Protohydnum Möller

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 Möller , Botanische Mittheilungen aus den Tropen 8: 173, 1895, emend.

= Bourdotia (Bres.) Bres. & Torrend , Brotéria Serie Botanica 11: 88, 1913. Type species. Sebacina galzinii Bres. (selected by Clements and Shear 1931: 342).

= Ductifera Lloyd , Mycological Writings 5: 711, 1917. Type species. Ductifera millei Lloyd .

= Gloeotromera Ervin , Mycologia 48: 692, 1956. Type species. Exidiopsis alba Lloyd .

Description.

Basidiocarps cushion-shaped – cerebriform or completely resupinate, with adnate or elevated margin, gelatinous; hymenial surface nearly smooth or (in one species) distinctly hydnoid. Hyphal structure monomitic, hyphae clamped. Gloeocystidia present in most species, tubular, variably tapering upwards, usually embedded. Basidia strictly four-celled, sessile (cerebriform species) or predominantly pedunculate to petiolate (resupinate species), with rather thick, distinctly located sterigmata. Basidiospores thin-walled, cylindrical to ellipsoid, more rarely cylindrical-subfusiform or broadly ellipsoid – subglobose, repetitive.

Type species.

Protohydnum cartilagineum Möller.

Here we redefine Protohydnum and merge it with Ductifera and Bourdotia . Additionally, two species earlier included in Exidiopsis (Bref.) Möller s. lato (i. e., Exidiopsis glabra Möller and E. livescens ) are also reclassified into Protohydnum . In its current scope, the genus contains sixteen species.

Phylogenetically, the large Protohydnum clade is the sister lineage of Basidiodendron Rick ( Weiß and Oberwinkler 2001, Spirin et al. 2020, 2021, present study – Fig. 1 ). All Basidiodendron spp. have gloeocystidia similar to those of the cystidiate Protohydnum species. However, the genera are quite different otherwise. Basidiocarps of Basidiodendron spp. are waxy-arid (not gelatinous as in Protohydnum ), and they become somewhat gelatinised at the very end of their development in only a few species. Furthermore, turgid basidia of Basidiodendron spp. are usually located at the very top of the basidia-bearing hyphae covered by remnants of already collapsed basidial cells, giving these structures a peculiar “ fishbone ” - like appearance; no such structures have been observed in Protohydnum spp. Moreover, basidiospores of Basidiodendron spp. feature a large, often asymmetrical, and somewhat eccentric apiculus (at least in the core species of the genus, i. e. those from the Basidiodendron eyrei (Wakef.) Luck-Allen and Basidiodendron caesiocinereum (Höhn. & Litsch.) Luck-Allen complexes) ( Spirin et al. 2020, 2021). In contrast, the basidiospore apiculus in Protohydnum spp. is, as a rule, rather small, regularly outlined, and conventionally located.

Figures

Figure 1. Bayesian majority-rule consensus ITS + LSU-based tree of the Auriculariales overlaid with bootstrap support values from the maximum likelihood analysis. Support values are given as Bayesian posterior probabilities / ML bootstrap percentages. Species with stalked basidia are marked with a red X. I – Protohydnum clade; II – Elmerina clade; III – Hydrophana clade; IV – Endoperplexa – Mycostilla clade; V – Protoacia – Gelacantha clade; VI – Protomerulius clade; VII – Myxarium clade. The Sebacinales (Ditangium P. Karst., Sebacina, and Serendipita P. Roberts spp.) and Exidiopsis gloeophora were used as outgroups.