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Russula lentiginosa Buyck & Mitchell

Macroscopic features:

Pileus (2.7-) 4-8.5 (-11) cm diam., shape regular in outline, broadly convex to plane, then somewhat depressed or rarely funnel-shaped in age; margin plane to slightly incurved, obscurely striate for 2-5 (-13) mm, separable for 1/3-1/2 of the radius, dull or slightly shiny, deep red (9-10BCD6-8) with the center typically very dark, nearly black, sometimes discolored and more yellowish brown, with a very dense ochre, floccose to granular covering, particularly in the center of young specimens, more diffuse with age; trama (2-) 3-5 (-6) mm at mid-radius, firm, white, pink under the cuticle, unchanging when cut but slowly browning with age or from insect damage.
Gills adnate, adnexed, or slightly decurrent, close to sub-distant with few lamellulae of varying length, not strongly narrowing towards the pileus margin, hardly to moderately forking near the stipe and occasionally elsewhere, 3-5 (-8) mm high at mid-radius, cream to whitish, brownish where insect damaged; edge entire, concolorous.
Stipe central to slightly eccentric, usually not exceeding pileus diam. in length, 3-9 x 1.2-2 (-2.7) cm, equal to subclavate or tapering towards the base, white to cream and with ochre to brownish scales or floccules toward the base, velvety elsewhere, firm; trama stuffed, very slowly browning when exposed.
Chemical reactions: stipe trama salmon to pink with FeSO4.
Taste quickly and strongly acrid in gills, almost mild to tardily or moderately acrid in cap trama. Smell not distinctive.
Spore print whitish (between Romagnesi code I(a)b, Dagron code 3).
Exsiccatum retaining the pigmentation of the cap of the fresh fungus without much alteration.

Microscopic features:

Spores ellipsoid, (7.3-) 7.8-8.30-8.8 (-9.4) x (6.2-) 6.4-6.71-7.0 (-7.6) µm (Q = 1.12-1.24-1.36); ornamentation dense, composed of many, blunt, distinctly amyloid warts, up to 1 µm high, mostly interconnected with very fine lines, sometimes catenulated, resulting in a dense, complete to incomplete reticulum; suprahilar spot large, graying in Melzer's reagent.
Basidia 27-38 x 10-12 µm, short and distinctly clavate, four-spored; sterigmata stout, 5-8 x 1.5 µm.
Hymenial cystidia both on edge and sides of the gills, moderately numerous (pleurocystidia 1200-1500/mm²), slender and quite short, hardly emerging beyond the hymenium level, originating mostly in the subhymenium, sometimes from within the lamellar trama and then up to 140 µm long, fusiform to clavate, mostly appendiculate, 51-69 x 7-9 µm, thin-walled; contents abundant, crystalline, turning black with SV.
Marginal cells not differentiated. Subhymenium relatively large-celled.
Lamellar trama mainly composed of sphaerocytes intermixed with abundant, slender, cylindrical, mostly unbranched, cystidioid elements up to 5 µm diam., not breaking up easily when squashed.
Pileipellis orthochromatic in cresyl blue with very distinct pigment-incrusted hyphae on top of the gelified pellis, obscurely two-layered; subpellis hyphae mostly 2-4 µm wide, often irregularly sinuose or inflated, thin-walled, slightly separated by gelification, forming a loose tissue; suprapellis a dense trichodermal layer of more or less gelified, sinuous, irregular endings of the subpellis-hyphae and long, cylindrical and slender, sparsely septate extremities with yellowish brown incrusted walls and refringent contents, at least towards the apical cells, these generally lying dispersed or aggregated in tufts on top of the smaller elements, only 2-4 (-6) µm wide but up to several hundred µm long, rounded at the apex, rarely moniliform or capitate. Pileocystidia in suprapellis not observed, present and abundant in subpellis and continuing as 'lactifer'-like hyphae in trama underneath, with coarsely granular to crystalline contents.
Stipitipellis lacking any particular structure, composed of undifferentiated endings of hyphae encrusted with a yellowish brown pigment near the base and abundant cylindrical caulocystidia.
Clamps absent.

Ecology:

Mostly scattered among forest litter in broadleaf or mixed broadleaf/Tsuga canadensis woods.

Nomenclature

Photographs

Microscopy

SEM photos