Marasmiellomycena pseudoomphaliiformis Antonín & Ševčíková, sp. nov.

Index Fungorum number: IF 900584; MycoBank number: MB 900584; Facesoffungi number: FoF 14223; Fig. 1

Etymology – species epithet refers to the close resemblance of this species to M. omphaliiformis.

Diagnosis – differs from M. omphaliiformis by distinct ITS and LSU sequences and by the geographic distribution in North America.

Macromorphology – Pileus 4–16 mm, convex with plane, slightly papillate or slightly depressed centre when young, then±applanate and omphalioid, funnel-shaped at the end, with small central umbilicus, with involute to straight, finally uplifted, slightly undulate margin, entirely finely tomentose to pubescent when young, partly glabrescent when old, but with constantly pubescent margin, hygrophanous, slightly translucently striate in older basidiomata, distinctly radially grooved at margin when old, with small brown radial fibrils, most close and suberect at centre, less frequent and adpressed at margin, dark watery brown (up to 8E7) when moist and very young then whitish to pale beige (c. 5B2‒3) with darker centre, in mature basidiomata watery beige to greyish (slightly paler than 5B2‒4), or greyish (between 6B3 and 6C3), sometimes brownish or brown (c. 7D6, 7E8) when moist, drying-up to whitish. Lamellae distant, L=14–17, l=1–2(‒3), broadly adnexed when young, almost triangular and shortly decurrent when old, intervenose and sometimes forked especially when old, white to cream-white or beige (c. 6B3), with concolorous, finely pubescent edge. Stipe 5‒11×0.6‒1.3 mm, central to slightly eccentric, subinsititious, cylindrical when very young, then tapering towards base, broadened into a small disc at base, entirely white pubescent, finely longitudinally fibrillose in lower part, basal hairs brown, slightly carneous tinged (paler than 8B2) when very young, then whitish to pale brownish at apex and dark brown to black-brown (7F6‒7, 9F5, 9F8) at base and sometimes entirely dark brown when old. Context without distinct smell and taste, very thin, in pileus whitish and greyish under pileipellis, in stipe hollow, cortex concolorous with the colour of stipe surface.

Micromorphology – Basidiospores (6.5‒)7.0–9.0(‒9.5)×4.0–5.5 μm, average 7.93×4.64 μm, E=1.55–1.88(‒2.0), Q=1.69‒1.75, ellipsoid, ellipsoid-fusiform, smooth, inamyloid, non-dextrinoid. Basidia (21.5‒)29–33×6.1–9.0 μm, 4-spored. Basidioles 15–34×3.5–8.0 μm, clavate, subfusiform or cylindrical. Cheilocystidia 25–87 × 9.0–18 μm, sometimes indistinct, (irregularly) clavate, fusiform to lageniform, sometimes with up to 40 μm long, tapering neck. Trama hyphae±cylindrical, colourless, thin-walled, up to 17 μm wide. Pileipellis a cutis composed of cylindrical, smooth or incrusted, sometimes with brown walls, 3.0‒9.2(‒14) μm wide hyphae; terminal cells in groups (especially towards margin), (7.2‒)20‒88×(3.2‒)4.8‒12. 3 µm, irregularly cylindrical to narrowly clavate or clavate, often with coloured walls; awl-shaped cells (pileocystidia) present especially towards centre. Stipitipellis a cutis of cylindrical, ± slightly thick-walled, 2.5‒8.5 μm wide hyphae. Caulocystidia (17.8‒)20–50×5.2–12 μm, fusiform, clavate, sometimes rostrate, thin- to slightly thick-walled. Trama and cystidia metachromatic in Cresyl blue. Clamps present in all studied tissues.

Hosts and geographical distribution – On decaying wood of a broad-leaved tree and leaves veins in amixed forest (Acer, Carya, Pinus, Quercus, Rhododenron, Tsuga); USA, Tennessee and North Carolina. Holotype: USA, Tennessee, Blount Co., Great Smoky Mts. Nat. Park, Parsons Branch Road, Gregory Ridge Trail, 29 July 1991 leg. V. Antonín 91/277 (BRNM 552721).

Additional material examined – USA, Tennessee, Blount Co., Great Smoky Mts. Nat. Park, Parsons Branch Road, 31 July 1991 leg. et det. V. Antonín 91/297 (BRNM 552653). USA, Tennessee, Blount Co., Great Smoky Mts. Nat. Park, Cades Cove, Crib Gap, 22 July 1991 leg. et det. V. Antonín 91/242 (BRNM 552654). USA, North Carolina, Swain Co., Great Smoky Mts. Nat. Park, Kephart Prong Trail, 25 July 1991 leg. et det. V. Antonín 91/258 (BRNM 552658).

Notes – Our collections (BRNM 552721, BRNM 552653, BRNM 552654, BRNM 552658) are morphologically identical and they are characterized by an omphalinoid habit, a small, mostly pale coloured pileus, broadly adnexed to (shortly) decurrent, white, cream-white, or beige lamellae, a short, central to slightly eccentric, subinsititious, entirely white pubescent stipe, ellipsoid, ellipsoid-fusiform Basidiospores, (irregularly) clavate, fusiform to lageniform cheilocystidia, a pileipellis a cutis with irregularly cylindrical to narrowly clavate, clavate or awl-shaped terminal cells, and fusiform, clavate, sometimes rostrate caulocystidia. Our collections formed a well-supported clade with strains of Porotheleum omphaliiforme (Fig. 2). The blastn searches with NCBI revealed most similar species to our collection as P. omphaliiforme (OM422782) with 97.1% (ITS) respective P. omphaliiforme (OM423656) with 99.5% sequence similarity (LSU). However, our collections are morphologically different from P. omphaliiforme. Consiglio et al. (2022) mentioned that Hydropus omphaliiformis (PBM4282, ITS: MT196987), collected in the USA is phylogenetically distant from Hydropus sensu stricto. representing an undescribed species. Therefore, our collections together with P. omphaliiforme represent a generic lineage and herein introduce as Marasmiellomycena. Our collections represent a distinct lineage which is sister to P. omphaliiforme and we introduce this clade as Marasmiellomycena pseudoomphaliiformis.

Figure 1 – Marasmiellomycena pseudoomphaliiformis (Drawing based on BRNM 552721). a Basidiomata. b Cheilocystidia. c Basidia. d Stipitipellis with caulocystidia. e Basidiospores. f Pileipellis with pileocystidia. Scale bar=10 μm

Figure 2 – Phylogram generated from maximum likelihood analysis based on combined ITS and LSU sequence data. Maximum likelihood bootstrap supports (≥ 60%) followed by Bayesian posterior probabilities (≥0.70) followed by supports are indicated. The dataset was compiled using data from previous studies of Clitocybula, Gerronema, Hydropus and Megacollybia (Matheny et al. 2006; Antonín et al. 2019; Kaygusuz et al. 2020; Consiglio et al. 2022) and the most similar sequences (>91% sequence similarity in LSU rDNA) were selected from GenBank using BlastN similarity search tool. The ITS and LSU sequences originating from the single voucher or strain were concatenated (93 sequence pairs). Sequence alignment generated in MAFFT 6 (Katoh and Toh 2008) was curated manually to remove hypervariable regions. Bayesian searches were conducted in MrBayes 3.0 (MB) with 10 million replicates. Maximum likelihood searches were conducted in IQ-TREE multicore version 1.4.1. in IQ-TREE including standard automated model selection (“-m TEST”) as well as FreeRate (+R) model, and standard nonparametric bootstrap approximation (“-b 1000”). The dataset had 1872 columns, 1225 distinct patterns, 735 parsimony-informative characters, 249 singleton sites, 888 constant sites. The substation models for MB (TPM2+F+I+G4 for both partitions) were estimated in jModeltest 0.1.1. Two data partitions (one for each subunit) were recognized in the rDNA concatenated dataset. For each terminal, the species name and the voucher/herbarium code are indicated, and the type strains are in bold and new isolates are in blue bold. *Gerronema genera sensu (Vizzini et al. 2019)