Index Fungorum number: IF 552904; Facesoffungi number: FoF2950
Pileus 8–17 mm, at first parabolic to broadly convex, expanding umbonate with low umbo, inflexed margin; with warts, or pyramidal squamules, larger at centre and smaller towards margin, brown and turning dark brown (6F5–8, 6E4–6), on orange-white (5A2) background; margin cortinate in young samples, squamulose, fibrillose. Lamellae free, crowded, ventricose, 1.5–2 mm wide, white, yellowish-white when mature, with white serrulate edge. Stipe 28–32 × 1.8–2 mm, cylindrical, with bulb, 2.2–2.4 mm wide, completely floccose or with crowded squamules from annular zone toward base, light brown (6D5–6), white to yellowish-white (4A2) at apex, hollow. Annulus an annular zone, floccose or squamulose, light brown (6D5–6). Context white in pileus; white in stipe. Smell and taste not observed. Spore print white. Basidiospores  4–5 × 2.8–3 μm, avl × avw = 4.3 × 3 μm, Q = 1.1–1.6, Qav = 1.4, oblong ovoid in side-view, oblong in frontal view, thick-walled, hyaline, not dextrinoid, congophilous, cyanophilous, not metachrometic. Basidia 10–12.5 × 4–5 μm, clavate, 4-spored. Lamella edge sterile. Cheilocystidia 10–22 × 4–9 μm, clavate, narrowly clavate, rarely utriform, hyaline, thin-walled. Pileus covering an epithelium made up of several chains elements, terminal elements 10–25 × 7–17 μm, globose to ellipsoid, clavate, subclavate, with brown walls, slightly thick-walled; under layer with hyaline hyphae, cylindrical, up to 4 μm wide. Clamp connections present.
Habitat and distribution: growing solitary or in small groups, saprotrophic on rich humus soil, sand or loamyclayey, nutrient-rich soil.
Material examined: THAILAND, Chiang Mai Province, Mae Rim District, Mae Sa Valley, 12 July 2008, P. Sysouphanthong (MFLU 12-2036, holotype).
Notes: Lepiota microspila, a species from Sri Lanka is similar to L. maerimensis in its ochraceous tawny to rufous squamules on the pileus and stipe covering. Lepiota microspila differs from L. maerimensis in having a smaller spore size (3.3–4.5 × 1.7–2.3 (3.8 × 2) μm, shorter Basidia (6.5–8 × 3.3.5 μm), and thicker wall of elements in the pileus covering (up to 1 μm). Unfortunately, Cheilocystidia of Lepiota microspila were not recovered in the Sri Lankan material (Pegler 1972). Some species of section Echinatae from India are compared with this species, for example Natarajan and Manjula (1982) described Lepiota subrufa from South India and it differs from L. maerimensis in its pale red background on the pileus and stipe, and reddish-brown pyramidal squamules, pastel red Lamellae and dull red membranous annulus. Lepiota babruka is also similar to L. maerimensis in having brown to dark brown pyramidal squamules on the pileus, but it differs in lacking a squamulose stipe and yellowish-white to pale yellow lamellae (Arun Kumar and Manimohan 2009) (Fig. 2).
Fig. 1 Bayesian tree based on ITS sequence alignment of Lepiota species represent from each section. Support values from Bayesian posterior probabilities values (BYPP) more than 0.95 are given above tree branches, and bootstrap percentage more than 50% from maximum likelihood analyses are indicated below the tree branches. New sequences from Thailand are as bold. Agaricus bisporus and Clarkeinda trachodes are outgroup taxa
Fig. 2 Lepiota maerimensis (MFLU 12-2036, holotype). a Basidiocarps. b Basidiospores. c Basidia. d Cheilocystidia. e Pileus and stipe covering
Tibpromma S, Hyde KD, Jeewon R et al. 2017 – Fungal diversity notes 491–602—taxonomic and phylogenetic contributions to fungal taxa. Fungal diversity, 83(1), 1–261.