Protohydnum nudum Spirin & Ryvarden, 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

Protohydnum nudum Spirin & Ryvarden sp. nov.

Fig. 11 J

Holotype.

Kenya. Western Province: Kakamega Forest , decayed wood, 25–27.I.1973 Ryvarden 9435 * ( O, isotype – H).

Etymology.

Nudus (Lat., adj.) – nude; in reference to exposed basidia.

Description.

Basidiocarps effused, up to 4 cm in widest dimension, smooth, gelatinous, semitranslucent, bluish-greyish to brownish, 0.1–0.2 mm thick, in dry condition light grey and rather sturdy, opaque, margin gradually thinning-out. Hyphal structure monomitic, hyphae hyaline, clamped; subicular hyphae thin-walled or with variably thickened gelatinised walls, subparallel or interwoven, glued together, 2.5–4 μm in diam., subhymenial hyphae thin-walled, predominantly ascending, often glued, 2–4 μm in diam. Gloeocystidia abundant, hyaline to yellowish, deeply rooted or arising from subhymenial hyphae, slightly tapering to the apex, often sinuous, normally embedded, 30–154 × 3.5–6.5 μm. Hyphidia abundant, richly branched, 0.5–1 μm in diam. at the apex, normally scattered among basidia, in senescent hymenium sometimes forming a continuous layer up to 10 μm thick. Basidia four-celled, longitudinally septate, ovoid-ellipsoid, pedunculate, (17 –) 17.5–23 (– 24) × (10.2 –) 10.3–12.4 (– 12.8) μm (n = 20 / 2), often exposed, stalk up to 20 × 3.5–6 (– 8) μm, sterigmata tubular, gradually tapering, up to 18 × 2–3.5 μm. Basidiospores smooth, thin-walled, ellipsoid-ovoid to broadly ellipsoid or more rarely subglobose, (7.2 –) 7.3–10.2 (– 10.6) × (5.7 –) 6.2–8.9 (– 9.0) μm (n = 60 / 2), L = 8.65–9.29, W = 6.86–7.91, Q’ = 1.1–1.4 (– 1.5), Q = 1.18–1.26, apiculus occasionally eccentric.

Distribution and ecology.

Africa ( Kenya); decorticated wood of deciduous trees.

Remarks.

Phylogenetically, P. nudum is closely related to P. galzinii (Fig. 2 ). It differs from the latter species in having wider, predominantly ellipsoid basidiospores and larger basidia. Moreover, basidial cells of P. nudum are often exposed, while they are normally rather deeply embedded in the layer of hyphidia in P. galzinii . Protohydnum nudum is known only from two collections from East Africa ( Kenya); the range of P. galzinii lies further to the north, stretching from Macaronesia to the Caucasus and Middle East Asia.

Figures

Figure 2. Bayesian majority-rule consensus ITS-based tree of the Protohydnum clade. Support values are given as Bayesian posterior probabilities. Basidiodendron spp. were used as an outgroup.

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.