Leucoagaricus laosensis Sysouph.
Basidiomata small to medium size. Pileus 15–30 mm diam., convex to sub-umbonate with small umbo, expanding to applanate or slightly plano-concave with low center or umbo when mature, with straight margin; with very crowded fibrillose at center or umbo, light brown to dark brown (6E4–7, 6F6–8), around center with concolorous tuff, fibrillose or fibrillose squamules with uplift tip towards margin, with white to orange-white (5A2) fibrillose background; margin with concolorous fibrillose or fibrillose squamules, sulcate and fringed when mature, with or without white to light brown (6E4–5) remnants. Lamellae free, ventricose, 4–6 mm wide, crowded, white, with concolorous eroded edge. Stipe 25–35 × 5–8 mm, wider at base and tapering to apex, bulbous 12 mm wide, with white fibrillose background, sometimes with hyaline water drops, covered with light brown to dark brown (6E4–7) fibrillose squamules from middle to base, crowded at base. Annulus attached at middle or slightly high on stipe, membranous, white, hanging down, with light brown to brown (6E4–7) fibrillose squamules at edge. Context in pileus white, up to 3 mm wide; in stipe, white, hollow. Taste not observed. Spore print white. Basidiospores (50.2.2) 7.0–7.5 × 4.3–5 μm, avl × avw = 7.2 × 4.5 μm, Q = 1.4–1.70, Qav = 1.60, in side-view ellipsoidal to oblong ovoid, slightly amygdaliform with rounded apex, in frontal view ellipsoid to oblong, hyaline, thick-walled, dextrinoid, congophilous, cyanophilous, metachromatic. Basidia 17–20 × 7–8 μm, clavate, hyaline, thin-walled, 4-spored. Pleurocystidia absent. Cheilocystidia 20–30 × 5–10 μm, clavate to narrowly clavate, rarely cylindrical, hyaline, thin-walled. Pileus covering a trichoderm made up of cylindrical elements, terminal elements 40–90 × 12–15 μm, slightly thick-walled, with brown parental and intracellular pigments. Stipe covering a trichoderm made up of cylindrical elements, terminal elements 20–60 × 10–15 μm, slightly thick-walled, with brown parental and intracellular pigments. Clamp connections absent.
Habitat and distribution: Saprotrophic, on soil with rich humus, growing solitary or in small cluster with few basidiomata. The species is only known from northern Laos.
Material examined: LAOS, Oudpmxay Province, Xay District, Houay Houm Village, 23 July 2014, P. Sysouphanthong (HNL501802, holotype).
Notes: Leucoagaricus laosensis can be recognized by small to medium size, convex to sub-umbonate pileus and covered by light brown to dark brown fibrillose to fibrillose squamules, oblong to ellipsoidal ovoid basidiospores, clavate basidia, clavate to narrowly clavate cheilocystidia, and trichodermal structure of pileus and stipe covering. According to the colour of pileus covering, it is rare species related to Leucoagaricus laosensis. Leucoagaricus infuscatus from the USA, is similar to Leucoagaricus laosensis by the size of basidiomata (18–24 mm) and applanate to shallowly plano-convex pileus covered with brown fibrillose. However, Leucoagaricus infuscatus has distant lamellae, smooth stipe and whitish on watery pinkish-cream background, narrower basidiospores (5.6–7.6 × 3.4–4.4 μm), longer cheilocystidia (26–57 × 4.0–12 μm), a cutis structure of pileus covering (Vellinga 2007).