Xanthagaricus siamensis

Xanthagaricus siamensis Yuan S. Liu & S. Lumyong

Index Fungorum number: IF556936; Facesoffungi number: 06314

Pileus 31–54 mm diameter, initially hemispherical to convex or subumbonate, then to plano-convex with depressed center, surface white, covering with greyish orange (5B6) to violet brown (11E4) fibrillose squamules with age; margin incurved with appendiculate white remnants. Lamellae free, fragile, with 3–4 lamellulae, crowed, with eroded edge, initially white, becoming pinkish (11A2) when injured, dull green (25D4) or dark green (25F8–6) with age. Stipe 35–65 × 2–6 mm, equal, central, cylindrical, slightly curved, hollow, white covered with greyish yellow (4C7), smooth to slightly fibrillose squamules. Annulus membranous, white, superior, attached to upper quarter of stipe, fugacious, often absent due to handling or as a consequence of age. Taste and smell not observed.

Basidiospores [75,3,3] 4.0–5.5 × 2.5–3.0 μm, avl × avw = 4.8 × 2.8 μm, Q = 1.45–1.97 μm, Qm = 1.73 ± 0.124, ellipsoid to oblong, smooth, yellowish white (4A2) to brownish orange (5C4), inamyloid, thin-walled, without germ pore. Basidia 10.5–15.0（–16.0）× 4.5–6.0 μm, clavate, hyaline, 4-spored, sterigata up to 2 μm long. Lamellar trama regular to subregular, composed of thin-walled, cylindrical hyphae 3.0–8.0 μm wide. Pleurocystidia absent. Cheilocystidia 11.5–22.5 × 4.5–10.0 μm, crowed, varying in shape from narrow clavate to broadly clavate, sometimes obovoid, hyaline, thin-walled. Pileipellis a cutis, composed of repent thin walled, 3.5–8 μm wide, subhyaline to brown hyphae with intracellular pigment as observed in KOH or H2O; terminal cells measuring 32.0–43.0 × 3.5–6.5 μm. Stipitipellis a cutis, made up of parallel, thin-walled, hyaline, 3.0–6.0μm wide hyphae. Clamp connections absent in all parts of basidioma.

Habitat and distribution: solitary or in small groups with few basidiomata, saprotrophic on soil in tropical deciduous forests, currently known to be indigenous only to Thailand.

Additional collections examined: THAILAND. Chiang Rai Province: Muang District, Mae Fah Luang University, N 20°3’11’’, E 99°53’19’’, alt. 400 m, 14 Oct 2018, Yuan S. Liu, STO-2018-76 (paratype: MFLU 19-0574 and isoparatype: HKAS 106212), ITS sequence GenBank MN176992 and nrLSU sequence GenBankMN176982. Tak Province: Phop Phra district, Chong Khaep, village, N 16°30’4’’, E 98°45’10’’, alt. 650 m, 18 Oct 2018, Yuan S. Liu, STO-2018-118 (paratype: MFLU 19-0576 and isoparatype: HKAS 106215); ITS sequence GenBank MN176993 and nrLSU sequence GenBank MN176983.