Protohydnum glabrum (Möller) 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

Protohydnum glabrum (Möller) Spirin comb. nov.

≡ Exidiopsis glabra Möller , Botanische Mittheilungen aus den Tropen 8: 168, 1895. Lectotype (selected here, MBT 10025861 ). Brazil. Santa Catarina, Blumenau , 8.II.1893 Möller 1039 ( HBG, studied).

Description.

Basidiocarps effused, covering a few cm, smooth, gelatinised, semitranslucent, dirty ochraceous to brownish, 0.1–0.2 mm thick, margin gradually thinning-out. Hyphal structure monomitic, hyphae hyaline, clamped; subicular hyphae indiscernible, subhymenial hyphae thin-walled, ascending, easily collapsing, 2.5–3.5 μm in diam. Gloeocystidia yellowish, tapering, embedded, 41–69 × 6.5–12 μm. Hyphidia abundant, richly branched, 1–1.5 μm in diam. at the apex, forming a continuous layer up to 20 μm thick. Basidia four-celled, longitudinally septate, ovoid-ellipsoid, pedunculate, 14.5–18 × 9.1–12.8 μm (n = 6 / 1), stalk up to 17 × 3–3.5 μm, sometimes strongly reduced, sterigmata gradually tapering, up to 12.5 × 3 μm. Basidiospores smooth, thin-walled, broadly ellipsoid to subglobose, 8.0–10.2 × 6.7–7.9 μm (n = 3 / 1), widely collapsed.

Remarks.

This species was described by Möller (1895) as a member of Exidiopsis from the southern part of Brazil and never mentioned thereafter. Here we reassess it based on the morphological study of the single remaining specimen in the HBG herbarium (designated as the lectotype above). The completely effused, smooth basidiocarps, abundant gloeocystidia, and ovoid-ellipsoid, clearly stalked basidia point towards Bourdotia galzinii (= Protohydnum galzinii in the present study) and satellite species as closest to P. glabrum . Among these species, P. nudum from East Africa looks most similar to P. glabrum . These species can be separated based on the length of gloeocystidia (twice as long in P. nudum compared to P. glabrum ) and the presence of distinct, thick epihymenial layer of hyphidia in P. glabrum . Protohydnum glabrum is so far known only from the type locality, and newly collected material is highly desirable to study it with DNA methods.