Xanthagaricus necopinatus Iqbal Hosen, T.H. Li, and G.M. Gates in Hosen, Song, Gates, Karunarathna and Li
Index Fungorum number: IF 820482; Facesoffungi number: FoF 07068.
Pileus 10–20 mm, first paraboloid, expanding to convex, plano-convex, with or without umbo, with straight or slightly incurved margin; when young covered with crowded squamules, greyish-yellow to yellow (3B3–8), with brownish-yellow squamules (5C7–8) at center; when mature with yellowish-white to yellow (3A2–6) squamules on yellowish-white to pastel yellow (3A2–4) background; margin with concolorous squamules as on pileus surface and with light-orange (6A4–5) appendiculate velar remnants. Lamellae, l = 3 series, free, 2–4 mm wide, yellowish-white to orange-white (4A2, 5A2) when young, becoming orange-grey to greyish-orange (5B2–3) when mature, broadly ventricose, with white, eroded edge. Stipe 20–45 × 2–3 mm, cylindrical, white fibrillose at apex zone, with yellowish-white to yellow (3A2–6) squamules below annulus to base, with orange-grey to greyish-orange (5B2–3) background, turning greyish red (7B4–5). Annulus attached to the apical zone of the stipe, membranous, greyish-orange (6B4–6), sometimes fragile with age. Context white to orange-white (5A2) in pileus, up to 2 mm thick at the center; hollow in stipe and concolorous with the surface. Odor and taste not observed. Spore pint not observed.
Basidiospores [75,3,3] 4.0–5.2 × 2.5–3.5 µm, avl × avw = 4.71 × 2.90 µm, Q = 1.42–1.80, avQ = 1.62, ellipsoid to oblong-ovoid in frontal view, ellipsoid to oblong in side-view, thickwalled, smooth, hyaline to pale-brown, without a germ pore. Basidia 15–20 × 4.5–7 µm, short clavate to clavate, thin-walled, hyaline, 4-spored. Pleurocystidia absent. Cheilocystidia 17–25 × 5–10 µm, short clavate to clavate, often ellipsoid, with 1 or 2 septa at the base, slightly thick-walled, hyaline. Pileus covering an irregular epithelium composed of oblong to short clavate elements in the upper layer, 10–20 × 5–15 µm, with irregular globose to subglobose elements in the lower layer, 5–15 µm wide, slightly thick-walled, rough-walled, encrusted, with pale-brown to brown parietal and intracellular pigments, with hyaline to brown rough-walled and encrusted, up to 8 µm wide hyphae at base of the epithelial layers. Stipe covering an epithelium similar to that on pileus. Clamp connections absent.
Habitat and distribution: growing in large groups, saprotrophic on humus-rich soil with dead leaves and wood under trees or in grassland; commonly found in Chiang Mai and Chiang Rai Provinces, northern Thailand.
Material examined: Thailand, Chiang Mai Province, Muang District, Chiangmai University Campus, 28 July 2018, P. Sysouphanthong, PS2018-56 (MFLU 19-2353); Chiang Rai Province, Muang District, Forest of Mae Fah Luang University Campus, 8 June 2019 P. Sysouphanthong, PS2019-45 (MFL 19-2358); ibidem, 8 August 2019, P. Sysouphanthong, PS2019-67 (MFL 19-2359).
Notes: Xanthagaricus necopinatus has the slender basidiomata characteristic for the genus, and a pale-yellow pileus and stipe with squamules, velar remnants on the pileus margin, hyaline to pale-brown basidiospores, clavate to ellipsoid cheilocystidia, and an irregular epithelium on pileus and stipe; clamp-connections are absent. The basidiospores are smooth. Xanthagaricus necopinatus was originally described from Bangladesh, and this is the first report of this species outside that country. Thai specimens completely resemble the type specimens, but the stipe covering of type specimens is a cutis while the Thai specimens have an epithelium on the stipe. However, the nrITS sequences of Thai specimens are clustered with the type specimens with high BS. Xanthagaricus necopinatus can be confused with X. flavosquamosus T.H. Li, Iqbal Hosen and Z.P. Song, described from China, but differs from that species in the smoother pileus and the smooth (vs. rough) basidiospores. The differences in the width and shape of the cheilocystidia as mentioned by Hosen et al., are not supported by the data from the Thai collections.