Russula beenkenii Manz, F. Hampe & M. Piepenbr., 2025

Manz, Cathrin, Amalfi, Mario, Buyck, Bart, Hampe, Felix, Yorou, Nourou S., Adamčík, Slavomír & Piepenbring, Meike, 2025, Just the tip of the iceberg: uncovering a hyperdiverse clade of African Russula (Basidiomycota, Russulales, Russulaceae) species with signs of evolutionary habitat adaptations, IMA Fungus 16, pp. e 140321-e 140321 : e140321-

Russula beenkenii Manz, F. Hampe & M. Piepenbr. , sp. nov.

Figs 8 , 9 , 10

Holotype.

Benin. Borgou, N’Dali, Forêt de N’Dali , co-ord. 9°45.4'N, 2°40.1'E, alt. 360 m, Sudanian woodland, under Isoberlina doka , on sandy soil, 01. 07. 2021, leg. C. Manz, F. Hampe & G. Abohoumbo, CM-21-047 (holotype B 70 0105413 , isotype UNIPAR).

Additional material examined.

Benin. Borgou, Parakou, Forêt d’Okpara , co-ord. 9°14.8'N, 2°43.6'E, alt. 350 m, Sudanian woodland, under I. doka, Monotes kerstingii and Piliostigma thonningii (Schumach.) Milne-Redh. , on sandy soil, 16. 07. 2021, leg. C. Manz, F. Hampe & G. Abohoumbo, CM-21-132 (paratype, B 70 0105414 , UNIPAR) ; ibid. Atakora, Natitingou, Kossoucoingou , co-ord. 10°9.9'N, 1°12.1'E, alt. 500 m, Sudanian woodland, under Isoberlinia tomentosa , on rocky soil, 20. 07. 2021, leg. C. Manz, F. Hampe, G. Abohoumbo, T. C. Bogo, CM-21-152 (paratype, B 70 0105415 , UNIPAR) ; ibid. co-ord. 10°9.5'N, 1°9.5'E, alt. 330 m, Sudanian woodland, under I. tomentosa , on rocky soil, 27. 06. 2022, leg. C. Manz, S. Sarawi & A. Rühl, CM-22-232 (paratype, B 70 0105416 , UNIPAR) .

Diagnosis.

Basidiomata medium-sized, pileus surface whitish with a slightly pinkish hue, mild taste, spores with a very low ornamentation, cystidia not reacting in sulphovanillin, hyphal terminations near the pileus centre very variable and with striking patches of refractive inclusions arranged in horizontal bands, occurring in savannah woodlands. Differs from R. roseovelata by a smooth pileus cuticle without areolae.

Description.

Growth habit: basidiomata solitary or in small groups of up to five. Pileus: medium-sized, 35–75 mm in diam., when young convex, later expanding plane, slightly to distinctly centrally depressed; margin even or slightly involuted, finely striate up to 10 mm, frequently radially cracked, regular or slightly undulate; cuticle smooth, matt, peelable up to 1 / 2 – 3 / 4 of the pileus radius, colour near the centre white, yellowish-white (4 A 2), ivory (4 B 2) or with an orange white (5 A 2) hue, near the margin additionally frequently with a more or less distinct pinkish-white (10-11 A 2) hue. Lamellae: 3–6 mm wide, 8–13 lamellae present along 1 cm near the pileus margin, adnexed, sometimes even free, cream-coloured, with frequent furcations near the stipe attachment, anastomoses and lamellulae absent; edges entire, concolourous. Stipe: 30–80 × 10–20 mm, cylindrical, sometimes bent towards the base, occasionally with 2–3 constrictions corresponding to the chambers inside, smooth to slightly rugose, annulus absent, white; cottony stuffed, cavernate with 3–4 distinct chambers. Context: 1–2 mm thick at half pileus radius, white, unchanging when bruised, brittle, taste mild, odour inconspicuous, macrochemical reactions: guaiac after 8–10 seconds positive (++) on both stipe and lamellae surfaces, FeSO 4 distinctly salmon orange, sulphovanillin negative, KOH pale yellow on pileus and stipe surfaces, phenol negative. Spore print: not observed, but certainly not white, at least cream-coloured.

Spores: (5.8 –) 6.2–6.5 – 6.9 (– 7.5) × (4.8 –) 5.2–5.5 – 5.9 (– 6.4) µm (n = 120), Q = (1.07 –) 1.13–1.19 – 1.24 (– 1.35), subglobose to broadly ellipsoid, rarely ellipsoid; surface almost smooth, ornamentation very inconspicuous, composed of elements hardly visible by light microscopy, approx. 0.2 µm high as estimated by SEM, very dense weakly amyloid pustules and crests connected by numerous fine lines forming a complete reticulum, density of the individual elements not quantifiable by light microscopy; suprahilar plage small, inamyloid, partially covered by minute wrinkles only visible by SEM. Basidia: (24.5 –) 30.5–36 – 41.5 (– 49.5) × (6 –) 7.5–8.5 – 9.5 (– 10) µm (n = 60), narrowly clavate to subcylindrical, 4 - spored; basidiola approx. 4–7 µm wide, cylindrical to narrowly clavate. Hymenial cystidia: on lamellae sides (43 –) 63.5–74 – 84.5 (– 100) × (6 –) 7.5–9 – 10 (– 11.5) µm (n = 60), subcylindrical to slightly clavate or fusiform, frequently with a slightly curved base or slightly flexuose, originating in subhymenium and somewhat protruding over basidia, thin-walled, apically obtuse, rarely acute, with a 1.5–16 µm long appendage; heteromorphous contents dense, amorphous or crystalline, sometimes located only in the upper two thirds, not reacting to sulphovanillin. Hymenial cystidia near the lamellae edges distinctly shorter, (32 –) 37–42 – 47 (– 52) × (5 –) 6–7 – 8 (– 11) µm (n = 60), cylindrical to slightly clavate or fusiform, usually with one or sometimes two (2.5 –) 3.5–5.5 – 7.5 (– 12) µm long appendages; heteromorphous contents slightly less dense than in cystidia on lamellae sides. Lamellae edges: fertile with equal representation of cystidia, basidia, basidiola and marginal cells. Marginal cells: (12 –) 19–25 – 31 (– 42) × (3 –) 4–5 – 6 (– 9) µm (n = 64), fusiform, lanceolate or utriform, less frequently cylindrical or subclavate and then hard to distinguish from basidiola, optically empty, thin-walled. Pileipellis: orthochromatic in Cresyl blue, gradually passing to the underlying context, 95–110 µm deep; suprapellis a trichoderm, 25–35 µm deep, composed of erect hyphal terminations, gelatinised; gradually passing to a 65–80 µm deep subpellis of loosely interwoven, irregularly orientated, 2.5–3 µm wide hyphae, becoming denser and horizontally orientated near the context, gelatinised in the distal part, cystidioid hyphae present. Acid resistant encrustations absent. Hyphal terminations: near the pileus margin composed of 1–3 unbranched cells, thin-walled, with occasional refractive inclusions, terminal cells (10 –) 18.5–27.5 – 36.5 (– 47) × (2.5 –) 3.5–4 – 4.5 (– 6) µm (n = 92), cylindrical or slightly tapering towards the apex, apically obtuse; subterminal cells distinctly shorter, 3.5–10 µm wide. Hyphal terminations near the pileus centre very variable, composed of 1–5 unbranched cells, thin-walled, often with conspicuous refractive patches, frequently arranged in a horizontal band pattern, also frequently observed in hyphae of the subpellis, terminal cells distinctly longer and slightly narrower (8 –) 9–22 – 35 (– 77) × (2 –) 2.5–3.5 – 4 (– 6.5) µm (n = 94), cylindrical or tapering towards the apex; subterminal cells shorter, 3–8 µm wide. Pileocystidia: near the pileus margin (21 –) 23.5–29.5 – 35.5 (– 43.5) × 3.5–4.5 – 5 (– 7) µm (n = 61), one-celled, predominantly lanceolate, sometimes subcylindrical, originating in the suprapellis, thin-walled, apically obtuse, with a 1–3 µm long terminal knob; heteromorphous contents moderately dense, granulose, sometimes concentrated in the apical part, also frequent in subterminal cells, not reacting to sulphovanillin. Pileocystidia near the pileus centre similar in size, shape and contents to pileocystidia near the pileus margin (17 –) 24.5–33 – 41 (– 61.5) × (3 –) 3.5–4.5 – 5 (– 6) µm (n = 60). Context: without cystidioid hyphae, oleiferous hyphae frequent.

Etymology.

After the German mycologist Ludwig Beenken, honouring his contribution to the knowledge on the diversity of the ECM morphology within the genus Russula .

Distribution and ecology.

Known from Sudanian woodlands dominated by Isoberlinia spp. in Benin. Distributed also in Zimbabwe.

Notes.

Russula beenkenii has spores with extremely low ornamentation, as in R. roseovelata . The latter species can be distinguished by its distinctly rose coloured, areolate pileus, the absence of gelatinisation in the suprapellis, cystidia that are greying in sulphovanillin and distinctly wider pileocystidia ( Buyck 1994).

Figures

Figure 8. Russula beenkenii A – D field pictures of basidiomata: A CM- 21-047, holotype, B CM- 21-132, C CM- 21-152, D CM- 22-232; E, F scanning electron microscopical pictures of basidiospores (both CM- 21-047, holotype). Scale bars: 3 cm (A, D); 2 cm (B); 1 cm (C); 3 µm (E, F).

Figure 9. Hymenial elements of Russula beenkenii. (holotype, CM- 21-047) A basidia and basidiola, B hymenial cystidia near the lamellar edges, C marginal cells, D hymenial cystidia, E spores as seen in Melzer’s reagent. Scale bar: 10 μm, but only 5 μm for spores.

Figure 10. Elements of the pileipellis of Russula beenkenii. (holotype, CM- 21-047) A, B elements near the pileus centre: A hyphal terminations, B pileocystidia; C, D elements near the pileus margin: C hyphal terminations, D pileocystidia. Scale bar: 10 μm.