Myxarium inconspicuum (Pat.) 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 inconspicuum (Pat.) Spirin comb. nov.

Fig. 8 F

≡ Tremella inconspicua Pat. , Bulletin de la Société Mycologique de France 9: 138, 1893. Holotype. Ecuador. Pichincha: Quito (surroundings) , dead wood, II. 1892 Lagerheim ( FH 00060386 , studied).

Description.

Basidiocarps first pustular, 0.2–0.4 mm in diam., then fusing together and forming a compound basidiocarp, up to 5 mm in widest dimension, indistinctly tuberculate, gelatinous, opalescent, whitish, 0.1–0.2 mm thick, in dry condition hardly visible, margin sharply delimited, adnate. Hyphal structure monomitic, hyphae hyaline, clamped; subicular hyphae totally collapsed, subhymenial hyphae thin-walled, ascending, 1.5–2.5 μm in diam. Hyphidia abundant, richly branched, 1–2 μm in diam. at the apical part, scattered among basidia and partly covering basidial cells. Basidia four-celled, longitudinally septate, ellipsoid to broadly ellipsoid, pedunculate, (8.1 –) 8.3–9.2 (– 10.6) × (6.2 –) 6.5–8.2 (– 8.6) μm (n = 20 / 1), stalk up to 15 × 2–2.5 μm, sterigmata up to 7 × 1.5 μm. Basidiospores smooth, thin-walled, narrowly ellipsoid to ellipsoid or more rarely cylindrical, (5.0 –) 5.7–8.2 (– 8.9) × (3.4 –) 3.6–5.0 (– 5.1) μm (n = 30 / 1), L = 6.99, W = 4.30, Q’ = (1.3 –) 1.4–2.0 (– 2.2), Q = 1.63.

Remarks.

Tremella inconspicua was described from Ecuador ( Patouillard and Lagerheim 1893), and its connection with Myxarium was discussed by Spirin et al. (2019 b). We restudied the type specimen of T. inconspicua and are fairly confident that it belongs to Myxarium . Both macroscopically and anatomically, M. inconspicuum is similar to the European Myxarium grilletii (Boud.) D. A. Reid ; it differs from the latter species in having predominantly narrowly ellipsoid spores with a convex ventral side, while in M. grilletii (European specimens) the spores are mainly cylindrical or broadly cylindrical and often somewhat curved. However, the North American specimens of M. grilletii studied and illustrated by Spirin et al. (2019 b) possess predominantly ellipsoid basidiospores. An ITS sequence obtained from the Canadian specimen of M. grilletii (GenBank MK 098896 , designated as Myxarium aff. grilletii in Fig. 5 ) is identical with an unnamed sequence from the USA (GenBank KX 193945), and they clearly deviate from M. grilletii sequences from Europe. They may therefore represent a separate species and may in fact be conspecific with M. inconspicuum . Answering this question is not feasible without access to newly collected and sequenced material from Ecuador. Myxarium guianense introduced above differs from M. inconspicuum by its smaller discrete basidiocarps, slightly narrower basidiospores, and the presence of cystidia.

Figures

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 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.