Refer to the distinctive yellow and densely hairy (tomentose) surface of the mushroom’s pileus.

China • Xizang Autonomous Region: Linzhi City, Motuo County, in soil under tropical forest, alt. 1100 m, 21 July 2023, Hai X. Ma, FCATAS 9422 (XZ395). GenBank accession numbers: ITS (PV823515); LSU (PV833587); RPB2 (PV845799).

Inocybe flavitomentosa is characterized by small to medium-sized basidiomata with yellowish white to pale yellow coloration, a subtomentose pileus surface, crowded lamellae, a slender entirely pruinose stipe, angular-nodulose basidiospores bearing faint apical knobs, and abundant lageniform to fusiform hymenial cystidia. While morphologically similar to I. paludinelloides, it differs from it by its smaller basidiospores with less pronounced knobs, smaller hymenial cystidia, and an ecology in tropical broad-leaved forests.

Basidiomata: Small to medium-sized. Pileus 18–24 mm diam., hemispherical with decurved margin when young, becoming campanulate to parabolic, eventually broadly convex with a depressed to straight margin at maturity; surface dry, fibrillose to fibrillose-rimulose, finely subtomentose near margin; margin often splitting or strongly crenulate with age; coloration yellowish white (1A2) to pale yellow (2A2) or grayish white (2A1), darker toward the disc. Lamellae adnexed, crowded, alternating with 3–4 tiers of lamellulae, 0.8–1.5 mm wide; initially whitish yellow (1A2), maturing to pale yellow (2A3); edges entire to finely crenulate. Stipe 45–60 × 2.3–3.8 mm, central, solid, slightly swollen at apex and base; surface entirely white-pruinose (1A1), longitudinally striate, yellowish (2B3) to yellowish white (2A2). Context fleshy in pileus (0.5 mm thick at mid-radius, up to 2 mm under umbo), white (1A1); stipe context fibrous, yellowish white (2A2). Odor not recorded.

Basidiospores [n=100/2/2] (6.3–)6.5–7.8(–8.1) × (4.3–)4.6–5.8(–6.0) μm, Q = (1.18–)1.20–1.65 (Q_m = 1.39 ± 0.09), angular-nodulose with 8–11 low nodules, pale yellowish to yellowish brown in 5% KOH; apiculus indistinct; occasionally containing 1 circular to oblong oil droplet. Basidia 15–30 × 4–8 μm, clavate to narrowly clavate or subcylindrical, predominantly 4-spored (rarely 2- or 3-spored). Pleurocystidia (n = 40) 48–73 × 12–21 μm, lageniform to fusiform or sublageniform, occasionally cylindrical; apices crystalliferous, obtuse; walls thick (up to 2.5 μm), colorless to pale yellow; abundant. Cheilocystidia (n = 40) 38–60 × 12–18 μm, morphologically similar to pleurocystidia but predominantly fusiform; walls <3 μm thick. Cheiloparacystidia 10–20 × 4–8 μm, clavate to elliptical, thin-walled. Caulocystidia (n=30) 35–74 × 7–14 μm, fusiform to lageniform or cylindrical, thick-walled (up to 3 μm), descending entire stipe. Cauloparacystidia 15–23 × 3–9 μm, clavate, thin-walled. Hymenophoral trama subregular, 40–75 μm thick; hyphae 3–12 μm wide, thin-walled. Pileipellis two-layered: upper layer (72–125 μm thick) of interwoven, rough, thin-walled hyphae (2–5 μm); lower layer of yellow to yellowish brown, subinflated hyphae (7–14 μm). Stipitipellis a cutis of pale-yellow cylindrical hyphae (2–5 μm). Oleiferous hyphae present in stipe trama (2–6 μm). Clamp connections ubiquitous.

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

China • Xizang Autonomous Region: Same locality as holotype, 21 July 2023, Hai-Xia Ma, FCATAS 14838 (XZ395A). GenBank accession numbers: ITS (PV823516); LSU (PV834863); RPB2 (PV847673).

Inocybe flavitomentosa is a dull yellow species phylogenetically sister to the lineage comprising I. paludinelloides T. Bau & Y.G. Fan and I. spectabilis Y.G. Fan, L.W. Qin & B. Wang. Although similar in yellow coloration, I. paludinelloides differs in having larger basidiospores, larger hymenial cystidia, and an ecological preference for mixed Pinus-Castanopsis forests in subtropical montane regions (Chen et al. 2024). In contrast, I. spectabilis possesses larger, elongate basidiospores with more pronounced nodules, larger hymenial cystidia, pyriform cheilocystidia, and is associated with Betula in northeastern China (Chen et al. 2024). Another yellow-tinged species, I. danxiaensis, is distinguished by a non-tomentose pileus, greenish-yellow stipe, fusiform hymenial cystidia that never form a neck, and rough epicutis hyphae (Chen et al. 2024). Finally, the Australian species I. subangustifolia Matheny, Bougher & Halling, though dull yellow, has fusiform hymenial cystidia, occurs on sandy soils under Eucalyptus or Acacia, and occupies a distinct phylogenetic position (Matheny and Bougher 2017).

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

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 (XZ1389). GenBank accession numbers: ITS (PV827766); LSU (PV833643); RPB2 (PV845801).

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.

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 (5B4) to umber brown (5C7), gradually fading towards the margin, mostly light brown (5B3) to pale yellowish-brown (6D5), margin pale yellow (1A3). Lamellae adnexed, subcrowded, 0.8–1.3 mm wide, unequal in length, with 3–4 tiers of lamellulae, edge faintly serrate; white (1A1) when young, becoming grayish-white (1B2), and at maturity pale yellow (1A3) to yellowish-brown (4B6). 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 (1A1) tomentose hyphae at the base; pale yellow (1A3), pale pinkish-brown (6C4) to yellowish-brown (6E7). Context of the pileus fleshy, brownish (5B3) near the surface, otherwise white (1A1); stipe context fibrous, brownish (6E5). 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.

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

China • Xizang Autonomous Region: Same locality as holotype, 8 September 2024, Hai X. Ma & A.H. Zhu, FCATAS 14835 (XZ1389A). GenBank accession numbers: ITS (PV834867); LSU (PV834865); RPB2 (PV847675).

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.

Refers to the basidiospore morphology which is similar to I. chondrospora.

China • Xizang Autonomous Region: Motuo County, Bangxin Town, along Motuo Highway, in sandy soil under conifer-broadleaf mixed forest, alt. 2,429 m, 13 June 2024, leg. Hai X. Ma & A.H. Zhu, FCATAS 12445 (XZ1230). GenBank accession numbers: ITS (PV827765); LSU (PV833642); RPB2 (PV845800).

Basidiomata small, Pileus brown to reddish brown; lamellae subcrowded; stipe cylindrical with a swollen base, brown to reddish brown, entirely pruinose. Basidiospores oblong-ellipsoid to phaseoliform, regular; hymenial cystidia broadly fusiform with a tapered base and usually forming a short pedicel, walls thickened, yellow, Caulocystidia descending to stipe base. Occurs in broad-leaved forests in tropical Xizang, China. Most similar to I. chondrospora, but differs from it by an appressed-fibrillose to nearly glabrous pileus, smaller basidiospores, broader hymenial cystidia, and an ecology in subtropical evergreen forests.

Basidiomata small-sized. Pileus 15–20 mm diam., initially hemispherical to subglobose, becoming convex to plano-convex with age, developing a low obtuse umbo at maturity; margin persistently incurved in young specimens, decurved in age; surface dry, matte, radially striate near margin; disc umber (7B6) to chestnut brown (6E4), gradually fading to yellowish brown (5A5–6A6) towards margin. Lamellae adnexed, close, with 3–4 tiers of lamellulae; lamellar face brownish yellow (5D6) when dry, developing sparse dark brown (5E4) maculations; edges fimbriate, concolorous with faces. Stipe 15–19 × 2–3 mm, eccentric, terete, solid; surface densely white-pruinose (1A1) at apex, becoming fibrillose-striate downwards; apex strong brown (6E7) with punctate protrusions, gradually transitioning to brown (6B6) at base. Context fleshy in pileus, 2–3 mm thick at dis, fibrillose in stipe; yellowish white overall, developing brownish tones near stipe base. Odor not distinctive.

Basidiospores [100/2/2] (holotype) mostly ellipsoid to oblong-ellipsoid, (9.5)10.1–11.4–12.9(13.4) × (5.9)6.0–6.6–7.2(8.1) μm, Q = (1.3)1.5–1.7–1.9(2.0), Q_m ± SD = 1.73 ± 0.134; less often phaseoliform, 9.5–10.9–11.9 × 5.9–6.5–8.1 μm; smooth, yellow-greenish in KOH, containing 1–2 yellowish refractive oil droplets. Basidia 14–18–22 × 6–7–9 μm (n=30), predominantly clavate to cylindrical, 4-sterigmate (occasionally 2-sterigmate); sterigmata 2–8 μm long; contents yellowish with granular inclusions. Pleurocystidia 41–49–59 × 17–21–27 μm (n=30), fusoid-ventricose with broad basal pedicels (3–5 μm wide), walls thickened apically (2–4 μm), yellow-green in KOH. Cheilocystidia 40–46–60 × 11–22–25 μm (n = 30), morphologically similar to pleurocystidia. Cheiloparacystidia 9–14–20 × 8–11–15 μm (n = 30), clavate, thin-walled, hyaline. Hymenophoral trama regular, 38–72 μm wide; hyphae cylindrical to inflated (7–30 μm diam.), thin-walled, yellowish. Pileipellis 48–130 μm thick, cutis-type; hyphae parallel, 7–24 μm diam., walls yellowish brown with encrusted pigments. Stipe trama composed of parallel, cylindrical hyphae 6–14 μm diam. Caulocystidia 38–42–47 × 14–17–20 μm (n = 30), fusoid, thick-walled (2–3 μm), concentrated at stipe apex. Oleiferous hyphae present in all tissues, 3–12 μm diam., bright yellow, irregularly contorted. Clamp connections abundant throughout all tissues.

Gregarious in sandy soils of subalpine zone (2,400–2,500 m elev.); currently known only from the type locality in southeastern Xizang, also found in subtropical evergreen broad-leaved forests in Hubei province.

China • Xizang Autonomous Region: Motuo County, Bangxin Town, along Motuo Highway, in sandy soil under conifer-broadleaf mixed forest, alt. 2,429 m, 13 June 2024, leg. Hai X. Ma & A.H. Zhu, FCATAS 14836 (XZ1230A); GenBank accession numbers: ITS (PV834866); LSU (PV834864); RPB2 (PV847674) • Hubei Province: Yichang City, Wufeng Tujia Autonomous County, 17 June 2024, in subtropical evergreen forests dominated by fagaceous trees, Y.P. Ge, Q. Na, J.W. Guo, G.Y. Qiu & L.J. Wang, NJ5283 (FCAS4254). GenBank accession numbers: ITS (PV834856); LSU (PV834860).

Inocybe subchondrospora is distinguished by small, reddish-brown to cinnamon-brown basidiomata, a convex to plano-convex pileus, and pruinose stipes with a swollen but non-marginate base. Microscopically, it exhibits ellipsoid to elongate basidiospores with obtuse apices and broadly fusiform hymenial cystidia bearing small pedicels. Phylogenetically, I. subchondrospora forms a sister lineage to the north temperate taxon I. chondrospora (syn. I. immigrans Malloch), with this clade itself sister to I. kuberae Bandini & B. Oertel.

Inocybe chondrospora resembles the new species in basidiomata coloration and spore shape but differs in having a tomentose-scaly pileus, significantly larger basidiospores, larger hymenial cystidia (pleurocystidia: 38–80 × 11–28 µm), and an ecological preference for sandy soils associated with Betulaceae, Orchidaceae, Pinaceae, and Salicaceae (Dovana et al. 2023). In contrast, I. kuberae shares the dark brown pileus and pruinose stipe but diverges in nodulose spores (avg. 11.8 × 8.9 µm), ventricose (sub)lageniform hymenial cystidia, and occurrence on calcareous soils at subalpine elevations (Bandini et al. 2022).