Protomerulius amiliavi Spirin, 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 amiliavi Spirin sp. nov.

Figs 6 G , 11 O

Holotype.

France. Aveyron: Millau, Le Causse Noir , Quercus pubescens (fallen decorticated branch), 13. XI. 2022 Spirin 16165 * ( H, isotype – PC).

Etymology.

From Amiliavum, the Roman name of Millau (the type locality).

Description.

Basidiocarps effused, smooth, waxy, greyish to greyish-ochraceous, continuous, in older parts light-brown and partly gelatinised, up to 5 cm in widest dimension, 0.1–0.2 mm thick, margin narrow, first whitish to cream-coloured, floccose, then more compact and more or less concolourous with the hymenial surface. Hyphal structure monomitic; hyphae clamped, subicular hyphae with a distinct wall to slightly thick-walled, interwoven to subparallel, 1–3 μm in diam., subhymenial hyphae thin-walled, interwoven or ascending, 1–2 μm in diam., partly glued together. Tramal cystidia abundant, hyaline or brownish, tubular-clavate, sturdy, arising from slightly thick-walled, narrow hyphae, with moderately thickened (up to 1.5 μm) walls gradually thinning-out towards the apical part, longest cystidia slightly tapering to or widened at the apex (thin-walled apical parts sometimes collapsing), (32 –) 35–103 (– 119) × (2.8 –) 3.3–5.2 (– 5.3) μm (n = 42 / 2), often in groups of 5–15. Hyphidia present, simple or sparsely branched, 1–1.5 μm in diam. at the apex. Crystals present, acicular or in stellate agglomerations, up to 15 μm in widest dimension. Basidia four-celled, longitudinally septate, ovoid-ellipsoid to subglobose, pedunculate, (7.8 –) 8.2–11.2 (– 11.8) × (6.4 –) 7.1–8.8 (– 9.0) μm (n = 40 / 2), partly glued together, stalk distinct, up to 5 × 2.5 μm, sterigmata up to 10 × 2 μm. Basidiospores ellipsoid to broadly ellipsoid, more rarely broadly cylindrical, the longest spores somewhat sigmoid, (5.9 –) 6.0–9.1 (– 9.4) × (3.5 –) 3.7–5.1 (– 5.2) μm (n = 62 / 2), L = 7.30–7.59, W = 4.25–4.39, Q’ = (1.3 –) 1.4–2.1 (– 2.3), Q = 1.67–1.80.

Distribution and ecology.

Europe ( France); decayed angiosperm wood ( Quercus ).

Remarks.

Here we introduce P. amiliavi as a close relative of P. brachysporus (Bourdot & Galzin) Spirin & Malysheva. Both species possess rather thick, normally smooth basidiocarps with a gelatinised, light-brown when mature hymenium and rather narrow, fasciculate cystidia. Protomerulius amiliavi differs from P. brachysporus in having shorter and narrower cystidia and in lacking skeletal hyphae (although they are present only in well-developed specimens of the latter species). Moreover, P. amiliavi was collected from rotten oak wood, and all verified records of P. brachysporus were collected on conifer wood.

There are two other angiosperm-dwelling European Protomerulius species that produce opaque and relatively thick, crust-like basidiocarps and thereby can be mistaken for P. amiliavi . Of them, Protomerulius dubius (Bourdot & Galzin) Spirin & Malysheva is most similar to P. amiliavi , both macroscopically, due to its partly gelatinised and brownish basidiocarps in maturity, and microscopically, having similar cystidia and nearly identical basidiospores. However, cystidia of P. dubius are perceptibly wider than in P. amiliavi , reaching 9 μm in diam., and they are usually arranged in groups of up to eight. Protomerulius pertusus Malysheva & Spirin has loose, nearly floccose basidiocarps occasionally acquiring gelatinised spots on the hymenial surface only at the very end of their development. The cystidia of P. pertusus are of nearly the same diameter as in P. amiliavi , but its basidiospores are clearly narrower (W = 3.49–4.01).

Figures

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.