Cystostereum subsirmaurense S.L. Liu & L.W. Zhou, sp. nov.

Index Fungorum number: IF 901050; Mycobank number: MB 901050; Facesoffungi number: FoF 14805; Figs. 1, 2

Etymology – subsirmaurense (Lat.) referring to the similarity to Cystostereum sirmaurense.

Holotype – LWZ 20170618–10 (HMAS).

Diagnosis – Differing from C. sirmaurense in thick-walled, wider cystidia (Kaur et al. 2019).

Basidiomes annual, resupinate, effused, adnate, corky to hard and brittle, up to 20 cm long, 4 cm wide, 200 µm thick. Hymenophore smooth, with minute scattered tubercles, white when fresh, becoming yellowish white to orange white on drying. Margin thinning or indeterminate, concolorous or paler.

Hyphal system dimitic; generative hyphae with clamp connections, hyaline, thin-walled, 2–3 µm in diam; skeletal hyphae subhyaline, unbranched, 1–1.5 µm in diam. Cystidia subglobose to clavate, generally with an obtuse apex, thick-walled, with a basal clamp connection, embedded in hymenium and subhymenium, 30–50×7–15 μm. Basidia subclavate, 4-sterigmate, with a basal clamp connection, 15–20×5–6 μm. Basidiospores ellipsoid to subcylindrical, hyaline, smooth, thin-walled, IKI–, CB–, 3.5–4×2.6–3 µm, L=3.7 µm, W=2.8 µm, Q=1.3 (n=30/1).

Material examined – China, Yunnan Province, Xishuangbanna Dai Autonomous Prefecture, Jinghong, Mengla County, Xishuangbanna National Park of Tropical Rainforests, on fallen branch of angiosperm, 18 June 2017, L.W. Zhou, LWZ 20170618–10 (HMAS, Holotype).

GenBank numbers – ITS=OR557246, LSU=OR527272.

Notes – Cystostereum subsirmaurense is nested within the Cystostereum clade from a phylogenetic perspective (Fig. 3). Morphologically, this species is recognized by smooth hymenophore with minute scattered tubercles, which makes it similar to C. sirmaurense. However, C. sirmaurense differs in slightly thick-walled, narrower cystidia (7–8.5 µm in width, Kaur et al. 2019).

Figure 1 – Basidiomes of Cystostereum subsirmaurense (LWZ 20170618–10, holotype). Scale bars: a=1 cm, b=1 mm

Figure 2 – Microscopic structures of Cystostereum subsirmaurense (LWZ 20170618–10, holotype). a-b A vertical section of basidiomes. c Cystidia. d Basidia. e Basidioles. f Basidiospores. Scale bars: a=100 μm, b–f=10 μm

Figure 3 – Phylogeny generated by the maximum likelihood algorithm based on combined ITS and nLSU regions is presented along with the bootstrap values and the Bayesian posterior probabilities above 50% and 0.8, respectively, at the nodes. Holotypes are in bold and the newly generated sequences are in blue. Coniophora olivacea FP-104386 and C. puteana FP-105438 were selected as the outgroup taxa