Russula mollicula

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 mollicula nom. prov.

Figs 29 , 30 , 31

Material examined.

Benin. Donga, Bassila , co-ord. 9°0.1'N, 1°38.9'E, alt. 360 m, in a gallery forest, under Berlinia grandiflora , on sandy soil, 30. 06. 2022, leg. C. Manz, F. Hampe, S. Sarawi, A. Rühl & R. Dramani, CM-22-244 ( B 70 0105434 , UNIPAR) .

Short description.

Basidiomata small and ephemerous, pileus surface whitish to pale pinkish, pileocystidia distinctly inflated, broadly fusoid with dense crystalline contents and pileipellis a trichoderm composed of long, narrowly lanceolate terminal cells on top of short and inflated subterminal cells, occurring in gallery forests.

Growth habit: basidiomata solitary. Pileus: small, 20 mm in diam., plane, centrally deeply depressed; margin uplifted, strongly tuberculate-striate up to ½ of the pileus radius, somewhat undulate and slightly crenulate; cuticle smooth, matt, not peelable, colour near the margin white, near the centre pinkish-white (10 A 2). Lamellae: approx. 2 mm wide, 8–9 lamellae present along 1 cm near the pileus margin, narrowly adnate, white, furcations, anastomoses and lamellulae absent; edges entire, concolourous. Stipe: 27 × 4 mm, cylindrical, bulging here and there, smooth, annulus absent, white; hollow. Context: approx. 0.5 mm thick at half pileus radius, white, unchanging when bruised, brittle, taste mild, odour inconspicuous, macrochemical reactions not observed. Spore print: not observed, probably white or cream.

Spores: (9.4 –) 9.9–10.3 – 10.8 (– 11.3) × (9.1 –) 9.4–9.8 – 10.3 (– 10.7) µm (n = 30), Q = (1 –) 1.02–1.05 – 1.08 (– 1.11), globose to subglobose, ornamentation of distant amyloid spines (1–3 in a circle of 3 µm diam.), 1.8–2.6 µm high, abundantly connected by distinct lines [1–3 (– 5) in the circle] forming a complete reticulum, isolated elements absent, spines and line connections with frequent secondary warts only visible by SEM, suprahilar plage medium-sized, with a distinct central amyloid spot. Basidia: (32.5 –) 36–41.5 – 46.5 (– 49.5) × (12 –) 13–14 – 15 (– 16) µm (n = 20), broadly clavate, 4 - spored; basidiola approx. 9–12 µm wide, clavate. Hymenial cystidia: on lamellae sides (83 –) 91.5–99.5 – 107.5 (– 109.5) × (13 –) 15–17 – 18.5 (– 21.5) µm (n = 20), widely dispersed, 100–135 / mm 2, fusiform, originating in subhymenium and somewhat protruding over basidia, thin-walled, apically obtuse, with a 4–10 (– 15) µm long appendage; heteromorphous contents predominantly densely crystalline, turning dark grey violet in sulphovanillin. Hymenial cystidia near the lamellae edges distinctly shorter and narrower, (47.5 –) 51–63 – 75 (– 88) × (10 –) 11–12.5 – 14.5 (– 15.5) µm (n = 20), shape and heteromorphous contents similar to the one on hymenial cystidia on lamellae sides. Lamellae edges sterile, densely covered with marginal cells. Marginal cells: (19 –) 20–32.5 – 45 (– 67) × (6 –) 7.5–8.5 – 9.5 (– 11) µm (n = 20), fusiform or lanceolate, sometimes with long appendages, optically empty, thin-walled. Pileipellis: orthochromatic in Cresyl blue, sharply delimited from the underlying context, 80–105 µm deep; suprapellis a trichoderm, 23–38 µm deep, composed of a thin layer of erect, not gelatinised hyphal terminations arranged in tufts; well delimited from the 55–73 µm deep subpellis, of loose, gelatinised, interwoven, irregularly orientated, 3–5 µm wide hyphae, becoming denser and horizontally arranged towards the context. Acid resistant encrustations absent. Hyphal terminations: near the pileus margin composed of (1 –) 2 unbranched cells, thin-walled, terminal cells (18.5 –) 27.5–37 – 46.5 (– 63.5) × (2.5 –) 3–3.5 – 4 (– 5) µm (n = 30), attenuated, subulate, slender, slightly flexuous, apically obtuse; subterminal cells distinctly shorter, 3.5–6.5 µm wide, cylindrical, ellipsoid or subglobose. Hyphal terminations near the pileus centre composed of up to 3 unbranched cells, terminal cells (15 –) 26.5–36 – 45.5 (– 56.5) × (2.5 –) 3–3.5 – 4.5 (– 5.5) µm (n = 30), similar in shape to the ones near the pileus margin; subterminal cells shorter, 3.5–10 µm wide, inflated, ellipsoid to subglobose. Pileocystidia: near the pileus margin (28 –) 30–39.5 – 49 (– 66) × (11 –) 12.5–14.5 – 16.5 (– 18) µm (n = 20), one-celled, inflated, broadly fusiform, originating in the suprapellis, thin-walled, apically obtuse, with a 3–16 µm long finger-like appendage; heteromorphous contents dense, crystalline, turning to grey, surrounding cytoplasm to dark pink in sulphovanillin. Pileocystidia near the pileus centre similar in size and shape to those near the pileus margin (25 –) 27.5–39 – 50 (– 66) × (11 –) 12–14 – 16.5 (– 19.5) µm (n = 20), with a single or rarely two, 3–18 µm long appendages; heteromorphous contents similar. Context: without cystidioid and oleiferous hyphae.

Etymology.

molliculus (lat.) = dainty, tender. Referring to the small and tender habit of the basidiomata of this species.

Distribution and ecology.

Only known from the Bassila gallery forest in Benin.

Notes.

So far, R. mollicula nom. prov. is the only “ Afrovirescentinae ” species with a consistently and distinctly amyloid spot on the suprahilar plage. Despite this striking diagnostic character and well-defined position in our phylogeny (Fig. 1 ), we refrain from formally describing it as a new species because we only studied a single collection. As the specimen was collected under very moist weather conditions, we were not certain if the species has a partial veil and we were unable to document the macrochemical reactions and the variability of the pileus colours. Russula roseoalba is very similar in field aspect, but differs by more slender pileocystidia with less crystalline contents and hyphal terminations in the pileipellis composed of longer chains of cells.

Figures

Figure 1. Phylogenetic Maximum Likelihood tree of Russula subg. Heterophyllidiae, based on concatenated LSU, mtSSU, tef 1, rpb 1 and rpb 2 sequence data with bootstrap (ML) and Bayesian Inference (BI) values indicated over the branches. Branches in bold are supported by ML ≥ 75 or BI ≥ 0.95; black – with full support by both analyses (ML = 100, BI = 1.00), blue – supported by both ML and BI, grey – supported only by one analysis, asterisk (*) indicates full support. Highlighted species are described and illustrated in this study. Labels of holotypes of newly-described species are written in bold. Habitats (gallery forests or savannah woodlands), sizes of basidiomata (small and thin-fleshed or large and thick-fleshed) and prominence of spore ornamentation (low and high) for species occurring in Benin are indicated by icons.

Figure 29. Russula mollicula nom. prov. (CM- 22-244) A field picture, B scanning electron microscopical picture of basidiospore with a prominent spot on the suprahilar plage. Scale bar: 1 cm (A); 3 µm (B).

Figure 30. Hymenial elements of Russula mollicula nom. prov. (CM- 22-244) 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 31. Elements of the pileipellis of Russula mollicula nom. prov. (CM- 22-244) 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.