Mycostilla chromatica Spirin & Grebenc, 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

Mycostilla chromatica Spirin & Grebenc sp. nov.

Figs 6 B , 8 D

Holotype.

Slovenia. Kočevje: Podstenice, Rajhenavski Rog , Abies alba (fallen decorticated log), 21. VIII. 2021 Spirin 14839 * ( H, isotype – LJF) .

Etymology.

Chromaticus (Lat., adj.) – chrome-yellow, in reference to the basidiocarp’s colour.

Description.

Basidiocarps effused, first small, then fusing together and reaching up to 20 cm in longest dimension, indistinctly or clearly tuberculate, gelatinous, semitranslucent, containing numerous chrome-yellow grains, 0.1–0.4 mm thick, drying to a bright-yellow thin crust, margin gradually thinning out. Hyphal structure monomitic, hyphae hyaline, clamped, richly encrusted by chrome-yellow angular crystals occasionally fusing together in large amorphous concretions; subicular hyphae thin-walled or with a distinct wall, interwoven, anastomosing, 2–4 μm in diam. (occasionally inflated up to 6 μm in diam.), subhymenial hyphae thin-walled, quickly collapsing, interwoven, 2–3 μm in diam. Cystidia absent. Hyphidia scattered, simple or sparsely branched, 1–1.5 μm in diam. at the apex. Basidia four-celled, longitudinally septate, broadly ellipsoid to globose, pedunculate, (8.3 –) 8.7–11.0 (– 11.2) × (7.8 –) 8.0–9.0 (– 9.2) μm (n = 20 / 2), stalk usually distinct, up to 15 × 2–3 μm, sterigmata gradually tapering, up to 20 × 1.5–2 μm. Basidiospores smooth, thin-walled, ellipsoid to broadly ellipsoid or subglobose, more rarely globose, (4.2 –) 4.7–6.1 (– 6.2) × (3.6 –) 3.8–5.2 (– 5.4) μm (n = 60 / 2), L = 5.20–5.31, W = 4.46–4.78, Q’ = (1.0 –) 1.1–1.3 (– 1.4), Q = 1.09–1.20, often with a large central oil drop.

Distribution and ecology.

Europe ( Slovenia); fallen decorticated logs of conifers ( Abies ).

Remarks.

Mycostilla chromatica is a distinctive species due to its brightly coloured, effused, and gelatinous basidiocarps. It has been found twice in the pristine fir-beech forests of Slovenia. The colours of M. chromatica are strongly reminiscent of the corticioid fungus Flavophlebia sulfureoisabellina (Litsch.) K. H. Larss. & Hjortstam ( Agaricales Underw. , Basidiomycota). The latter species also occurs on Abies alba logs in old-growth forests of Central Europe. However, it has thicker basidiocarps than M. chromatica and is microscopically completely different.

Figures

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.