, south into CA, east to the Northern Rocky Mountains; collections were examined from WA, OR, ID (including holotype), and CA (including type of Gastroboletus xerocomoides), (Frank(9)). Xerocomellus amylosporus is found in ID (Smith), the northern Rocky Mountains and CA (Bessette).

Cap:
4-10cm across, bun-shaped becoming convex to flat; "dark olive brown to grayish brown, to vinaceous brown", "in cracks dull whitish to yellow, becoming pinkish in age"; "dry, finely velvety to matted-tomentose, lacking cracks when young, becoming areolate around the margin, to extensively areolate in age", (Frank(9)), 4-12cm, convex becoming broadly convex to nearly flat when old; dark olive-brown to grayish brown, yellow to dull whitish flesh showing in cracks; dry, velvety-subtomentose, become cracked and scurfy when old, (Bessette), 4-12cm, convex becoming broadly convex; dark olive-fuscous becoming olive-brown to olive-buff; dry, velvety, when old areolate [cracked like dried mud] or merely cracked, (Smith)

Flesh:
in cap "firm to soft, light yellow, erratically bruising blue", (Frank(9)), yellow to dull whitish, turning blue erratically or sometimes not changing when exposed, (Bessette), pale yellow except red just under cap surface, staining blue when cut and slowly becoming red around larval tunnels; in stem red, (Smith)

Pores:
1-2 per mm, "slightly angular or irregular", "yellow to golden yellow at first, becoming olive yellow, bruising inky blue to dark blue somewhat quickly"; tube layer slightly sunken around stem, (Frank(9)), 1-2 per mm, angular; "yellow, becoming golden yellow to dull yellow or olive-yellow", sometimes with reddish tints, turning blue when bruised; tube layer 0.8-2cm thick, depressed near stem when old, (Bessette), large and irregular in outline when mature, greenish yellow, readily staining blue; tube layer 1-1.5cm thick, ventricose, dull yellow to greenish yellow, turning blue where cut, (Smith), pores bruise dark inky blue (Siegel)

Stem:
4-10cm x 1-2cm, cylindric to club-shaped, "reddish or with red longitudinal striations over a yellowish base when young, soon becoming brownish to reddish brown over much of the stipe to extensively brown with a red band at apex", (Frank(9)), 4.5-10cm x 1-2cm, nearly equal, solid; "with a pale tan to olive-buff or whitish ground color that is typically punctate with reddish dots and points"; dry, not reticulate; yellow basal mycelium, (Bessette), 4-9cm x 1-1.5(2)cm, equal; reddish in a few places but usually entirely olive gray to the pallid apex; faintly pruinose and longitudinally striate at apex, (Smith), develops dingy brown tones (Siegel)

Chemical Reactions:
cap flesh no reaction to KOH or FeSO4 (Smith)

Odor:
indistinct, (Frank(9)), none (Smith)

Taste:
mild, (Frank(9)), mild (Smith)

Microscopic:
spores (11.4)13-16.2(18.1) x 5.2-6.5(7.1) microns, "fusoid to subcylindrical, inequilateral, most with truncate apex, smooth, weakly to distinctly amyloid", amyloid reaction of the spores "may fade over time or may be weak in some collections"; basidia (2)4-spored, 27.3-35.7 x 9.9-12.9 microns, clavate, colorless; hymenial cystidia 28.9-73.5 x 2.9-8.1 microns, "narrowly ventricose with elongated apices"; cap cuticle "a trichoderm made up of elongated cells" 8-10 microns wide, "with brown incrustations and pigment"; terminal cells conic; clamp connections absent, (Frank(9)), spores 13-18 x 4-7 microns, fusoid to subcylindric [spindle-shaped to somewhat cylindric], truncate, smooth, weakly to distinctly amyloid, ochraceous, (Bessette), spores 12-17 x 4.4-6 microns, "boletoid" in shape, smooth, "with a circular apical thickening depressed in the center and from here a discontinuity in the wall extends to the interior" (as in Boletus truncatus), on spores crushed out from the dried fruiting body weakly but distinctly amyloid (dull violaceous) and more violaceous in pore region than elsewhere, "spores from a deposit on clean white paper dextrinoid in outer half or one third (apical regions) and merely yellowish toward the apiculus"; basidia 4-spored, 32-38 x 8-10 microns, clavate, inamyloid; pleurocystidia scattered, 40-60 x 8-12 microns, narrowly fusoid to slightly ventricose to a subacute apex, not incrusted, colorless, thin-walled; cap cuticle a trichodermium of hyphae 8-15 microns wide, with plate-like incrustations of pale bister (in KOH) pigment along the walls, end-cell somewhat cystidioid; clamp connections rare, seen at base of occasional basidium in some fruitbodies, (Smith)

Spore Deposit:
"olive brown to dark reddish olive" (Frank(9)), dark reddish brown (Bessette), dark "wood brown" on white paper, (Smith)