Leucoagaricus griseosquamosus Sysouph. & Thongkl.
Pileus 12–20 mm diam., umbonate, expanding to applanate with low umbo, with straight margin; squamose at umbo toward the margin, grey to grayish-brown (8F1–3), glabrous to slightly coarse and darker at the umbo, on a white background and turning reddish-white (7A2) when touched; margin with white fibrillose, sulcate when mature. Lamellae free, ventricose, 2–4 mm wide, white, turning reddish-white (7A2) when touched, moderately crowded, with a concolorous eroded edge. Stipe 23–33 × 2.5–3.5 mm, cylindrical, wider at base; covered with white fibrillose on white background, turning reddish-white (7A2) when touched. Annulus cuff-liked, white fibrillose, attached at the upper side of the stipe, fragile or disappearing when mature. The context in pileus white, up to 1 mm wide; in stipe hollow, white, with white fibrils in hollow; both pileus and stipe context turning reddish-white (7A2) when cut. Smell and taste not observed. Spore print white.
Basidiospores [75,3,3] l × w = 6.0–7.5 × 4.0–4.5 μm, avl × avw = 6.4 × 4.2, Q = 1.4–1.7, Qav = 1.5, in side-view ellipsoidal ovoid to oblong ovoid, in frontal view ovoid to oblong, slightly thick-walled, hyaline, dextrinoid, congophilous, cyanophilous, metachromatic. Basidia 14–17 × 7–8 μm, clavate, hyaline, thin-walled, 4-spored. Pleurocystidia absent. Cheilocystidia 14–25 × 7–11 μm, short clavate to clavate, sometimes fusiform, often septate, hyaline, slightly thick-walled. Pileus covering trichodermal made up of erect chains of ellipsoidal to oblong elements, 10–25 × 5–7.5 μm, with depression at septate, branched, with intracellular and parental brown to dark brown pigments, slightly thick-walled. Stipe covering a cutis made of cylindrical to narrowly clavate elements, 17.5–30 × 5.5–7.5 μm, hyaline, thin-walled, with hyaline hyphae, 2.5–10 μm wide. Clamp connection absent in all tissues.
Habitat and known distribution: growing solitary or with few basidiomata, saprotrophic and terrestrial on soil; found in deciduous forests during the rainy season of central and northern Laos.
Material examined: Laos, Oudomxay Province, Xay District, Houay HoumValley, collected date 23 Jun 2014, P. Sysouphanthong, PS2014-110 (HNL501781, holotype); ibidem, 08 Jul 2014, P. Sysouphanthong, PS2014-315 (HNL501986, paratype); Vientiane Capital, Xaythany District, Houy Nhang Preserve Forest, 17 Nov. 2015, P. Sysouphanthong, PS203(HNL503430, paratype).
Notes: Leucoagaricus griseosquamosus is commonly recognized by small and white basidiomata, squamose and grey to grayish-brown pileus, white lamellae, cylindrical and white fibrillose stipe, cuff-liked annulus, ovoid basidiospores, broadly clavate to utriform cheilocystidia and a trichodermal pileus covering, a cutis stipe covering. There are few species with grey color that are similar to Leucoagaricus griseosquamosus. Firstly; the European species, Leucoagaricus melanotrichus (Malençon & Bertault) Trimbach is the most similar to Leucoagaricus griseosquamosus by morphology; the type species was from Morocco, and described as Lepiota melanotricha Malençon & Bertault (Malençon & Bertault 1970). Leucoagaricus melanotrichus has a grey to dark grey background with purplish-brown squamulose fibrils on pileus, 15–20 μm mm diam.; stipe is white and with grey to the dark grey annulus; spores are ellipsoidal subamygdaliform, 6.0–7.5 × 3.8–5 μm; basidia are clavate, 23–26 × 7–9 μm; cheilocystidia are clavate to narrowly clavate, 25–45 × 7–13 μm; and a trichodermal pileus covering (Candusso & Lanzoni 1990). However, Leucoagaricus griseosquamosus is different in grey to grayish-brown squamose pileus with white background, white annulus, shorter basidia (14–17 × 7–8 μm), shorter cheilocystidia (14–25 × 7–11 μm) and sometimes with septate, and basidiomata are turned reddish-white when touched. Furthermore, the result from NCBI BLAST of the type species of Leucoagaricus griseosquamosus (MZ577104) showed that lacking identical species, and the analysis of nrITS sequence showed that two new sequences of Leucoagaricus griseosquamosus are identical, and are clustered with Leucoagaricus melanotrichus (AY176417) with low bootstrap support. Secondly, Leucocoprinus heinemannii Migl. is a species having black to dark grey fibrillose squamules on white background, but different from Leucoagaricus griseosquamosus by having distinctly sulcate-striate on pileus margin, and the species are known from temperate Europe (Birkebak 2010, Salom & Siquier 2017, Migliozzi & Zecchin 1998). Furthermore, Lepiota atrodisca Zeller is similar to Leucoagaricus griseosquamosus by having mouse grey to sooty black squamules on pileus and almost striate and splitting margin, white lamellae, equal and white stipe, superior and white annulus with blackish margin, ellipsoid-ovoid basidiospores (7 × 4 μm) and clavate cheilocystidia (Zeller 1938). However, Lepiota atrodisca has some similar characteristics and lacking clamp-connection; although it is placed in the genus Lepiota. Phylogenetically, Leucoagaricus tangerinus Y. Yuan & J.F. Liang is close to Leucoagaricus griseosquamosus. However, Leucoagaricus tangerines is distinguished by having light orange to brownish-yellow fibrillose on pileus (Yuan et al. 2014).
Fig. 1 Phylogenetic tree based on Maximum Likelihood analysis of nrITS sequences. Bootstrap values ≥ 60% are indicated above the branches, and Bayesian posterior probabilities ≥ 0.95 are placed above after ML bootstrap values. GenBank accession numbers are given after species names. The new sequences are in bold. Agaricus bisporus (J.E. Lange) Imbach, Chlorophyllum molybdites (G. Mey.) Massee and Macrolepiota dolichaula (Berk. & Broome) Pegler & R.W. Rayner were used as outgroups.