Pileus 12–36 mm in diam., 2 mm thick at disc, hemisphaerical, extending broad conic, convex with broad umbo and deflexed margin in most cases, some without umbo; surface dry, glabrous to fibrillose, lacking squamules, generally white or cream, disc light orange, brownish orange (6C5), fading to margin, margin exceeding. Lamellae free, less crowded than usual for the genus or slightly distant, intercalated with lamellulae, 4–5 mm broad, ventricose, at first greyish brown (7D2, 7D3), then brownish grey, finally dark brown. Stipe18–80 × 2–4 (apex) –4–5 (base) mm, cylindrical to subclavate, hollow or stuffed with rhizomorphs at the base, white to slightly grey, smooth above the annulus, tomentose below the annulus and almost strigose towards the base, not staining on touching. Annulus membranaceous, superous, pendent, simple, fugacious, white, with radiate striations, up to 4 mm broad. Context firm, white both in pileus and stipe of young basidiomes, and grey to yellowish brown in stipe for mature basidiomes, colour unchanging on exposure. Odour of carbolic acid or ink. Macrochemical reaction: KOH reaction positive brightly yellow, Schäffer’s reaction negative. Basidiospores 5.5–6.5 × 3.2–4 μm [x = 6 ± 0.2 × 3.8 ± 0.3, Q = 1.4–2, Qm = 1.61 ± 0.39, n = 20], cymbiform to ellipsoid, smooth, thick-walled, with a slightly apical, endospore thickening, without a germ pore, reddish brown. Basidia13–18 ( − 22) × 4 – 7 μ m, hyaline, smooth, 4-spored. Cheilocystidia12–32 × 7–16 μm, pyriform, broad-clavate, smooth, hyaline. Pleurocystidia absent. Pileipellis a cutis consisted of hyphae 4–9 μm in diam., light yellow or hyaline, smooth, branched, not constricted at the septa. Annulus consisting of the same hyphae as pileipellis. (Figs. 1–2)
Index Fungorum number: IF 570197, Mycobank: 570197, Facesoffungi number: FoF01178
Etymology: epithet “lamellidistans” refers to the distant lamellae of this species, which is not common in most Agaricus species.
Holotype: Thailand, Chiang Mai Prov., Mae Taeng Dist., Tung Joaw village, forest trail, N19°08.07′ E98°38.90′, elev. 1300 m., 5 September 2006, collected by Ruilin Zhao, ZRL3099 (BBH 19615, holotype; HMAS 274007, isotype).
Habitat: solitary or scattered in small groups in red soil.
Specimens examined: THAILAND, Chiang Mai Prov., Mae Taeng Dist., Tung Joaw village, forest trail, N19°08.07′ E98°38.90′, elev. 1300 m., 5 September 2006, collected by Ruilin Zhao, ZRL3099 (BBH 19615, holotype; HMAS 274007, isotype). THAILAND, Chiang Mai Prov., Doi Suthep-Pui National Park, Sangasabhasri Lane to Huai Kok Ma village, N18°48.62′ E98°54.60′, elev. 1145 m., 2 July 2005, collected by Thanh Huyen Le, ZRL2081 (BBH 19464; HMAS 274013); same location, 7 June 2006, collected by Thanh Huyen Le, ZRL3034 (BBH 19550); same location, 13 June 2006, collected by Todd Osmundson, ZRL3063 (BBH 19579; HMAS 274004); Chiang Mai Prov., Mae Taeng Dist., Tung Joaw village, forest trail, N19°08.07′ E98°38.90′, elev. 1300 m., 30 June 2006, collected by Ruilin Zhao, ZRL3074 (BBH 19590; HMAS 274012); same location, 5 September 2006, collected by Ruilin Zhao, ZRL3098 (BBH 19614; HMAS 274020).