Xanthagaricus latiannulus R.L. Zhao & J.X. Li, sp. nov. Fig. 12 Chinese name: 宽环黄蘑菇 (Pinyin: kuān huán huáng mó gū) Fungal Names registration: FN 572557
Etymology: From the Latin latus/i broad, wide and annu lus ring, annulus, by its broad annulus.
Type: China, Jiangsu Province, Nangjing City, Xuanwu District, Zijin Mountain, 4 Oct. 2023, X. Chen, ZRL20236230 (holotype HMAS 282450).
Diagnosis: Xanthagaricus latiannulus is distinguished by its small basidioma and surface covered with yellow ish to cherrywood brown or coffee-bean brown squamules. The species has a distinct membranous broad annulus, ellipsoid smooth basidiospores, and clavate to broadly clavate cheilocystidia.
Macroscopic description: Basidioma small to medium. Pileus 24–44 mm in diameter when mature, hemispherical when young, becoming plano-convex with age, with a whit ish to pale yellowish background, covered with squamules more or less flaky at center, cherrywood brown to coffee bean brown, densely and darker at center, elsewhere with small scales or fibrillose-squamulose, becoming lighter towards margin; with lacerated velar remnants that are con colorous with the squamules at margin; context white when fresh, not changing colour on damage. Lamellae free, close to crowded, depressed around the stipe, broadly ventricose in the middle, grayish to grayish brown, pale brownish, with 3–4 tiers of lamellulae, with smooth to slightly eroded mar gin. Stipe 30–55 × 4–7 mm, cylindrical to subcylindrical, sometimes tapering downwards to base; surface slightly grayish, whitish, with scattered small grey to greyish-white squamules or fibrils. Annulus, membranous, easily detach able and fragile, with yellowish brown or brownish squam ules on the underside that are concolorous with the pileus. Odor and taste unknown.
Microscopic description: Basidiospores [73/2/2], (4.1)4.3–4.9(5.3) × (2.7)2.9–3.5(4.7) μm, X = 4.6 ± 0.3 × 3.2 ± 0.3 µm, Q = 1.36–1.5, Qm = 1.4 ± 0.1, ellipsoid to broadly ellipsoid, slightly thick-walled, smooth, pale yellow to yellowish brown in H2O and 5% KOH, with a small apiculus, without germ pore. Basidia 13.2–18.5 × 5.4–7.3 μm, clavate, thin-walled, hyaline, 4-spored, occasionally 2-spored. Cheilocystidia 13.6–22.8 × 6.9–12.1 µm, abundant, clavate to broadly clavate, hyaline with thin walls. Pileus covering an irreg ular epithelium, composed of agglutinated globose to subglobose, rarely clavate to ellipsoidal cells, vertically arranged, 10.9–22.5 × 7.3–15.3 µm, pale-brown to brown with thin walls in H2O and 5% KOH. Clamp connections absent in all tissues.
Habitat and distribution: Typically, caespitose, found in humus-rich soil in broadleaf forests, such as Castanea for ests. Currently, known only from Jiangsu Province, China.
Additional material examined: China, Jiangsu Province, Nangjing City, Xuanwu District, Zijin Mountain, 4 Oct. 2023, X. Chen, ZRL20236160 (HMAS 282449).
Notes: Phylogenetic analyses based on four loci (ITS, nrLSU, rpb2, and tef1) indicate that X. latiannulus and X. montgomeryensis form a sister clade with X. taiwan ensis and X. thailandensis (Fig. 4). Morphologically, all species in this clade share yellow–brown basidioma with dark brown to fuscous-black squamules at the center, yellowish brown toward the margin. Basidiospore mor phology can successfully differentiate these species. Xan thagaricus montgomeryensis has slender basidiospores measuring (3.94) 3.99–4.87 (4.91) × (2.06) 2.12–2.85 (2.96) μm (average 4.35 × 2.47 μm), with Q = 1.65–1.93 (average Q = 1.75) (Fatima and Khalid 2023), compared to X. latiannulus, which has broader basidiospores: (2.7) 2.9–3.5 (4.7) μm wide (X = 3.2 ± 0.3 μm, Q = 1.36–1.5, Qm = 1.4 ± 0.1). Xanthagaricus taiwanensis and X. thai landensis can be distinguished by their larger basidi ospores. In X. taiwanensis, basidiospores measure (4.5) 5–5.5 (6) × 3–4 (4.5) μm (average 5.18 × 3.58 μm, Q = 1.33–1.67, average Q = 1.46 ± 0.09) (Ge et al. 2008), whereas in X. thailandensis, basidiospores are 6 − 7.5 × 4 − 4.5 μm, with Q = 1.33 − 1.75 (average Q = 1.56 ± 0.14) (Kumla et al. 2018).
