Binderoboletus segoi T.W. Henkel & Husbands, in Henkel et al., Mycologia 108(1): 159 (2016)
Etymology: In honor of Francino “Sego” Edmund, Patamona Amerindian field assistant and collector of the type specimen.
Diagnosis: Pileus olive-yellow to olive-brown, matted fibrillose, with age finely subareolate, subviscid, glossy when dry, trama light yellow, unchanging. Hymenophore tubulose, adnate, sublamellate at stipe, light yellow, browning with pressure, pores subisodiametric, 1–2 per mm. Stipe subequal, concolorous and longitudinally striate over lower one-half, yellowing and reticulate over upper one-half, base yellow tomentose with concolorous hyphal cords, trama bright yellow. Basidiospores olivaceous brown in deposit, smooth, subfusiform, mean Q 5 2.2, dextrinoid in Melzer’s reagent. Basidia narrowly clavate to clavate, sterigmata mostly two or four. Pleurocystidia narrowly ventricose to ventricoserostrate, contents dextrinoid in Melzer’s reagent. Cheilocystidia few. Hymenophoral trama parallel to slightly divergent (phylloporoid), mediostratum indistinct. Pileipellis an entangled cutis, hyphae externally incrusted, terminal cells cylindrical. Stipitipellis hymenidermous. Clamp connections absent. NH4OH slightly orange-brown on pileus, stipe and trama.
Pileus (35–)60–90(–135) mm broad, 15–35 mm tall, broadly convex, occasionally plano-convex, dark olive yellow initially (3D8–3E8), with more olive-brown (4D8–4E8) patches at maturity; surface initially densely matted fibrillose and occasionally rugulose, with age finely subareolate revealing yellow ground, moist to viscid when wet, with a distinct glossy sheen in dry conditions; margin entire; trama 1–3 mm thick at margin, 9– 17 mm over tubes, light yellow (2A3–2A4), solid, unchanging. Odor mildly fragrant; taste mild to slightly sour. Tubes 1–3 mm long at margin, 4–9 mm centrally, 3–5 mm at stipe, sublamellate immediately near stipe, adnate and contiguous with upper stipe reticulum, light yellow (2A5–2B5), browning slightly when cut; tube edges concolorous, browning (5E5– 5F5) quickly under pressure; pores subisodiametric, 1–2 per mm. Stipe (36–)52–80(–98) 6 11–25 mm, subequal, broadening slightly over basal one-fifth to 15–32 mm, concolorous with pileus and longitudinally striate over lower one-half, striations anastomosing upward into a true reticulum toward apex and there grading to grayish yellow (2B6–2B7) to yellow (2A6–2A7) at apex; apical reticulations tall, nearly lacunose, browning with pressure; trama bright yellow (2A8) throughout, orangish brown around larval channels, solid, unchanging to slightly browning; basal mycelium a bright yellow tomentum, subtended by abundant concolorous hyphal cords.
Basidiospores olivaceous brown (5E6–5F6) in heavy deposit, (8–)9–12(–14) x (3–)4–5(–6) μm, Q range = (1.8–)2.0–2.4(–2.8) (mean Q = 2.2), subfusiform, smooth, with a broad, shallow suprahilar depression, pale olivaceous brown in H2O and KOH, uniformly dextrinoid to orangish to reddish brown in Melzer’s, uni- to multiguttulate; hilar appendage 0.5– 1 μm long; wall 0.4–0.5 μm thick; surface under SEM slightly undulating, otherwise smooth. Basidia (17–) 24–35(–40) 6 (7–)8–10(–11.1) μm, narrowly clavate to clavate, tapering evenly toward base, hyaline in H2O and KOH, devoid of content or cytoplasmically dense with greenish yellow granules and globules in KOH, these paler in H2O; sterigmata 3–7(–8) μm long, two, four, or occasionally three per basidium. Pleurocystidia frequent, (15–) 27– 49.5(–69) 6 (5–)6– 10(–12.5) μm, narrowly ventricose to ventricoserostrate, subacuminate at apex, barely projecting above hymenium to 5–15 μm, with 1–2 large ochraceous, amorphous globules in the ventricose portion in otherwise hyaline epiplasm in H2O and KOH, these globules uniformly dextrinoid to dark orangish to reddish brown in Melzer’s, rarely distributed throughout. Cheilocystidia few, (19.5–) 24.5–30(–32) 6 5–7.5 μm, narrowly ventricose-rostrate, devoid of cytoplasmic contents or with 1–2 large olive-yellow globules in KOH, barely projecting above tube edge. Hymenophoral trama phylloporoid, parallel to slightly diverg‐ ing, in mass light yellow-gray in H2O, paler in KOH; hyphae somewhat inflated, 5–10(–12.5) mm wide, with uniformly faint gray cytoplasmic pigmentation in H2O and KOH; mediostratum indistinct; conductive hyphae frequent, opaque, irregularly branched, 2.5–5 mm wide. Pileipellis a cutis of periclinal to subanticlinal, uninflated, highly entangled hyphae, in mass rich brownish yellow in H2O, light yellow-gray in KOH; individual hyphae with scattered, irregular clump-like external incrustations, these 0.5–1 mm tall, occasionally with short side branches or nodules on subterminal cells, faint gray in KOH; terminal cells uninflated, cylindrical with rounded tips, (25–)27–62(–79) 6 2.5–5(–6) μm. Pileus trama interwoven, in mass light brownish yellow in H2O, faint yellow-gray in KOH; individual hyphae thin-walled, nearly hyaline, slightly inflating, (4–)5–10 (–12.5) μm wide; conductive hyphae scattered, opaque, 2.5–3.5 μm wide. Stipitipellis hymenidermous, in mass olivaceous orange in H2O, pale olivaceous yellow-gray in KOH; sterile terminal elements ventricose-rostrate, clavate, or cylindrical, (17.5–)24.5–49.5 6 (5–)7.5–10 μm, interspersed in the grooves of the reticulum with numerous subcylindrical basidia bearing basidiospores, these more frequent over upper half of the stipe; penultimate cells anticlinal, irregularly branched, with externally incrusted walls. Stipe trama densely packed, in mass olive-yellow in H2O, faint yellow-gray in KOH; individual hyphae somewhat inflated, 3.5–10(–12.5) μm wide, hyaline, with irregularly clumped, opaque external incrustations; conductive hyphae scattered throughout, opaque, hyaline, irregularly branched. Clamp connections absent. Macrochemical reactions: 10% NH4OH slightly orange-brown on pileus, stipe, and trama; 3% KOH burgundy on pileus.
Habit, habitat and distribution: Solitary to scattered on humic mat of the forest floor in monodominant D. corymbosa stands or mixed D. corymbosa, D. altsonii and A. insignis stands on lateritic soils; also found in D. altsonii monodominant stands on white-sand soils; known from the type locality in Guyana’s Upper Potaro River Basin and ~ 100 km to the east in the Upper Demerara River Basin.
Figure 1: Maximum likelihood phylogram (−ln 36456.292067) based on 28S ribosomal DNA and RPB1 sequences depictin phylogenetic relationships of the new Guyanese bolete taxa Binderoboletus segoi, Guyanaporus albipodus, Singerocomus inundabilis and Singerocomus rubriflavus within the Boletaceae. Support values above the nodes are maximum likelihood bootstrap support values. Nodes with bootstrap support values , 75 are not shown. Clades with multiple species from the same genus are collapsed into triangles for visual simplification as is a clade of outgroup taxa from other suborders or families of Boletales.