Russula acrialbida Manz, F. Hampe & Yorou 2025, sp. nov.

Russula acrialbida Manz, F. Hampe & Yorou, sp. nov. Figs 4, 5, 6 Holotype. Benin. Collines, Toui, Forêt de Toui-Kilibo, co-ord. 8°36.4'N, 2°38.0'E, alt. 340 m, Sudanian woodland, under Isoberlinia doka, on sandy soil, 06. 07. 2021, leg. C. Manz, F. Hampe, N. S. Yorou & G. Abohoumbo, CM-21-093 (holotype B 70 0105401, isotype UNIPAR). Additional material examined. Benin. Borgou, Wari-Maro, Forêt de Wari-Maro, co-ord. 9°11.1'N, 2°12.8'E, alt. 280 m, Sudanian woodland, under I. doka, on sandy soil, 30.06 2021, leg. C. Manz, F. Hampe, D. Dongnima & S. Badou, CM-21-038 (paratype, B 70 0105402, UNIPAR); ibid. co-ord. 9°07.9'N, 2°07.5'E, alt. 340 m, Sudanian woodland, under I. doka, on sandy soil, 30.06 2021, leg. C. Manz, F. Hampe, D. Dongnima & S. Badou, CM-21-039 (paratype, B 70 0105403, UNIPAR); ibid. CM-21-041 (paratype, B 70 0105404, UNIPAR); ibid. co-ord. 9°11.0'N, 2°12.8'E, alt. 310 m, Sudanian woodland, under I. doka, on sandy soil, 25. 06. 2022, leg. C. Manz, F. Hampe, S. Sarawi, A. Rühl & D. Dongnima, CM-22-215 (paratype, B 70 0105405, UNIPAR); ibid. N’dail, Forêt de N’Dali, co-ord. 9°45.4'N, 2°40.1'E, alt. 360 m, Sudanian woodland, under I. doka, on sandy soil, 01. 07. 2021, leg. C. Manz, F. Hampe & G. Abohoumbo, CM-21-049 (paratype, B 70 0105406, UNIPAR); ibid. Kpéssou, Forêt de l’Ouémé Supérieur, co-ord. 09°15.8'N, 002°11.1'E, alt. 330 m, Sudanian woodland, under I. doka, on sandy soil, 02. 07. 2021, leg. C. Manz, F. Hampe, N. S. Yorou & G. Abohoumbo, CM-21-053 (paratype, B 70 0105407, UNIPAR); ibid. CM-21-054 (paratype, B 70 0105408, UNIPAR); ibid. CM-21-062 (paratype, B 70 0105409, UNIPAR); ibid. co-ord. 9°45.6'N, 2°8.0'E, alt. 320 m, Sudanian woodland, under I. doka, Isoberlinia tomentosa & Uapaca togoensis, 18. 07. 2021, leg. C. Manz, F. Hampe, N. S. Yorou & G. Abohoumbo, CM-21-138 (paratype, B 70 0105410, UNIPAR); ibid. Collines, Toui, Forêt de Toui, co-ord. 8°37.7'N, 2°35.6'E, alt. 320 m, Sudanian woodland, under I. doka, on sandy soil, 05. 07. 2021, leg. C. Manz, F. Hampe, N. S. Yorou & I. Oguchina, CM-21-083 (paratype, B 70 0105411, UNIPAR); ibid. Atakora, Natitingou, Kota waterfalls, co-ord. 10°12.7'N, 1°26.6'E, alt. 500 m, Sudanian woodland, under I. tomentosa, on rocky soil, 15. 06. 2022, leg. C. Manz, F. Hampe, S. Sarawi, A. Rühl & D. Dongnima, CM-22-175 (paratype, B 70 0105412, UNIPAR). Diagnosis. One of the most common Russula species in Sudanian woodlands in Benin, characterised by large white basidiomata, pileus surface with fine cream-coloured patches, burning acrid taste, small spores with a nearly smooth surface, a trichodermal pileipellis with attenuated hyphal terminations embedded in a gelatinous matrix and cystidia rapidly staining black in sulphovanillin, occurring in savannah woodlands. Differs from R. roseovelata by the absence of large detaching areolae on the pileus surface. Description. Growth habit: basidiomata solitary or in groups of up to ten. Pileus: mostly large to very large, rarely medium-sized, 35–155 mm in diam., when young, hemispherical, apically truncated or sometimes even slightly depressed, with margins touching the stipe, in shape similar to a matchstick head, later expanding plane, centrally depressed; margin involuted and slightly remaining so even when mature, distinctly tuberculate-striate up to 10–15 mm, frequently radially cracked, regular or slightly undulate; cuticle smooth, dry or slightly greasy when wet, finely areolate, patched towards the pileus margin, peelable up to 1 / 2 – 3 / 4 of the pileus radius, colour white, yellowish-white (4 A 2), ivory (4 B 2) or cream (4 A 3), rarely with a faint pinkish-white (9 A 2) hue, near the centre also orange-white (5 A 2), patches near the margin grey orange (5 B 4-5), apricot yellow (5 B 6), pompeian yellow (5 C 6), cocoa brown (6 E 6), cognac brown (6 E 7) or rusty brown (6 E 8) on white background. Lamellae: 3–8 mm wide, 8–11 lamellae present along 1 cm near the pileus margin, narrowly adnate, first white, with maturity yellow white (4 A 2) to cream (4 A 3) coloured, with frequent furcations, especially near the stipe attachment, anastomoses absent, lamellulae usually absent, only few observed in one collection, edges entire, concolourous. Stipe: 55–110 × 15–35 mm, cylindrical or slightly tapering towards the base, frequently bumpy or with 2–4 irregular depressions or constrictions corresponding to the distinct chambers inside, smooth to slightly rugose or with slight longitudinal ridges, annulus absent, white; cottony stuffed, cavernate with 3–5 distinct chambers. Context: 3–10 mm thick at half pileus radius, white, parts damaged by insects turning brownish-orange, young firm, with maturity brittle, taste burning acrid after 2–3 seconds, odour inconspicuous or sometimes slightly fruity; macrochemical reactions: guaiac after 8–10 seconds strongly positive (+++) on both stipe and lamellae surfaces, FeSO 4 strong, deeply orange, sulphovanillin negative, sometimes bluish, KOH yellow on stipe surface and context, but negative on pileus surface, phenol negative. Spore print: cream (IIb-IIc). Spores: (5.6 –) 6.2–6.6 – 7.1 (– 7.9) × (5.1 –) 5.4–5.7 – 6.1 (– 6.4) µm (n = 90), Q = (1.02 –) 1.1–1.15 – 1.21 (– 1.31), globose, subglobose to broadly ellipsoid, surface almost smooth, ornamentation very inconspicuous, composed of elements hardly visible under light microscope, ornamentation approx. 0.1 µm high as estimated by SEM, very dense weakly amyloid lines and warts forming a complete reticulum as observed by SEM, density of the individual elements not quantifiable by light microscopy; suprahilar plage small, inamyloid, covered by minute wrinkles visible only by SEM. Basidia: (31.5 –) 35.5–40 – 44.5 (– 52) × (7 –) 8–8.5 – 9 (– 10) µm (n = 61), clavate to broadly clavate, 4 - spored; basidiola approx. 5–7 µm wide, cylindrical to clavate. Hymenial cystidia: on lamellae sides (56 –) 63–77 – 91 (– 117) × (7.5 –) 9–10 – 11 (– 14) µm (n = 60), moderately numerous, 1,200 –1,400 cystidia / mm 2, predominantly clavate, sometimes subcylindrical, frequently with a slightly curved base or slightly flexuose, originating in subhymenium and somewhat protruding over basidia, thin-walled, apically obtuse, usually with a 1.5–11 µm long appendage; heteromorphous contents dense, crystalline, dispersed over the entire cell, rapidly turning to dark black in sulphovanillin. Hymenial cystidia near the lamellae edges distinctly shorter and slightly narrower, (31.5 –) 40.5–49 – 57.5 (– 76) × (6.5 –) 8–9 – 10 (– 12) µm (n = 60), cylindrical to broadly clavate, occasionally with a 1–7 µm long appendage; heteromorphous contents similar to the one in hymenial cystidia on lamellae sides. Lamellae edges: fertile, with equal representation of cystidia, basidia, basidiola and marginal cells. Marginal cells: (13.5 –) 16.5–19.5 – 23 (– 29.5) × (2.5 –) 3.5–4.5 – 5 (– 7) µm (n = 62), not well differentiated, cylindrical to subclavate, sometimes slightly bent or with a secondary septum, similar to basidiola, optically empty, thin-walled. Pileipellis: orthochromatic in Cresyl blue, sharply delimited from the underlying context, 230–300 µm deep; suprapellis a trichoderm, 50–80 µm deep, composed of erect hyphal terminations embedded in a gelatinous matrix; gradually passing to a 170–220 µm deep, strongly gelatinised subpellis of more or less parallel, moderately dense, intricate, 2.5–3.5 µm wide hyphae and abundant cystidioid hyphae. Acid resistant incrustations absent. Hyphal terminations: near the pileus margin composed of (1 –) 2–4 unbranched cells, originating in intricate hyphae of the subpellis, thin-walled or with slightly thickened walls (up to 0.5 µm), terminal cells (10.5 –) 23.5–33.5 – 43.5 (– 57) × (2.5 –) 3–3.5 – 4 (– 5) µm (n = 90), mainly attenuated, less frequently cylindrical, apically obtuse; subterminal cells mainly shorter, 3.5–7 µm wide, cylindrical or ellipsoid. Hyphal terminations near the pileus centre of (1 –) 2–5 unbranched cells, thin-walled, terminal cells of similar dimensions compared to the ones near the pileus margin (11.5 –) 17.5–28.5 – 39.5 (– 57.5) × 2.5–3.5 – 4 (– 5) µm (n = 91), cylindrical, attenuated or subulate, often more distinctly base-inflated, sometimes apically acute; subterminal cells distinctly shorter, 3–7 µm wide, ellipsoid to ovoid, forming chains before branching. Pileocystidia: near the pileus margin (23.5 –) 32–42.5 – 53 (– 86.5) × (5.5 –) 7.5–9 – 10.5 (– 14) µm (n = 60), one-celled, one two-celled cystidium observed in one collection, broadly clavate, fusiform or lanceolate, originating in the suprapellis, thin-walled, apically mainly obtuse, sometimes acute, usually occasionally with a 2.5–8 µm long appendage; heteromorphous contents dense, crystalline or banded, rapidly turning to black in sulphovanillin. Pileocystidia near the pileus centre distinctly shorter, (11.5 –) 20–32.5 – 45 (– 62) × (4.5 –) 6.5–8.5 – 10 (– 13.5) µm (n = 71), globose, ovoid, ellipsoid, fusiform, clavate or lanceolate; contents similar to the one of pileocystidia near the pileus margin. Context: with dispersed, but distinct cystidioid hyphae, approx. 6–9.5 µm wide, sparsely septate, branched, contents dispersed or sometimes almost homogenous; oleiferous hyphae absent. Etymology. Referring to the strongly acrid taste and white colour of the basidiomata. Distribution and ecology. Only known from Sudanian woodlands dominated by Isoberlinia doka in Benin. Notes. Russula acrialbida has spores with extremely low and fine ornamentation which is also present in R. roseovelata, a species with a pinkish pileipellis covered by large detaching rose-beige areolae (Fig. 7) and a pileus margin without striations (Buyck 1994). Microscopically, the latter species differs by slightly larger spores, hymenial cystidia that are up to 200 µm long and the presence of capitate terminal cells in the pileipellis with intracellular refringent transversal bands (Buyck 1994). Specimens very similar to R. acrialbida are illustrated and described in local