Species with the largest cylindrical basidiospores ever observed in the genus (10.5–14.5 × 3.3–3.9 µm) and relatively large cystidia with prominent regular encrustation.

COSTA RICA. Cartago: Faldas del volcano Irazu, 1800 m, on decayed twig, 28 May 1991, L.Ryvarden (LR 29162 in O:F 506781).

grandisporum (Lat.), having large basidiospores.

Basidiomata annual, effused, resupinate, soft and fragile, arachnoid, thin, loosely adnate. Hymenophore smooth, finely velutinous due to numerous protruding cystidia, whitish. Margin thinning out, pruinose, adnate.

system monomitic. All septa with clamps. Subiculum thin, with loosely interwoven richly branched hyphae 3–4 µm wide, thin-walled, hyaline and smooth. Subhymenium thin, compact, with richly branched hyphae 3–3.5 µm wide, often covered with thin hyaline crystalline sheath. Cystidia subulate, 70–90 × 5–7 µm including encrustation, projecting up to 60 µm, without basal swelling, terminal or pleural, with thick hyaline cell wall and outer hyaline crystalline sheath covering the whole cystidium except the thin-walled, tapering apex. Crystal protrusions on cystidium are large, clearly rectangular to rounded, rather sparsely arranged in longitudinal rows.

Basidia suburniform, 13–19 × 5.5–7 µm, thin-walled, with 4 sterigmata and a basal clamp, often with hyaline crystalline collar at the base. Basidiospores cylindric, adaxial side slightly concave, L=(10–)10.6–14.5(–15.3) µm, W=(3.2–)3.3–3.9(–4.2) µm, Q= (2.9–)3.0–4.0, N=48/1, with minute apiculus, smooth, thin-walled, hyaline, negative in Melzer’s reagent.

Remarks on species. Until now, it is the only known Subulicystidium species with such large cylindrical basidiospores. Additionally, large cystidia with regular large protrusions, together with large basidia, make the species remarkable.