Protomerulius commotus Spirin & V. Malysheva

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 commotus Spirin & V. Malysheva , Mycological Progress 18: 1087, 2019.

Holotype.

Norway. Vestfold: Larvik, Kvelde, Jordstøyp , Ulmus glabra (rotten log), 15.IX.2016 Spirin 11097 * ( O, studied).

Description.

Basidiocarps effused, smooth, first pruinose-reticulate, waxy, semitranslucent, greyish, then continuous, gelatinised, greyish or brownish when old or dry, up to 2 cm in widest dimension, 0.05–0.1 mm thick, margin concolourous with hymenium, gradually thinning-out. Hyphal structure monomitic; hyphae clamped, subicular hyphae with a distinct wall, subparallel and densely packed, 1–2.5 μm in diam., subhymenial hyphae thin-walled, interwoven or ascending, 1.5–3 μm in diam., often short-celled, glued together. Tramal cystidia abundant, hyaline or brownish, tubular-clavate, sturdy, arising from thin-walled hyphae, with thickened (up to 3.5 μm) walls gradually thinning-out towards the apical part, the longest cystidia slightly tapering to or widened at the apex (thin-walled apical parts often collapsing), (54 –) 57–149 (– 154) × (4.2 –) 4.6–9.4 (– 11.3) μm (n = 101 / 5), single or more often in groups of 2–8, sometimes biradicate, some cystidia tortuous; hymenial cystidia hyaline, broadly clavate to subglobose, thin- or slightly thick-walled, 10–50 × 4–13.5 μm, scattered among basidia, more rarely associated with tramal cystidia. 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 to subglobose, pedunculate, (6.8 –) 7.1–9.1 (– 9.4) × (5.9 –) 6.2–7.8 (– 8.2) μm (n = 30 / 3), spaced or partly glued together, stalk distinct, up to 6 × 2.5 μm, sterigmata up to 8 × 2–2.5 μm. Basidiospores smooth, thin-walled, ellipsoid to broadly cylindrical, more rarely lacrymoid, (4.1 –) 4.4–6.8 (– 7.1) × (3.0 –) 3.2–4.3 (– 4.4) μm (n = 180 / 6), L = 5.24–5.95, W = 3.45–3.85, Q’ = (1.2 –) 1.3–1.7 (– 1.9), Q = 1.47–1.61.

Distribution and ecology.

Europe ( France, Italy, Norway, Sweden, and Switzerland – basidiocarps on wood; Czech Republic, Estonia, Germany, and United Kingdom – soil sequences); strongly decayed wood of deciduous trees ( Carpinus , Fraxinus , Quercus , and Ulmus ).

Remarks.

Protomerulius commotus was described based on two collections from Norway as a close relative of the widely distributed Protomerulius madidus Spirin & K. H. Larss. ( Spirin et al. 2019 c). Here we reassess it after investigating newly collected material and detecting one more closely related species, P. deceptorius (described below). Macroscopically, P. commotus differs from the two aforementioned species due to the lack of white mineral inclusions usually detectable without a lens; however, they are present only in mature basidiocarps of those species. Both Protomerulius commotus and P. deceptorius have broadly clavate or bubble-like hymenial cystidia, in addition to tubular thick-walled cystidia of tramal origin. Protomerulius madidus is devoid of hymenial cystidia, and its basidiospores are on average larger than in P. commotus and P. deceptorius (see description in Spirin et al. 2019 c). Differences of P. commotus from P. deceptorius are given under the latter species. Protomerulius commotus seems to be widely distributed in temperate forests of Europe (Fig. 4 ), but it is most likely overlooked due to its diminutive basidiocarps.

Figures

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.