Cystoderma microsporum R.L. Zhao, B. Cao & J.Xin Li [as ‘microspora‘], in Cao et al., Fungal Diversity 132: 560 (2025)

Index Fungorum number: IF 571119; MycoBank number: MB 571119; Facesoffungi number: FoF 17671; Figs. 1, 2

Etymology – “microspora”(Latin), made up of “micro-” meaning “small” and “spora” meaning “spore,” referring to the relatively small basidiospores of this fungal species.

Holotype – HMAS 288006.

Pileus 20–40 mm in diameter at a young stage, hemispherical, then becoming convex to plano-convex at maturity, surface dry, yellowish-ochre, yellowish-brown, darker toward the disc, covered with granular warts and fine powdery texture, with radially acute rugose, less prominent when mature, the margin incurved at first, then applanate when mature, often separates from the partial veil, yellowish-ochre to yellowish-white. Lamellae adnate, whitish, crowded, with 1–2 lamellulae of different lengths, less than 2 mm broad, straight. Stipe 40–70 × 6–10 mm, cylindrical, yellowish ochre yellowish-brown, with an evanescent floccose-scaly ring zone, yellowish brown and silky striate above the ring zone, below the ring zone yellowish-ochre to pale yellow, attached with numerous small granular furfuraceous squamules. Odor and taste are undocumented.

Basidiospores (2.8–)3.3–4.1(–4.7) × (2.3–)2.6–3.3(–3.7) µm (x̄ = 3.7 ± 0.4 × 2.9 ± 0.3, Q = 1.2–1.4, Qm = 1.3 ± 0.1, n = 30), globose to subglobose, smooth, hyaline, thin-walled, without a germ pore, inamyloid. Basidia 20.5–28.0 × 5.8–7.2 µm, clavate, smooth, hyaline and thin-walled, 4-spored. Pleurocystidia and cheilocystidia absent. Pileipellis on the upper layers composed of chains of numerous sphaerocytes, globose to subglobose, ellipsoid, thick-walled, with internal brown pigment, the lower layers composed of tightly interwoven hyphae, the composition of the evanescent floccose-scaly ring zone and pileipellis is identical. Clamp connections present in all tissues.

Habitat – Gregarious and saprobic on mixed coniferous-broadleaf forest, found among Abies balsamea, Rosa spp., and alpine Rhododendron spp. at elevations of approximately 2,500 m.

Materials examined – CHINA, Hubei Province, Shen nongjia Forest District, Shennongding Area, Jinhouling, 25 August 2022, Rui-Lin Zhao, ZRL20220873 (HMAS 288006, holotype) and ZRL20220874 (HMAS 288007).

GenBank – HMAS 288006: PV389792 (ITS), PV389800 (LSU); HMAS 288007: PV389793 (ITS), PV389801 (LSU).

Notes – Phylogenetic analyses based on ITS and nrLSU sequences indicate that Cystoderma microspora and C. subglobisporum form a fully supported lineage distinct from other Cystoderma species. This lineage is phylogenetically closest to C. simulatum (Fig. 1). All three species have relatively small basidiospores compared to other Cystoderma species. For instance, basidiospores measure 3.6–4.3 × 3.2–3.7 µm in C. subglobisporum and 3.5–5 × 2.5–3.5 µm in C. simulatum (Saar 2012; Kibby and Harding 2016; Li et al. 2022a). However, C. simulatum can be distinguished by its dark brick-red to cinnamon-red coloration and its highly wrinkled, puckered cap surface. Additionally, it grows in woodchip mulch under hazel and birch and fruits strictly in winter (Saar 2012; Kibby and Harding 2016). Cystoderma subglobisporum, recently described from the Xizang Autonomous Region in China, has a yellowish buff to yellowish-ochre pileus. Morphologically, it is distinguished by a distinct central papilla, a strongly radially acuterugose surface, and an inflexed margin (Li et al. 2022a).

Figure 1 – Maximum Likelihood tree of Cystoderma inferred from ITS and nrLSU sequences data, rooted with Crucibulum leave. Branches supported by both BS = 70% and PP = 0.90 were labeled. The examined specimens in this study are bolded.

Figure 2 – Cystoderma microspora. a Basidiomata (HMAS 288006, holotype). b Basidiomata (HMAS 288007). c Basidiospore. d Basidia. Scale bars: a–b = 1 cm, c–d = 5 µm.