Protomerulius deceptorius Spirin & Viner, 2025

Spirin, Viacheslav, Malysheva, Vera, Viner, Ilya, Alvarenga, Renato Lúcio Mendes, Grebenc, Tine, Gruhn, Gérald, Savchenko, Anton, Grootmyers, Django, Ryvarden, Leif, Vlasák, Josef, Larsson, Karl-Henrik & Nilsson, R. Henrik, 2025, Additions to the taxonomy of the Auriculariales (Basidiomycota) with pedunculate basidia, MycoKeys 120, pp. 339-392 : 339-392

Protomerulius deceptorius Spirin & Viner sp. nov.

Figs 6 H , 11 P

Holotype.

Slovenia. Kočevje: Podstenice, Rajhenavski Rog , Fagus sylvatica (rotten decorticated log), 19.VIII.2021 Spirin 14811 * ( H, isotype – LJF).

Etymology.

Deceptorius (Lat., adj.) – deceptive, in reference to small morphological differences from the closely related species.

Description.

Basidiocarps effused, smooth, first pruinose-reticulate, waxy, semitranslucent, greyish, then continuous, gelatinised, up to 1 cm in widest dimension, 0.03–0.07 mm thick, margin concolourous with hymenium, gradually thinning-out; tiny white spots often present in mature basidiocarps, irregularly distributed on hymenial surface. Hyphal structure monomitic; hyphae clamped, subicular hyphae with a distinct wall, subparallel, 2–3 μm in diam., subhymenial hyphae thin-walled or with a distinct wall, interwoven or ascending, 1.5–2.5 μm in diam., glued together. Tramal cystidia abundant, hyaline or brownish, tubular-clavate, usually tapering but sometimes slightly widened at the apex, arising from thin- or moderately thick-walled hyphae, with thickened (up to 3 μm) walls gradually thinning-out towards the apical part (thin-walled apical parts often collapsing), (45 –) 46–124 (– 127) × (5.2 –) 5.3–11.3 (– 11.8) μm (n = 134 / 7), single or in groups of 2–5, occasionally biradicate, sometimes tortuous; hymenial cystidia hyaline, broadly clavate to subglobose, thin-walled, quickly collapsing, 12–26 × 5.2–12.4 μm, scattered among basidia. Hyphidia present, simple or sparsely branched, 1–1.5 μm in diam. at the apex. Crystals occasionally present on hyphidia and cystidia, acicular or fused in stellate agglomerations. Basidia four-celled, longitudinally septate, ovoid-ellipsoid, pedunculate, (6.9 –) 7.0–9.1 (– 9.8) × (6.0 –) 6.1–7.2 (– 7.8) μm (n = 21 / 2), tightly glued together, stalk distinct, up to 4 × 3 μm, sterigmata up to 5 × 1.5–2 μm. Basidiospores smooth, thin-walled, ellipsoid to broadly cylindrical or cylindrical, more rarely lacrymoid, (4.6 –) 4.8–6.8 (– 7.2) × (3.0 –) 3.1–4.7 (– 4.9) μm (n = 210 / 7), L = 5.54–5.94, W = 3.59–4.11, Q’ = (1.2 –) 1.3–1.8 (– 1.9), Q = 1.44–1.63.

Ecology and distribution. Europe ( Slovenia – basidiocarps on wood; Estonia, Georgia, Portugal, and Romania – soil sequences), North America ( USA, West Virginia – soil sequence) (see further remarks below); strongly rotten wood of deciduous trees ( Fagus , Salix ).

Remarks.

Protomerulius deceptorius is introduced here as a close relative of P. commotus and P. madidus (Figs 1 , 4 ). Morphologically, it is highly similar to P. commotus and differs from it primarily in having shorter tramal and smaller hymenial cystidia. Moreover, basidiospores of P. deceptorius are slightly wider than in P. commotus , although this difference is merely statistical, and the significant part of P. deceptorius specimens have basidiospores of the same size as in P. commotus . Mature basidiocarps of P. deceptorius usually contain white mineral inclusions (Fig. 6 ); they are absent in all P. commotus specimens studied by us.

In total, eleven specimens of P. deceptorius are known to us, all collected in Slovenia and all but one derived from rotten wood of Fagus sylvatica . However, DNA sequences obtained from forest soil and root tips indicate that the species seems to be widely distributed in Europe (Fig. 4 ). GenBank sequence MF 665126 from West Virginia, USA, shows a 1 bp difference in the ITS 2 region versus P. deceptorius from Europe. We consider it as an intraspecific variation and assign this sequence to P. deceptorius . It was obtained from root tips of trees in a montane forest dominated by Fagus grandifolia and Quercus spp. ( Nelson 2017). Several other soil sequences from GenBank and UNITE cluster with P. deceptorius , although without statistical support (Fig. 4 ). These all originated from subtropical and tropical areas (South America, Southeast Asia, and Oceania) and may well represent sister taxa of P. deceptorius . On the other hand, their differences versus P. deceptorius sequences from Europe and North America may reflect genetic variation within one widely distributed species. Some other Protomerulius species with a wide distribution range (e. g., P. brachysporus , P. minor , and P. subreflexus ) demonstrate significant ITS variation within one species ( Spirin et al. 2019 c). Whatever the case may be, a definite conclusion can be reached only after sequencing the full-length ITS region and, desirably, additional genetic markers from physical P. deceptorius s. lato specimens collected in subtropical and tropical areas.

Figures

Figure 1. Bayesian majority-rule consensus ITS + LSU-based tree of the Auriculariales overlaid with bootstrap support values from the maximum likelihood analysis. Support values are given as Bayesian posterior probabilities / ML bootstrap percentages. Species with stalked basidia are marked with a red X. I – Protohydnum clade; II – Elmerina clade; III – Hydrophana clade; IV – Endoperplexa – Mycostilla clade; V – Protoacia – Gelacantha clade; VI – Protomerulius clade; VII – Myxarium clade. The Sebacinales (Ditangium P. Karst., Sebacina, and Serendipita P. Roberts spp.) and Exidiopsis gloeophora were used as outgroups.

Figure 4. Bayesian majority-rule consensus ITS-based tree of the Protomerulius clade. Support values are given as Bayesian posterior probabilities. Psilochaete multifora Spirin & Malysheva was used as an outgroup.

Figure 6. Basidiocarps of: A. Hydrophana trichiesiana (holotype); B. Mycostilla chromatica (holotype); C. Myxarium guianense (holotype); D. Protoacia reliqua (holotype); E. Protohydnum erumpens (holotype); F. P. livescens (specimen Spirin 15619); G. Protomerulius amiliavi (holotype); H. P. deceptorius (specimen Spirin 16784). Scale bar: 1 cm.

Figure 11. Basidiospores of: A. Protohydnum album (specimen Miettinen 196583); B. P. aureum (holotype); C. P. elasticum (holotype); D. P. elevatum (holotype); E. P. erumpens (holotype); F. P. galzinii (three left – specimen Miettinen 15900.4, three right – lectotype of S. galzinii); G. P. lactescens (four left – specimen TAAM 192048, three right – holotype of S. lactescens); H. P. livescens (specimen Spirin 13913); I. P. microperum (holotype); J. P. nudum (holotype); K. P. ocellatum (holotype); L. P. pallidum (holotype); M. P. pululahuanum (three left – lectotype, three right – specimen FH 00783538); N. P. sucinum (three left – lectotype of A. brasiliensis, three right – specimen BPI 701268); O. Protomerulius amiliavi (holotype); P. P. deceptorius (holotype). Scale bar: 10 µm.