Singerocomus inundabilis (Singer) T.W. Henkel in Henkel et al., Mycologia 108(1): 167 (2016)
Pileus 25–33(–47) mm broad, 6–9 mm tall, broadly convex to planate to slightly uplifted, occasionally with a low umbo when young, pinkish red (9A7– 10A7, 9B8–9C8) throughout, becoming lighter (9A6– 9B6) toward margin with age, under hand lens a dense tomentum of minute erect fascicles throughout, with age these separating to fine areoles toward margin exposing pale yellow ground; terminal elements of tomentum yellowish when young, dry to submoist; margin entire; trama 0.5–1 mm thick at margin, 2–4 mm over tubes, 4–5 mm above stipe, pale yellow with reddish band immediately beneath pileipellis, un‐ changing with exposure, reddening slightly around mycophagy damage, subsolid. Odor mildly fungoid; taste mild. Tubes 1–2 mm long at margin, 4–6 mm centrally, 1–2 mm at stipe, of slightly varying lengths, narrowly and deeply depressed at stipe, nearly free, with decurrent teeth 0.5–2 mm long, light yellow (2A4– 3A4), discoloring olivaceous (~3B7) with age, un‐ changing with exposure; edges concolorous, unchanging with pressure; pores subisodiametric to ovate and subangular, 1–2 per mm. Stipe 37–63(–70) 6 5– 7(–10) mm, subequal to subclavate, widening evenly toward base to 7–9 mm, attenuating slightly at extreme base, pinkish red (9A7–9B7) over upper two-thirds, lower third light yellow (2A5–3A5), glabrous, slightly pulverulent and faintly longitudinally striate under hand lens; basal mycelium a low, light yellow tomentum descending into soil, with concolorous hyphal cords; trama light yellow (~ 2A6) throughout, unchanging, solid.
Basidiospores dark olivaceous brown (5E7–5F7) in heavy deposit, 6–9 6 4–5.5(–7) μm, Q range 1.2–1.8 (–2.0) (mean Q = 1.38), ellipsoidal, with prominent suprahilar depression, olivaceous brown in H2O and KOH, mostly uniguttulate, inamyloid, smooth; hilar appendage prominent, 0.5–1 μm long; wall 0.5 μm wide; surface under SEM smooth. Basidia (20–)25–35 (–42) x (7–)8–10(–12) μm, clavate to broadly clavate, tapering evenly downward, hyaline in KOH and H2O, devoid of refractive content or variously granulose-guttulate; sterigmata 2–6 μm long, two, three, or four per basidium. Pleurocystidia infrequent, (28.5–) 34.5–61 (–74) x 7.5–10 μm, narrowly to broadly ventricoserostrate, projecting 12.5–29.5(–42) μm above hymenial palisade, thin-walled, devoid of refractive contents. Cheilocystidia absent. Hymenophoral trama phylloporoid, subparallel, non-gelatinized, in mass pale yellow-gray in H2O, paler in KOH; individual hyphae somewhat inflated, 3.5–10 μm wide, with lightly pigmented walls and faint transverse bands; mediostratum indistinct; conductive hyphae absent. Pileipellis a trichodermium of filiform elements, in mass grayish orange-brown in H2O, lighter in KOH; individual hyphae frequently septate and projecting at irregular lengths, 4–8 cells per filament, uniformly pale orange-gray in H2O, faint yellow-gray in KOH; terminal cells (17–)20–49(–61) x (3.5–)5–10(–12.5) μm, cylindrical with rounded tips, rarely subclavate, pale yellow in H2O and KOH; walls smooth, not incrusted; subterminal cells close-septate, longer septate at deeper levels, inflating at varying degrees and occasionally with bifurcate branching patterns; walls with scattered, irregular flake-like incrustations. Pileus trama a compact mass of partially gelatinized hyphae, in mass grayish to orange-yellow in H2O, paler in KOH; individual hyphae slightly inflated, 3.5–12.5 μm wide, with scattered minute flake-like external incrustations and faint transverse bands; conductive hyphae absent. Stipitipellis a shallow trichodermial palisade, in mass pale orangish gray in H2O, pale gray in KOH; terminal cells ventricose, ventricose-rostrate, clavate, cylindrical, or occasionally ovate, 24.5–49.5(–54.5) x (5–)7.5–12.5 μm. Stipe trama of loosely packed, slightly inflated hyphae, in mass orangish gray in H2O, lighter in KOH; individual hyphae 3.5–7.5 μm wide; walls with brownish flake-like incrustations; contents faint gray, granulose. Clamp connections absent. Macrochemical reactions: 10% NH4OH and 3% KOH slightly yellowing on pileus, unreactive elsewhere.
Habit, habitat and distribution: Solitary to scattered on litter fragments on the forest floor in seasonally inundated igapo forest with ECM Aldina trees, and on humic deposits of the forest floor and pseudotrunks of D. corymbosa on upland lateritic and white sand soils. Known from the type locality in the central Brazilian Amazon, the Upper Potaro River Basin of Guyana and from the Upper Mazaruni Basin based on a DNA sequence from ECM roots.
Index Fungorum number: IF 811839
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.