Russula pakaraimaeae S. L. Mill. & T. W. Henkel 2024, sp. nov.
Creators: name: Miller, Steven L.
name: Aime, M. Catherine
name: Henkel, Terry W.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Fungi
Basidiomycota
Agaricomycetes
Russulales
Russulaceae
Russula
Russula pakaraimaeae

description: Russula pakaraimaeae S.L. Mill. & T.W. Henkel sp. nov. (Fig 4)
Mycobank: 854654.
Diagnosis: Russula pakaraimaeae is characterized by its small stature (pileus 5–17 (25) mm), its occurrence in the Upper Mazaruni Basin of Guyana in fringe forests surrounding the Pegaima savanna in association with Pakaraimaea dipterocarpaceae and possibly Dicymbe jenmanii, by its fruiting habit with branching or single rhizoidal base attached to large fallen leaves and organic debris, by its dark red to brownish violet pileus with pruinose white margin when young, stipe viscid in wet conditions wet then with appressed fibrillose squamules often flushed pinkish when conditions are dry, spores of isolated verrucae with no interconnections and a distinct suprahilar plage that occasionally forms a partial collar on the apiculus, by its long hairlike pileocystidia arising from scattered swollen cells.
Etymology: in reference to the occurrence in forests fringing savanna dominated by Pakaraimaea dipterocarpacea (Cistaceae).
Holotype: GUYANA. Pakaraima Mountains, Upper Mazaruni River Basin, fringing forest around the Pegaima savanna, 0.5 km S of Pegaima base camp located at 5° 26′ 21.3′′ N; 60° 04′ 43.1″ W, ~ 800 m elevation; under Pakaraimaea dipterocarpacea and Dicymbe jenmanii, 21 December 2010, T.W. Henkel 9503 (holotype BRG; isotypes HSCF 004453, RMS). GenBank ITS KC155378.
Macroscopic description:— Pileus 5–17(25) mm broad, first convex and sometimes mammilate, then broadly convex to slightly depressed, with or without umbo; margin decurved, entire but markedly pruinose when young, then frequently minutely lacerate or crenulate with age, smooth to obscurely striate when young, faintly plicate to subsulcate when older, striations 2–4 mm in length; pellis dull to shiny, heavily pruinose when young especially toward the margin, viscid when wet, subfloccose to subtomentose when dry, matted toward the margin, dark red (11C6–11C7) to brownish violet (11D7–8) to violet brown (11F7–8) with extreme margin white when young, then red to dark red or brownish red(10B7–10D7,8) when expanded, disk and umbo remaining violet brown (11E6–11F8). Lamellae 1–2 mm broad at mid-radius, adnate to slightly sinuate to subdecurrent, close to subdistant, entire, white when young, eventually pale yellow (3A 2–3); lamellulae rare to absent. Stipe 14–33 (48) × 1.5–3 (5) mm, equal or more typically tapered to single or branching rhizoid-like base, attachment central, even to slightly irregular, flattening, canaliculate with age, pruinose above, middle portions with white to pink appressed fibrillose squamules, base subtomentose, white to cream (3A 2–3) at apex (i.e. concolorous with lamellae, middle portions overlain with pale red areolae frequently in a stretch-mark like pattern over a white or yellowish white (3A2) ground; the base concolorous with the apex; viscid in wet conditions. Context in pileus 1–1.5 mm at mid-radius pliant, white, pale pink immediately below cuticle, especially at disk; trama in stipe stuffed at maturity, outer cylinder pale yellow surrounding white central core; odor mild; taste mild to faintly sweet or slightly bitter; FeSO4 not noted.
Microscopic description:— Basidiospores 7.2–8.8 × 5.8–7.04 (x= 7.96 × 6.4, Q = 1.25–1.3, Qm=1.25), broadly ellipsoid; ornamentation of widely distributed, isolated, acute, narrowly conical elements, 1.5–2(–2.5) μm high, amyloid, darkest near the apiculus; suprahilar plage large and verruculose, not or forming a collar on the apiculus. Basidia 25–3 × 8–10 μm, subcylindrical to clavate, 4-spored, sterigmata long, 6.4–10 × 1.5–1.9 μm. Hymenial cystidia 35–50 × 6–8 μm, cylindrical, subclavate to clavate, obtuse to capitate, or occasionally rostrate, mostly thin-walled, some thick-walled, some long, arising deep within the lamella trama, others shorter arising in hymenium, emergent 2–40 μm above basidia, scattered to numerous 800-1000 per mm 2, SV–. Marginal cells 45–75 × 7–13 μm, subclavate, fusiform, mucronate or irregular, strongly emergent, mixing with small basidia, moderately numerous. Subhymenium well developed of small tightly packed spherical cells of 10 μm diam. Lamellar trama composed of many large sphaerocytes,and nests of relatively small, nearly isodiametrical to globose sphaerocytes, interwoven with cylindrical hyphae. Pileipellis, two-layered; subpellis of slightly interwoven inflated to swollen hyphae of 6–15μm diam; suprapellis arranged in a loose trichoderm from pileus center to pileus margin composed of infrequently branching spindly hyphae, 5–12 μm diam, cylindrical to clavate or digitate, obtuse or sinuous and irregularly constricted, often multi-septate, thin- or thick-walled, often arising from inflated cells; Pileocystidia 50–250 μm × 3–5 µm obtuse digitate or capitate, pedicellate, septate, irregularly constricted or swollen at the septum, banded with refringent contents particularly near the septa, thin-or thick-walled, arising deep in the trama but extending 120–160 µm above the surface of the pellis, these easily disarticulated in microscopic preparations, SV- to pale grey, orthochromatic in Cresyl Blue, the contents or interior of the walls acid resistant in BF, no incrustations were observed. Stipitipellis resembling the pileipellis, composed of branching, septate, irregularly shaped hyphae that taper at the apex, and long pedicellate, septate, thick-walled caulocystidia that are cylindrical, digitate, clavate, obtuse or capitate and irregularly constricted 50–250 µm.
Habit, habitat, and distribution:—Solitary or in small troops in December on humic matter and large fallen leaves on forest floor in ECM P. dipterocarpacea / Dicymbe jenmanii savanna fringing forests, or in stands with only P. dipterocarpacea. Sequences corresponding to R. pakaraimaeae have also been found from the sampling of ectomycorrhizal roots at the Pegaima savanna (Smith et al. 2013). Known only from the type locality in the Upper Mazaruni Basin of Guyana.
Additional specimens examined:— GUYANA. Pakaraima Mountains, Upper Mazaruni River Basin, fringing forest around the Pegaima savanna, within a 1.5 km radius of Pegaima base camp located at 5° 26′ 21.3′′ N; 60° 04′ 43.1″ W, ~ 800 m elevation; 0.1 km N of base camp in pure stand of Pakaraimaea dipterocarpacea, 22 December 2010, T. W. Henkel 9515 (BRG; HSCF 004454; RMS); 1.5 km SW of base camp in pure stand of Pakaraimaea dipterocarpacea, 26 December 2010, T. W. Henkel 9548 (BRG; HSCF 004455; RMS).
description: Published as part of Miller, Steven L., Aime, M. Catherine & Henkel, Terry W., 2024, Russulaceae of the Pakaraima Mountains of Guyana 5. Two newly described diminutive species in a novel lineage of the crown clade of Russula (Russulaceae), pp. 117-129 in Phytotaxa 668 (2) on pages 123-125, DOI: 10.11646/phytotaxa.668.2.1, http://zenodo.org/record/14520299