Protoacia reliqua Grootmyers & 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

Protoacia reliqua Grootmyers & Spirin sp. nov.

Figs 6 D , 8 H

Holotype.

USA. Tennessee: Anderson Co., Norris, Norris Dam State Park , Juniperus virginiana (fallen decorticated log), 20.VII.2021 Grootmyers 21072014 * ( H).

Etymology.

Reliquus (Lat., adj.) – remaining, another one.

Description.

Basidiocarps effused, covering a few cm, semitranslucent, gelatinous, whitish, adnate; hymenophore hydnoid, spines acute, single, 0.05–0.1 mm long, 6–8 per mm; subiculum hardly visible, semitranslucent, 0.02–0.05 mm thick; margin gradually thinning-out. Hyphal structure monomitic, hyphae hyaline, clamped, frequently anastomosing; subicular hyphae thin-walled or with a distinct wall, interwoven, 2.5–4 μm in diam., subhymenial hyphae very thin-walled, quickly collapsing, interwoven, 2–3 μm in diam. Cystidia absent. Hyphidia abundant, richly branched, 1–1.5 μm in diam. at the apex, scattered among basidia. Basidia four-celled, longitudinally septate, broadly ellipsoid to globose, pedunculate, (7.2 –) 7.6–9.6 (– 10.2) × (5.6 –) 6.0–7.3 (– 7.5) μm (n = 20 / 1), stalk distinct, up to 25 × 2–2.5 μm, sterigmata gradually tapering, up to 22 × 2–2.5 μm. Basidiospores smooth, thin-walled, narrowly ellipsoid or ovoid to broadly cylindrical, (5.1 –) 5.2–7.7 (– 8.1) × (3.2 –) 3.3–4.5 (– 4.8) μm (n = 31 / 1), L = 6.20, W = 3.89, Q’ = (1.2 –) 1.3–1.8 (– 1.9), Q = 1.60, with a large central oil drop.

Distribution and ecology.

North America ( USA – Tennessee); rotten coniferous logs ( Juniperus spp. ).

Remarks.

Protoacia reliqua is a North American relative of P. crispans . It differs from the latter species in having shorter spines, as well as smaller basidia and basidiospores. The basidiospores of P. reliqua are not as variable in shape as those of P. crispans , varying from ellipsoid-ovoid to broadly cylindrical. The species is so far known only from the type locality but is likely overlooked due to its diminutive basidiocarps.

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 8. Basidiospores of: A. Elmericium alabastrinum (holotype); B. Hydrophana fessula (holotype); C. H. trichiesiana (holotype); D. Mycostilla chromatica (holotype); E. M. guianense (holotype); F. M. inconspicuum (holotype); G. Protoacia crispans (holotype); H. P. reliqua (holotype). Scale bar: 10 µm.