Marasmiellomycena omphaliiformis (Kühner) Mateos, Kolařík, De la Peña-Lastra, Ševčíková & Antonín, comb. nov.
Index Fungorum number: IF 900585; MycoBank number: MB 900585; Facesoffungi number: FoF 14224; Figs. 1, 2
Basionym – Marasmius omphaliiformis Kühner, in Kühner & Romagnesi, Bull. Soc. nat. Oyonnax 8: 75, 1954
Synonym – Porotheleum omphaliiforme (Kühner) Vizzini, Consiglio & M. Marchetti, Rivista di Micologia 64: 110. (2021) 2022;
Marasmiellus omphaliiformis (Kühner) Noordel., [as ‘omphaliformis’], Persoonia 12 (1): 35. 1983;
Hydropus omphaliiformis (Kühner) Honrubia, [as ‘omphaliformis’], Cryptog. Mycol. 5 (1): 57. 1984;
Mycena lapalmaensis Dähncke & Robich, Bol. Soc. Micol. Madrid 34: 99. 2010
Holotype – France, Charente Maritime, Corniche de Nauzan pres Royan, 2 September 1935, R. Kühner (fragm. in PC).
Macromorphology – Pileus 1–5 mm, hemispherical, convex, plano-convex and/or with umbilicate, sometimes somewhat depressed centre when mature, with involute, not translucently striate, not hygrophanous, not radially grooved margin, Pileipellis distinctly pruinose, whitish pubescent, with innate conglomerated fibrils and also granulate appearance; cream-coloured in the background and reddish-brown fibres when young (Ség. 250), turning greyish or sordid with age (Ség. 694), especially in the center. Lamellae distant, L=14–16, l=0–1, arcuate-decurrent, sometimes forked, and somewhat intervened in the background, larger, creamwhite to pale ochre with a slightly darker edge, with whitish abundant hairs on the lamellar edge. Stipe 5–10×0.6–1 mm, cylindrical, sometimes broadened towards the base, sometimes bulbous, pale ochre at the top, ochre in the middle part (Ség. 250) and turning dark brown (Ség. 701) to blackish in the lower part (Ség. 706), pubescent, formed by whitish hairs distributed along its entire length, non-insititious, with basal hairs. Species thin-fleshed, often with elastic, cartilaginous or leathery flesh and which generally dry out without rotting, reviviscent appearance.
Micromorphology – Spores (6.3–)7.5–8.6–9.9(–10.3) × (3.7–)3.8–4.1–4.6(–4.9) µm; Q=(1.5–)1.8–2.1–2.3(–2.6); n=32; Vm =78 µm3 , smooth, narrowly ellipsoid or subcylindrical, ellipsoid, sublacrymoid or sometimes fusiform, with thick apiculum, usually with one, two or more oily guttules. Basidia 20–37 × 4–7 µm, claviform, with sterigmata 3–3.5 µm high, tetrasporic. Basidioles claviform or subcylindrical, 18–35×4–6.5 µm. Lamellar edge low fertile and heterogeneous, cheilocystidia numerous, 37–58 × 5.7–7.6 µm, sublageniform, with slightly broadened base and flagelliform neck (1.7–3.5 µm). Pleurocystidia absent. Hymenophoral trama subregular, 2.5–6.0 µm wide hyphae, trama elements 99–120×15–31 µm, abundant, fusiform, sometimes thick-walled. Pileipellis an irregular cutis with transitions to a trichoderm, made up of
3–10 µm wide cylindrical hyphae, with scattered suberect or erect fusiform, sublageniform or flagelliform, thin-walled, weakly diverticulate terminal elements, very polymorphous, 30–56×6–10.3 µm; with brown intracellular pigment. Stipitipellis a cutis of parallel, cylindrical, smooth, 2–6.0 µm wide hyphae, with dark brown intracellular pigment. Caulocystidia numerous along the entire length of the stipe, (15.1–)30.8–62.6(–65.8)×(2–)2.4–11, 6(–15.5) µm, fusiform, subclavate, sublageniform, sometimes with digital projections, usually narrowed at the apex or large rostrum. Clamps present in all tissues. Chemical reactions no part of the basidiocarp dextrinoid or amyloid, except the spores which are slightly amyloid. Cresyl blue negative in all tissues. KOH 10% slightly yellowish in the subpellis.
Material examined – Spain, Galicia, Pontevedra, Vilagarcía de Arousa, Parque Nacional das Illas Atlánticas de Galiia, Illa de Cortegada, N42o 37′ 1.29″ W8o 47′ 10.97″, 10 m a.s.l., growing on the lower part of a living trunk of Quercus robur L., 22 August 2020, S. De la Peña-Lastra, AMI-SPL252.
GenBank numbers– ITS: MZ542542, LSU: MZ542546.
Hosts and geographical distribution – Saprobic on a woody trunk of Quercus robur; northwestern Spain.
Notes – Our collection (AMI-SPL252) and another unpublished collection (AMI-SPL250) were consistently showed negative Cresyl blue reaction in all tissues, in many preparations at various temperatures (up to 70 °C). Noordeloos (1983) mentioned the metachromatic reaction of the trama in Cresyl blue as one of the crucial features of this species together with its trichodermal pileipellis and almost setiform/flagelliform elements. Consiglio et al. (2022) also emphasized this feature as stable within this very variable species. Also caulocystidia with digital projections are atypical for Marasmiellomycena omphaliiformis. However, collection AMI-SPL252 clustered and is identical to M. omphaliiformis. Thus, its variability is larger than these authors expected. Marasmiellomycena omphaliiformis is a morphologically variable species (Antonín and Noordeloos 1993, 2010; Consiglio et al. 2022) (Figs. 1, 2).
Figure 1 – Marasmiellomycena omphaliiformis (AMI-SPL252). a Habitat. b Basidiomata (RC,MLZ). c Basidiospores (RC, MLZ). d Cheilocystidia (RC). e Hymenophoral trama elements (RC). f Chemical reactions: 1–2, trama of lamellae (MLZ, KOH); 3–4, trama subpellis (MLZ, KOH); 5–6, trama stipitipellis (MLZ, KOH); 7 trama subpellis (BC); 8, trama stipitipellis (BC). g Hymenium (RC). h Pileipellis (RC). i Caulocystidia and stipitipellis. Scale bars: c–i=10 μm
Figure 2 – Line drawing of Marasmiellomycena omphaliiformis (AMI-SPL252). a Basidiomata. b Cheilocystidia. c Basidiospores. d Hymenophore with basidia, basidioles and trama elements. e Stipitipellis and caulocystidia. f Pileipellis. Scale bars: b–f=10 μm