Inocybe motuoensis A. H. Zhu, W. J. Yu & Hai X. Ma, 2025

Zhu, An-Hong, Xu, Yan-Ru, Ma, Hai-Xia & Yu, Wen-Jie, 2025, Three nodulose-spored Inocybe (Agaricales, Basidiomycota) species discovered from Motuo, Southwest China, MycoKeys 122, pp. 99-121 : 99-121

Inocybe motuoensis A. H. Zhu, W. J. Yu & Hai X. Ma sp. nov.

Figs 4 , 5

Etymology.

Named after Motuo County, the type locality in Xizang Autonomous Region, China.

Holotype.

China • Xizang Autonomous Region: Motuo County, Beibeng Town , in sandy soil under tropical forest, alt. 1100 m, 8 September 2024, Hai X. Ma & A. H. Zhu, FCATAS 14059 (XZ 1389). GenBank accession numbers: ITS ( PV 827766 ); LSU ( PV 833643 ); RPB 2 ( PV 845801 ).

Diagnosis.

Basidiomata small, Pileus yellowish brown with pallid margins; lamellae subcrowded; stipe glabrous, cylindrical, with a swollen base. Basidiospores nodulose with 7–11 distinct blunt nodules; hymenial cystidia fusiform with a tapered base and usually forming a pedicel, walls slightly thickened, yellowish, Caulocystidia absent. Occurs in broad-leaved forests in tropical Xizang, China. Most similar to I. humilis , but differs from it by the larger basidiospores with more pronounced nodules, mostly fusiform hymenial cystidia with thinner walls (1–1.5 µm thick), the lack of caulocystidia, and an ecology in tropical forest.

Description.

Basidioma small. Pileus 12–15 mm in diameter, campanulate to nearly conical when young, becoming plano-convex at maturity, with a distinct umbo at the center; margin even, spreading; surface dry, radially fibrillose with fine cracks to splitting, nearly smooth, sometimes with slightly raised small scales; center of the pileus brown (5 B 4) to umber brown (5 C 7), gradually fading towards the margin, mostly light brown (5 B 3) to pale yellowish-brown (6 D 5), margin pale yellow (1 A 3). Lamellae adnexed, subcrowded, 0.8–1.3 mm wide, unequal in length, with 3–4 tiers of lamellulae, edge faintly serrate; white (1 A 1) when young, becoming grayish-white (1 B 2), and at maturity pale yellow (1 A 3) to yellowish-brown (4 B 6). Stipe 20–30 mm long, 1.6–2.3 mm thick, cylindrical, solid; base swollen but non-marginate, up to 2.6 mm thick; glabrous throughout, covered with whitish (1 A 1) tomentose hyphae at the base; pale yellow (1 A 3), pale pinkish-brown (6 C 4) to yellowish-brown (6 E 7). Context of the pileus fleshy, brownish (5 B 3) near the surface, otherwise white (1 A 1); stipe context fibrous, brownish (6 E 5). Odor faintly salty.

Spores [100 / 2 / 2] (8.1) 8.2–9.8 – 11.3 (12.1) × (6.5) 6.7–8.2 – 9.3 (10.1) µm, Q = (1.04) 1.06–1.20 – 1.40 (1.51), Qm ± Sd = 1.20 ± 0.1040, verrucose, with 7–11 distinct warts, yellow to yellowish-brown in 5 % KOH. Basidia 27–38 × 8–15 µm, subcylindrical to clavate, bearing 2–4 sterigmata, sterigmata 4–9 µm long, occasionally up to 13 µm, thin-walled, hyaline, with internal oil droplets, sometimes translucent. Pleurocystidia 51–59 – 68 × 15.5–19.4 – 24 µm (n = 30), mostly fusiform, broadly fusiform, or narrowly fusiform, occasionally sublageniform, apex mostly obtuse, sometimes subcapitate, often encrusted, constricted at the base to form a short stalk, thick-walled, 1–1.5 µm thick towards the middle, with walls gradually thickening from the base upwards, thickest at the apex (up to 2–3 µm), walls distinctly yellow, mostly hyaline and lacking contents, occasionally with pale yellowish internal contents. Cheilocystidia 31–38 – 46 × 17.5–19.4 – 22 µm (n = 30), similar to pleurocystidia, fusiform to narrowly fusiform, with thick walls up to 2–3 µm at the apex, walls distinctly yellow. Cheiloparacystidia 20–28 × 8–13 µm, abundant, broadly clavate to obovate, thin-walled, hyaline, translucent. Hymenophoral trama 38–54 µm thick, subregular, composed of cylindrical to broadly cylindrical hyphae, cylindrical hyphae 5–7 µm wide, broadly cylindrical hyphae 13–25 µm wide. Pileipellis an epithelium, 30–60 µm thick, brown to brownish, composed of elongated cylindrical hyphae, 4–10 µm wide, thin-walled, surface rough, pale yellow. Pileus trama subregular, composed of inflated hyphae, 15–24 µm in diameter, relatively smooth, thin-walled, hyaline, and colorless. Stipitipellis composed of elongated cylindrical hyphae, 3–10 µm in diameter, pale yellow, mostly smooth, occasionally rough. Stipe trama hyaline, composed of narrow cylindrical and broadly cylindrical hyphae, narrow cylindrical hyphae 3–7 µm wide, broadly cylindrical hyphae 10–20 µm wide, thin-walled, smooth, and colorless. Oleiferous hyphae commonly observed in the stipe and pileipellis, 4–13 µm wide, smooth-surfaced, with protruding nodules, pale yellow to yellow. Clamp connections present in all parts of the basidioma.

Habitat & distribution.

Gregarious in humus-rich soil under tropical rainforests; currently known only from the type locality in southeastern Xizang.

Additional specimens examined.

China • Xizang Autonomous Region: Same locality as holotype, 8 September 2024, Hai X. Ma & A. H. Zhu, FCATAS 14835 (XZ 1389 A). GenBank accession numbers: ITS ( PV 834867 ); LSU ( PV 834865 ); RPB 2 ( PV 847675 ) .

Remarks.

Inocybe motuoensis is characterized by a yellowish-brown pileus, a glabrous stipe with a submarginatae base, basidiospores with conspicuous protruding rounded nodules, and slightly thick-walled hymenial cystidia. Phylogenetically, the new species belongs to the I. xanthomelas group but shows no clear affinity to other taxa within this group. The Xanthomelas group comprises species with small to medium-sized, slender basidiomata featuring yellow-ochre pilei, initially whitish to pale yellow stipe bearing a marginate basal bulb, and an indistinct odor. Diagnostic traits include elongated cystidia (high length-to-width ratio) and age-related darkening caused by intracellular pigments (yellow, ochraceous, or dark brown) within hymenial elements (cystidia, basidia) and contextual hyphae. These pigments intensify in aged or dehydrated specimens, resulting in brown-grey to near-black discoloration, with interspecific variation in pigment concentration ( Esteve-Raventós et al. 2015). Inocybe motuoensis similarly exhibits darkening tissues due to pigmented cell walls in microstructures, consistent with the I. xanthomelas group. However, the absence of caulocystidia and presence of rounded nodules on basidiospores distinguish I. motuoensis within this species group.

Figures

Figure 4. Basidiomata of Inocybe motuoensis. a, b. XZ 1389 (holotype). Photos by A. H. Zhu. Scale bars: 10 mm (a, b).

Figure 5. Microscopic features of Inocybe motuoensis (XZ 1389, holotype). a, b. Basidiospores; c. Basidia; d, e. Cheilocystidia and cheiloparacystidia; f. Cross-section of pileus; g. Pleurocystidia; h. Pileipellis hyphae; i. Pileal tramra hyphae; j. Oily hyphae; k. Cross-section of lamellae; l. Stipitipellis hyphae; m. Stipe trama hyphae. Photos by J. Zheng. Scale bars: 10 μm (a – m).