Megalocystidium effusum S. H. He 2025, sp. nov.

Megalocystidium effusum S.H. He, sp. nov. MB 843407. Figs 10F, 12. Etymology: The species epithet “ effusum ” refers to the effused basidiomes. Typus: China, Yunnan Province, Kunming, Yeyahu Park, on fallen angiosperm branch, 22 Aug. 2015, S.H. He, He 2526 (holotype BJFC 020979, isotype in BJM). Basidiomes annual, resupinate, effused, adnate, inseparable from the substrate, coriaceous, first as small colonies, later confluent up to 5 cm long, 2 cm wide, 100–150 µm thick. Hymenophore smooth, pale orange (5A3), light orange [5A(4– 5)] to greyish orange [5B(3–6)], turning light brown in KOH, uncracked; margin thinning out, slightly fimbriate, indistinct, concolourous with hymenophore. Hyphal system monomitic; all hyphae without clamps. Subiculum indistinct; hyphae colourless, slightly thick-walled, smooth, rarely branched, moderately septate, more or less parallel to substrate, 2.5–5 µm diam. Subhymenium distinct; hyphae colourless, thin- to slightly thick-walled, smooth, densely interwoven, 2–3.5 µm diam. Cystidia of three kinds: (1) pseudocystidia scattered, subclavate to subcylindrical, with a papilla at the apex, colourless to pale yellow, slightly thick-walled, smooth, mostly embedded, up to 100 µm long, 7–10 µm wide; (2) acutocystidia numerous, subulate, colourless, thin-walled, smooth, 15–20 × 3–4.5 µm; (3) acanthohyphidia clavate or hyphoid, with few to many spines at the apex, colourless, thin-walled, 18–26 × 3.5–6 µm. Basidia cylindrical to clavate, colourless, slightly thick-walled toward the base, with 4 sterigmata and a basal simple septum, 30–35 × 4–4.5 µm; basidioles dominant, in shape similar to basidia, but slightly smaller. Basidiospores oblong ellipsoid to subcylindrical, colourless, thin-walled, smooth, amyloid, acyanophilous, 7.5–10 × 2–3.5 µm, L = 8.4 µm, W = 2.9 µm, Q = 2.9 (n = 30/1). Additional specimen examined: China, Yunnan Province, Kunming, Yeyahu Park, on fallen angiosperm branch, 22 Aug. 2015, S.H. He, He 2514 (BJFC 020967, CFMR). Notes: Megalocystidium effusum is characterized by resupinate and pale yellow basidiomes, papillate pseudocystidia and numerous acanthohyphidia. Megalocystidium wakullum is similar to M. effusum by sharing resupinate basidiomes, presence of three kinds of cystidia and same size of basidiospores but differ in having longer acutocystidia (20–40 µm), less distinctly papillate pseudocystidia and a distribution in southern USA (Burdsall et al. 1981, Boidin et al. 1997). Moreover, the two species are recognized as independent lineages in the phylogenetic tree (Fig. 1).