Amphistereum schrenkii (Burt) Spirin & Malysheva, in Fungal Biology 121 (8): 696 (2017)
Diagnosis: Basidiocarps annual, cupulate-orbicular, leathery, up to 0.3 cm in widest dimension and up to 0.5 mm thick. Margin elevated, sometimes involute; abhymenial surface pale brown, azonate, densely hirsute. Hymenophore soft ceraceous, smooth, white to pale grey
Basidiospores broadly cylindrical, slightly curved, (11.0–) 11.8–14.3 (–15.0) × (5.9–) 6.0–7.1 (–7.2) µm (n = 30/1), L = 13.12, W = 6.51, Q = 2.02. Basidia ellipsoid-ovoid, four–celled, (15.2–) 17.8–31.2 (–35.3) × (9.8–) 10.0–13.5 (–14.0) µm (n = 20/1). Cystidia rather rare, narrowly clavate, some slightly tapering to the apex or indistinctly constricted, 31–49 × 5–7 µm. Hyphal structure dimitic; hyphae with clamp connections. Hyphae of abhymenial surface pale brown, thick walled, occasionally clamped, loosely arranged, subparallel, 4–6 µm in diam., CB (+), with accidental crystals. Skeletal hyphae pale to dark brown, very thick-walled, arranged in parallel bundles, often densely glued together, present in the uppermost part of context and producing more or less solid layer (visible under × 50 magnification as a dark brown line), 2–4 µm in diam., CB (+). Generative hyphae hyaline, with distinct walls, dominating in upper trama, interwoven and partly glued together, (2.2–) 2.4–4.2 (–5.2) µm in diam. (n = 20/1), CB (+), sometimes encrusted by scattered angular crystals. Subhymenial hyphae hyaline, thin- or slightly thick-walled, short-celled, vertically arranged, 2–4 µm in diam., occasionally inflated up to 6 µm. Hyphidia abundant, covering hymenial surface, richly branched, 2–3 µm in diam. at the apex.
Index Fungorum number: IF818019
Notes: Amphistereum schrenkii produces small-sized, cup-like basidiocarps with a pale-coloured hymenial surface. Its distribution is limited to arid regions of the US South-West (Arizona, New Mexico, Texas), where it occurs mostly on dead branches of mesquite (Prosopis spp.) (Burt 1915; Gilbertson et al. 1976 – as ‘Exidiopsis leucophaea’, Wells & Raitviir 1980).
Figure 1. Microscopic structures of A. schrenkii (Burdsall 8476): (A) hymenium; (B) basidia; (C) cystidia; (D) skeletal hyphae; (E) hyphae of abhymenial surface. Scale bar = 10 µm