Russula sublaevis (Buyck) Buyck, Karstenia 33: 34 (1993)

Figs 35, 36, 37

Holotype.

DRC. Haut-Katanga, Lubumbashi; 14 km from l’Bashi, at the roadside in open forest, 02. 02. 1986, leg.: J. Schreurs, Schreurs 985 (BR 5020005285474).

Basionym.

Russula roseoviolacea f. sublaevis Buyck, Bull. Jard. Bot. Natl. Belg. 60: 204 (1990).

Additional material examined.

Benin. Atakora, Natitingou, Kota Waterfalls, co-ord. 10°12.8'N, 1°26.8'E, alt. 500 m, Sudanian woodland, under Isoberlinia tomentosa, on rocky soil, 19. 07. 2021, leg. C. Manz, F. Hampe, N. S. Yorou, G. Abohoumbo & D. Dongnima, CM-21-148 (B 70 0105437, UNIPAR); ibid. co-ord. 10°12.7'N, 1°26.6'E, alt. 500 m, Sudanian woodland, under I. tomentosa, on rocky soil, 26. 06. 2022, leg. C. Manz, F. Hampe, S. Sarawi, A. Rühl & D. Dongnima, CM-22-219 (B 70 0105438, UNIPAR); ibid. 05. 07. 2022, leg. C. Manz & F. Hampe, CM-22-281 (B 70 0105439, UNIPAR); ibid. co-ord. 10°12.4'N, 1°26.9'E, alt. 470 m, in a gallery forest, under Berlinia grandiflora & Isoberlinia doka, on the ground, 08. 06. 2002, leg. A. De Kesel, ADK 3317 (BR 5020152205127).

Short description.

Russula sublaevis is a species with medium-sized basidiomata, a bright yellow pileus, white stipe, mild taste and cream-coloured spore print. Microscopically, the small subglobose spores with a very low ornamentation are noticeable.

Description based on material recently collected Benin.

Growth habit: solitary or in groups of two. Pileus: medium-sized, 50–70 mm in diam., slightly convex to plane, centrally with a low shallow depression; margin even, finely striate up to 15 mm, regularly shaped; cuticle smooth, pruinose all over, under a magnifying glass with fine, whitish areolae, peelable up to ¾ of the pileus radius, colour yellow to bright yellow (3 A 2), becoming paler with age, near the centre sometimes slightly paler or darker. Lamellae: 5–6 mm wide, 8–9 lamellae present along 1 cm near the pileus margin, adnexed, at first white, then becoming pale cream, furcations and anastomoses absent, sometimes with dispersed lamellulae; edges entire, concolourous. Stipe: 35–45 × 8–10 mm, cylindrical, somewhat bulging here and there, smooth to slightly rugose, annulus absent, white; cottony stuffed, cavernate, with 2–3 distinct chambers. Context: 4–5 mm thick at half pileus radius, white, unchanging when bruised, brittle, taste mild, odour inconspicuous. Macrochemical reactions: guaiac after 8–10 seconds weakly positive (+) or negative (-) on stipe and positive (++) on lamellae surfaces; FeSO 4 salmon orange, sulphovanillin negative; KOH negative; phenol negative. Spore print: cream (IIc).

Spores: (5.4 –) 6–6.3 – 6.7 (– 7.1) × (4.5 –) 5.1–5.4 – 5.6 (– 6) µm (n = 90), Q = (1.06 –) 1.12–1.18 – 1.24 (– 1.31), subglobose to broadly ellipsoid; surface almost smooth, ornamentation very inconspicuous, composed of very dense, weakly amyloid pustules and crests hardly visible under light microscope, ornamentation approx. 0.1 µm high as estimated by SEM, abundantly connected by fine lines forming a complete reticulum; few scattered isolated warts only visible by SEM; suprahilar plage small, inamyloid, partially covered by even lower ornamentation only visible by SEM. Basidia: (28.5 –) 33.5–37 – 40.5 (– 46.5) × (7.5 –) 8–8.5 – 9 (– 10.5) µm (n = 60), subcylindrical to narrowly clavate, 4 - spored; basidiola approx. 4–6.5 µm wide, cylindrical to narrowly clavate. Hymenial cystidia: on lamellae sides (54.5 –) 60.5–69.5 – 78 (– 88.5) × (8 –) 9–11 – 13 (– 17) µm (n = 60), narrowly to distinctly clavate, rarely fusiform, sometimes slightly curved or bent at the base, originating in subhymenium and somewhat protruding over basidia, thin-walled, apically obtuse, sometimes with a 2.5–12 µm long appendage; heteromorphous contents amorphous, mostly located in the upper half, not reacting to sulphovanillin. Hymenial cystidia near the lamellae edges shorter and narrower, (39 –) 45.5–51.5 – 58 (– 67) × (7 –) 8.5–9.5 – 10.5 (– 12.5) µm (n = 60), narrowly to distinctly clavate, with a 2.5–13 µm long appendage, missing in some specimens; heteromorphous contents sparse, located in the apical part. Lamellae edges: fertile, with equal representation of cystidia, basidia, basidiola and marginal cells. Marginal cells: (15.5 –) 21.5–28 – 35 (– 42) × (3 –) 4–5 – 5.5 (– 7) µm (n = 60), predominantly fusiform, sometimes cylindrical or clavate, optically empty, thin-walled. Pileipellis: orthochromatic in Cresyl blue, sharply delimited from the underlying context, 200–300 µm deep; suprapellis a trichoderm, 40–50 µm deep, composed of erect, somewhat gelatinised hyphal terminations; gradually passing to a 160–250 µm deep, strongly gelatinised subpellis of loose, intricate, irregularly orientated, 2–3 µm wide hyphae, becoming gradually denser and horizontally arranged near the context. Acid resistant encrustations absent. Hyphal terminations: near the pileus margin composed of 2–4 unbranched cells, thin-walled, terminal cells (6 –) 20–32 – 44 (– 78.5) × (2.5 –) 3–4 – 5 (– 7) µm (n = 94), mainly subulate rarely cylindrical, apically obtuse; subterminal cells shorter, 3.5–4.5 µm wide, cylindrical. Hyphal terminations near the pileus centre similar to the ones near the pileus margin, terminal cells slightly narrower, (10.5 –) 16.5–29.5 – 43 (– 71) × (1.5 –) 2.5–3.5 – 4.5 (– 6) µm (n = 91); subterminal cells shorter, 2–5.5 µm wide, cylindrical. Pileocystidia: near the pileus margin (42 –) 48.5–59 – 69 (– 84.5) × (3.5 –) 4.5–5.5 – 6.5 (– 7.5) µm (n = 60), one-celled, predominantly lanceolate, sometimes subcylindrical, originating in the suprapellis, thin-walled, apically obtuse, with a 2–12 µm long appendage; heteromorphous contents amorphous, sometimes located only in the apical part, not reacting to sulphovanillin. Pileocystidia near the pileus centre slightly shorter, (34 –) 42–52 – 62 (– 75) × (3.5 –) 4.5–5.5 – 6.5 (– 8.5) µm (n = 60), similar in shape and heteromorphous contents to pileocystidia near the pileus margin. Context: without cystidioid hyphae, oleiferous hyphae frequent.

Distribution and ecology.

Widely distributed in Sudanian woodlands in tropical Africa. Kown from Benin, DRC and Zimbabwe.

Notes.

Here we provide the first detailed description of R. sublaevis, based on our recent collections from Benin which represent the first record of this species for the country. The identity of this material is confirmed by ITS sequences that are very similar to those of the holotype (Fig. 2). Morphologically, the Beninese collections differ from the holotype description by spores that are, on average, 1 µm shorter (Buyck 1994). Originally, R. sublaevis was described as a colour form of R. roseoviolacea with lower spore ornamentation, emphasising the similarity of pileipellis elements (Buyck 1990; Buyck 1994). Härkönen et al. (1993) formally combined the taxon to species rank on the occasion of a recent find from Tanzania. Buyck and Sharp (2007) reported the species from Zimbabwe from mixed miombo woodlands with Julbernardia globiflora (Benth.) Troupin and Brachystegia spiciformis Benth., Monotes A. DC. The occurrence of R. sublaevis in Zimbabwe is also confirmed by a sequenced specimen (UDB 07672946) collected in the Matobo National Park by Cathy Sharp. Further records of R. sublaevis from Tanzania, Togo and Malawi (https://www.gbif.org/ accessed on 30. 06. 2024, Härkönen et al. (1993)) remain unverified due to a lack of confirmation by corresponding sequence data and / or sufficient morphological descriptions. The species is widely distributed in sub-Saharan Africa in savannah habitats from western to eastern parts of the continent, in association with various host trees from the Fabaceae family.