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Page number:423 
Remarks (internal):Xerocomus cyaneibrunnescens is a distinctive bolete recognized in the field by its consistently rugose, ochraceous brown pileus becoming finely areolate to rivulose with age, bluish cream hymenophore staining from brown to blue to dark brown, tan, subequal, apically reticulate stipe with a distinctive greenish to bluish band at the apex in fresh specimens, and habit of fruiting from accumulated humic materials on or around trunks of large Dicymbe trees. The species is best disposed in Xerocomus s.l. based on the morphological features of hymenophoral tubes that are sublamellate near the stipe and adnate with large, subangular pores, subequal stipe, parallel tube trama, and trichodermioid, dry pileipellis (Singer 1986). While the reddish brown basidiospore deposit is unusual, it has been recorded in other xerocomoid species with parallel tube trama (e.g. Xerocomus ferruginosporus [Corner] E. Horak).
Xerocomus cyaneibrunnescens was determined by Smith et al. (2011) to form ectomycorrhizas with the leguminous hosts D. corymbosa, D. altsonii and A. insignis and ranked 31st in frequency out of 118 ECM fungal species recovered using molecular methods from 1140 root tips sampled from 57 trees in the Upper Potaro Basin. Infrequent fruiting of X. cyaneibrunnescens in Guyana’s Dicymbe forests was recorded in a long-term D. corymbosa plot study of Henkel et al. (2012), with its basidiomata occurring in 3.3% of 630 quadrats sampled during the May-Jul rainy seasons over 7 y. Ectomycorrhizas of X. cyaneibrunnescens/D. corymbosa are illustrated (Fig. 4).
Among Xerocomus species described by Singer from the Brazilian Amazon, X. globuliger Singer is similar to X. cyaneibrunnescens in its brownish, dry, rugose pileus, parallel hymenophoral trama lacking a distinct mediostratum, ventricose-rostrate pleurocystidia, lack of a distinct bluing reaction of the pileipellis with ammonia, and association with leguminous host plants (Singer et al. 1983). Xerocomus globuliger can be distinguished from X. cyaneibrunnescens by its yellow, unchanging tubes, lack of a stipe reticulum, regularly four-sterigmate basidia, much longer basidiospores (13-17.5 vs. 10-11 µm) that are olivaceous brown and lack of incrusted pileipellis hyphae. Xerocomus scrobiculatus Singer resembles X. cyaneibrunnescens in its dry, pallid brownish pileus, which lacks a distinct bluing reaction to ammonia, low stipe reticulum, similarly sized basidiospores, hyaline, parallel hymenophoral trama with indistinct mediostratum, and association with leguminous host plants, but differs in its citron yellow tubes, scrobiculate pileus, lack of auto-oxidation reaction of the bruised tubes or exposed trama, presence of a mucronate apex on the olivaceous brown basidiospores, and lack of incrusted pileipellis hyphae (Singer et al. 1983).
Among Malaysian xerocomoid boletes combining the features of X. cyaneibrunnescens of dry, dull brown pilei, a weakly reticulate stipe, cyanescent or brunnescent bruising reaction on the tubes, more or less cylindrical pileipellis elements and broadly fusiform basidiospores lacking in olivaceous tones, X. lucescens (Corner) E. Horak differs from X. cyaneibrunnescens in its more reddish brown pileus, lack of green to bluish coloration in the fresh tubes and stipe apex, persistently cyanescent bruising reaction, presence of cheilocystidia, and regularly cylindrical pileipellis terminal cells (Corner 1972, Horak 2011). Xerocomus pseudochrysenteron (Corner) E. Horak differs from X. cyaneibrunnescens in its adnate to subdecurrent tubes, reddish brown lower stipe, a more dramatic and intense bluing reaction on the tubes and exposed trama lacking a brunnescent phase, presence of cheilocystidia, and pale brown as opposed to red brown basidiospores. Xerocomus ferruginosporus (Corner) E. Horak is one of the few Malaysian taxa with reddish brown basidiospores but differs fundamentally from X. cyaneibrunnescens in its much longer, slender fusoid basidiospores (16.5-20 vs. 10-11 µm), white to pale brown tubes with much smaller pores, lack of cyanescent or brunnescent bruising reactions and lack of a distinct stipe reticulation.
The Congolian X. sulcatipes Heinem. & Gooss.-Font. is remarkably similar to X. cyaneibrunnescens in the combination of ochraceous, rugose-tomentose pileus becoming areolate toward the margin, grayish green, non-decurrent tubes, yellowish tan stipe with a grayish green apex, cyanescent reaction of the exposed trama, and similarly shaped pleurocystidia, basidia and pileipellis terminal cells. Xerocomus sulcatipes can be separated from X. cyaneibrunnescens by its longer (12-14.7 vs. 10-11 µm), more fusiform, brown basidiospores, more strongly inflated pileipellis terminal cells (10-20 vs. 4.9-10 µm wide), yellowish stipe with a reddish base, and lack of an auto-oxidation reaction of the bruised hymenophore (Heinemann and Goossens-Fontana 1954).
 
Description type:Original description 
Description:Xerocomus cyaneibrunnescens T.W. Henkel et Husbands, sp. nov. Figs. 1-3
MycoBank MB564750
Pileus 30-62(80) mm broad, 8-30 mm tall, convex to broadly convex to plano-convex, tannish brown (5C3-5C5) throughout when young, darkening slightly (6D3-D5) with age, sometimes with darker brown discolorations, evenly rugose throughout, rugosities broadening and becoming more regular with age, surface under hand lens an erect tomentose mat throughout, with age separating to finely areolate or rivulose toward margin revealing light tan ground, rarely extending over the disk, dry; margin entire with a narrow tan tissue flap; trama subsolid, 1-2 mm at margin, 4-12 mm over tubes, 5-18 mm over stipe, initially off-white, bluing slowly but distinctly especially in older specimens, larval channels brown. Odor mild, boletoid; flavor pleasantly fungoid. Tubes 1-4 mm at margin, 3-10 mm centrally, 2-6 mm at stipe, occasionally sublamellate near stipe, narrowly depressed around stipe, initially cream (3B3-4B3) to light greenish cream (1B3-1C3) or rarely livid light grayish green (29D4, 30C4), maturing darker concolorous and then brownish (4C4-4D4-5D4), staining instantly brown under pressure, becoming distinctively bluish brown within 60 s, eventually to dark brown (~ 6F5-F8); tube edges concolorous, finely roughened under hand lens; pores somewhat stuffed when young, otherwise 1 per mm, initially subisodiametric, subangular at maturity. Stipe 45-107 mm x 5-17 mm, subequal, broadening slightly at base to 9-19 mm, sometimes flaring outward at extreme apex, usually curved, dull tan (5B3-5B4) over upper three-fourths, discoloring brownish where handled, usually with a narrow, well demarcated band that is light grayish green (~1C2) to light grayish turquoise (~ 25C3) to rarely brilliant aquamarine blue (24 A3-A4-B4) near extreme apex, 1-1.5 mm wide, with age bluish band becoming progressively darker reddish brown, sometimes subtended by a more reddish zone; upper one-third to two-thirds with distinct low concolorous reticulum more pronounced in mature basidiomata, reticulations discoloring brownish with handling, lower quarter with fine whitish tomentum on tan ground, this coalescing downward into a white, densely matted basal mycelium; trama off-white throughout, fibrous, slowly bluing in older specimens, subsolid.
Basidiospores dark reddish brown (7F7, 8F6-F8) in medium deposit, (9)10-11(13) x 4.5-5(6) µm, Q range (1.8)2-2.5(3) (mean Q = 2.2), broadly subfusiform, smooth, with a shallow suprahilar depression, reddish brown in H2O, lighter in KOH, inamyloid, uni- to multiguttulate; hilar appendage 0.4-0.5 µm long; wall 0.3-0.5 µm thick; surface under SEM with extremely minute, low ridges, but not distinctly bacilliform. Basidia (22.2)29.6-39.5(46.9) x 7.4-9.9 (12.4) µm, clavate or infrequently narrowly clavate, tapering evenly toward base, hyaline in H2O and KOH, devoid of refractive content or occasionally granulose and guttulate, these contents olivaceous brown in H2O, pale gray in KOH; sterigmata (1.2)2.5-2.7(4.9) µm long, two, three or four per basidium. Pleurocystidia infrequent, (34.6)37.1-61.8(76.6) x (7.4)9.9-14.8(17.7) µm, ventricose to ventricose-rostrate to clavate-mucronoid, evenly embedded within or extending 10-22 µm above the hymenial palisade, devoid of contents to occasionally with light gray cytoplasm in KOH, pigment more obvious in H2O. Cheilocystidia absent. Hymenophoral trama phylloporoid, parallel to barely diverging, in mass olivaceous gray in H2O, hyaline to faintly yellow in KOH, mediostratum indistinct; hyphae 4.9-7.4(9.8) µm wide, hyaline in H2O and KOH, slightly gelatinized in older specimens; conductive hyphae scattered throughout, these 4.9-12.3 µm wide, with opaque, hyaline to pale orange, guttulate cytoplasm. Pileipellis a trichodermial palisade of cylindrical to variously inflated, close-septate hyphae with rounded tips projecting at slightly irregular lengths, often with minute granular external incrustations in faint band-like patterns, granulose-guttulate, in mass orangish brown in H2O, lighter in KOH, occasionally with short branches from penultimate cells; terminal cells 18.5-37.1(49.4) x (3.7)4.9-10(12.4) µm, cylindrical, obclavate, or subutriform, frequently with irregular nodulose projections; subpellis dense, tannish yellow in KOH. Pileus trama densely interwoven; individual hyphae hyaline, thin walled, devoid of obvious contents, curving and much branched, 4.9-9.9 µm wide, interspersed with frequent opaque, hyaline conductive hyphae, these more concentrated near subpellis. Stipitipellis a trichodermium; terminal elements ventricose, clavate, subglobose, or lageniform, (17.3)24.7-74.1(98.8) x 7.4-19.8(24.7) µm, thin-walled, with pale grayish yellow cytoplasmic contents in KOH, darker in H2O, occasionally guttulate. Stipe trama in mass with orangish yellow cytoplasmic pigmentation in H2O, lighter in KOH; individual hyphae 4.9-8.6 µm wide. Clamp connections absent. Macrochemical reactions: 10% NH4OH yellowish olive on pileus and stipe trama, dark brown instantly on stipe base; 3% KOH dark brown over 30 s on pileus, stipe base, and lower stipe trama, light reddish brown on pileus trama.
Holotype: Henkel 9197 (BRG; ISOTYPE HSU; NY).
Habit, habitat and distribution: Solitary or scattered around the base and on humic deposits on trunks of D. corymbosa trees on lateritic soils; also found in association with D. altsonii on sand soils; known from the type locality in the central Pakaraima Mountains and ~ 100 km to the east near Mabura Hill in the lowlands of Guyana.
Specimens examined: Guyana. Region 8 Potaro-Siparuni: Pakaraima Mountains, Upper Potaro River Basin, 2 km southeast of base camp near Dicymbe plot 1, 17 May 2010, Henkel 9197 (Holotype BRG; Isotypes HSU, NY), GenBank ITS/LSU: JQ751259;
 
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