Hydrophana fessula Viner & 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

Hydrophana fessula Viner & Spirin sp. nov.

Fig. 8 B

Holotype.

Finland. Uusimaa: Helsinki, Talosaari , Picea abies (fallen decorticated log), 13.X.2021 Viner 2021 / 289 * ( H 6112924 ).

Etymology.

Fessulus (Lat., adj.) – limp; in reference to quickly collapsing hyphae.

Description.

Basidiocarps effused, up to 4 cm in widest dimension, smooth or tuberculate, gelatinous, semitranslucent, greyish, 0.4–0.7 mm thick, in dry condition vernicose, hardly visible, margin gradually thinning-out. Hyphal structure monomitic, hyphae hyaline, clamped; subicular hyphae with a distinct wall, interwoven, 2–4 μm in diam., subhymenial hyphae thin-walled, quickly collapsing, ascending or interwoven, 2–3 μm in diam. Cystidia absent. Hyphidia abundant, richly branched, 0.5–1 μm in diam. at the apex, partly covering hymenial cells. Basidia four-celled, longitudinally septate, broadly ellipsoid to globose, pedunculate, (8.7 –) 8.8–10.2 (– 10.8) × (7.2 –) 7.3–8.7 (– 9.0) μm (n = 20 / 1), stalk distinct, up to 30 × 1.5–2.5 μm, sterigmata gradually tapering, occasionally bifurcate, up to 25 × 1.8–2.2 μm. Basidiospores smooth, thin-walled, broadly cylindrical to broadly ellipsoid, more rarely lacrymoid or ovoid, (5.2 –) 5.3–7.2 × (3.8 –) 4.0–5.2 (– 5.4) μm (n = 30 / 1), L = 6.31, W = 4.58, Q’ = (1.2 –) 1.3–1.6 (– 1.7), Q = 1.39, often with a large central oil drop.

Distribution and ecology.

Europe ( Finland); decorticated coniferous logs ( Picea ).

Remarks.

Hydrophana fessula is described here as the second European representative of the genus. It differs from H. sphaerospora mainly in having broadly cylindrical / ellipsoid basidiospores (broadly ellipsoid to nearly globose in the latter species). Moreover, H. fessula was found on coniferous wood, while H. sphaerospora seems to be restricted to deciduous trees. Ofella glaira , also inhabiting coniferous hosts, can easily be mistaken for H. fessula . However, it has thinner basidiocarps as well as wider hyphidia and sterigmata, and it occasionally produces hymenial cystidia. Basidiospores of O. glaira are more regular in shape than in H. fessula , varying from ellipsoid to subglobose (see description in Spirin et al. 2019 b). Both species seem to be very rare. While H. fessula is currently known from the type locality only, O. glaira has been detected a few times in Estonia, Finland, Norway, and Sweden (the locus classicus). Additionally, the GenBank sequence HQ 441914 of an uncultured fungus isolate from Finland ( Rajala et al. 2011) belongs to O. glaira .

Figures

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.