The species with the smallest basidiospores known in the genus, 5.0–6.2 × 2.2–2.8 µm and allantoid, combined with rather small cystidia with regular delicate encrustation.

RÉUNION. Saint-Pierre: Cilaos, Cirque de Cilaos, Roche Merveilleux, Sentiere botanique, 1300 m, -21.1232, 55.4920, on strongly decayed wood, 15 Mar 2013, E.Langer (L 0140 in FR; isotype in KAS).

parvisporum (Lat.), having small 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 1.8–3 µm wide, thin-walled, hyaline and smooth. Subhymenium thin, with hyphae similar to those in subiculum but occasionally bearing slight amorphous hyaline encrustation. Cystidia subulate, 45–65 × 2.5–3 µm including encrustation, projecting up to 30 µm, without basal swelling, terminal or pleural, with thin hyaline cell wall and outer hyaline crystalline sheath covering the whole cystidium except the thin-walled, narrow, acuminate apex. Crystal protrusions on cystidium are low but clearly rectangular and arranged in longitudinal rows.

Basidia suburniform to almost clavate, 10–15 × 4–5 µm, thin-walled, with 4 sterigmata and a basal clamp, occasionally with slight amorphous hyaline encrustation at the base. Basidiospores allantoid, often with a slight constriction in the middle part, L= (4.3)5.0–6.2(–6.8) µm, W=(1.8–)2.2–2.8(–3.0) µm, Q=(1.8–)1.9–2.6(–3.1), N=151/4, with minute apiculus, smooth, thin-walled, hyaline, occasionally with one or two oil drops, negative in Melzer’s reagent. Tolerance limits for basidiospore length, width and length to width ratio in S. parvisporum, based on 4 sequenced specimens, are provided in the Table 2.

RÉUNION. Saint-Benoit: Saint-Benoit, Forêt Margarithe, ca. 450 m, -21.1031, 55.6926, on dead wood, 24 Mar 2015, J.Riebesehl (L 1226 in FR and KAS). Saint-Pierre: Cilaos, Cilaos XII-87, forêt de la Mare à Joseph, au-dessus du hameau de Bras Sec, 1400 m, -21.1239, 55.4957, on dead wood, 4 Apr 1987, G.Gilles (LY 12750); le Tampon, Notre dame de la Paix, Forêt de la Riviere des Remparts, Sentier Botanique, -21.2559, 55.5987, on dead wood, 23 Mar 1998, E.Langer & E.Hennen (GEL 5032 in KAS).

Boidin and Gilles (1988) mentioned one collection with such small spores for his S. allantosporum ad interim (LY12750). After examining and sequencing the specimen, we conclude that it clearly represents our new species S. parvisporum. Both ours and specimens of Boidin and Gilles originate exclusively from Réunion.