Myxarium guianense Gruhn & 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

Myxarium guianense Gruhn & Spirin sp. nov.

Figs 6 C , 8 E

Holotype.

French Guiana. Régina: Noruragues, Saut Pararé , decorticated log on the ground, 3.XII.2018 Gruhn GUY 18-559 * ( LIP, isotype – H).

Etymology.

Guianensis (Lat., adj.) – originating from French Guiana.

Description.

Basidiocarps first appearing as small pustules, 0.03–0.05 mm in diam., then fusing together and forming a compound basidiocarp, up to 3 cm in widest dimension, indistinctly tuberculate, gelatinous, opalescent, greyish, 0.1–0.2 mm thick, in dry condition vernicose, hardly visible, margin sharply delimited, adnate. Hyphal structure monomitic, hyphae hyaline, clamped, frequently anastomosing; subicular hyphae with a distinct wall, interwoven or subparallel, 1.5–5 (6) μm in diam., often slightly inflated at septa, subhymenial hyphae thin-walled or with a distinct wall, tightly glued together, ascending or interwoven, 1–4 μm in diam. Cystidia rare, distinctly tapering to almost subulate, 16–26 × 5.0–8.4 μm (n = 5 / 1), projecting up to 15 μm above hymenial layer. Hyphidia richly branched, 1–1.5 μm in diam. at the apical part, scattered among basidia. Basidia four-celled, longitudinally septate, ellipsoid to broadly ellipsoid, pedunculate, (7.7 –) 7.8–9.4 (– 9.7) × (6.5 –) 6.6–7.2 (– 7.3) μm (n = 20 / 1), stalk distinct although sometimes strongly reduced, up to 10 × 2–2.5 μm, sterigmata gradually tapering, rarely bifurcate, up to 10 × 1.2–1.5 μm. Basidiospores smooth, thin-walled, narrowly ellipsoid to cylindrical, the longest spores often slightly curved, (5.4 –) 5.6–7.3 (– 7.8) × (3.0 –) 3.1–4.1 (– 4.4) μm (n = 36 / 1), L = 6.65, W = 3.71, Q’ = (1.4 –) 1.5–2.1 (– 2.3), Q = 1.80.

Distribution and ecology.

South America ( French Guiana); decorticated angiosperm wood.

Remarks.

Morphologically, M. guianense is most similar to the European Myxarium minutissimum (Höhn.) Spirin & Trichies. However , the initially pustulate basidiocarps of M. guianensis fuse together completely and produce a crustaceous continuous one, while in M. minutissimum they fuse only partly, and therefore the compound basidiocarps have a very characteristic reticulate shape. Moreover, M. guianense differs from M. minutissimum in having cystidia. Phylogenetically, these species are not closely related (Figs 1 , 5 ). Differences between M. guianense and M. inconspicuum are discussed under the latter species. Myxarium guianense is so far known from the type locality in French Guiana.

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.

Figure 5. Bayesian majority-rule consensus ITS-based tree of the Myxarium clade. Support values are given as Bayesian posterior probabilities. Myxarium crystallinum was used as an outgroup.

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.