MycoBank: MB838448

Etymology: The specific epithet “ subsphaerosporum ” refers to the shape of basidiospores.

Diagnosis: Differs from I. carnosibulbosum by having more globose basidiospores and clavate to cylindricalclavate cheilocystidia.

Type:— CHINA. Hainan Province: Ledong Li Autonomous County, Yinggeling substation of Hainan Tropical Rainforest National Park, 18°53ʹ27.21′′N, 109°19ʹ36.87′′E, elev. 400 m, 13 July 2020, L.-Y. Liu & Y.-G. Fan, FYG5848, FHMU3153 (holotype), GenBank nos.: MT 072898 (ITS), MT 071203 (LSU), MT 076849 (rpb 2).

Description:— Basidiomata medium-sized. Pileus conical when young, then convex to umbonate-convex, finally plano-convex to applanate with a subacute or occasionally obtuse umbo; margin initially incurved and then decurved for a long time, never straight; surface dry, initially smooth with a thin whitish veil layer around the disc, becoming appressed-scaly with radial patches of veil remnants, fibrillose-rimulose elsewhere, margin rimose to strongly split in age; yellowish brown (6C6) to chocolate brown (6E6) around the center, yellowish white (5A4) to beige (5A2) towards margin; uniformly brownish yellow (4A4) to goldish yellow (4A7) when overmatured. Lamellae crowded, adnexed, alternating with several tiers of lamellula, 2–4 (6) mm wide, dirty-white (5A1) or beige (5A2) at first, then grayish white (6B1) to brownish gray (6C2), brownish yellow (6B4) to brown (6D6) in age; edge pallid (5A1), fimbricate to finely serrate. Stipe 55–115 × 6–10 (12) mm, terete, equal at upper half with a slightly swollen apex, thicker downwards with a swollen base; recurved squamulose at the apex, longitudinally fibrillose with sparse protruding fibrils downwards, base pure white (6A1) with tomentose hyphae; ivory white (7A1) to grayish white (6B1), background brownish or pinkish beneath the cuticle. Context solid, fleshy in pileus, ivory white, with brownish (5C6) tinge under the umbo, becoming brownish (5D8) with age, 4–8 mm thick at the center, 2–3 mm thick at mid-radius; fibrillose and striate in the stipe, lightly brownish or pinkish (6B8). Odor slightly salty or mild.

Basidiospores [115/5/3] (5–) 6–7.5(–8) × 5–6(–6.5) μm, Q = 1.00–1.27 (–1.30), Q m = 1.13, subglobose to globose, occasionally broadly ellipsoid, smooth, yellowish or tan, indistinct small apiculus, inner with a large circular yellow oil-droplet. Basidia 26–31 × 7–8 μm, clavate to broadly clavate, occasionally obtuse at the apex and slightly tapering at the base, 4-spored, sterigmata 3–4.5 μm in length, hyaline to yellowish, with one or more bright yellow, oily inclusions when mature. Pleurocystidia absent. Cheilocystidia 27–50 × 8–11 μm, abundant, versiform, clavate, cylindricalclavate or occasionally broadly clavate to fusiform, often with obtuse apex, or narrowly tapered into capitate or subcapitate at the apex, septate and often constricted at septa, mostly thin-walled, some with walls up to 1 μm thick at the apex or towards the middle, colorless, at times with yellow intracellular contents. Hymenophoral trama 43–77 μm thick, regular to sub-regular, colorless to slightly yellowish, composed of cylindric to inflated hyphae 19–32 μm wide. Pileipellis a cutis, goldish yellow or tan, composed of sub-regular, thin-walled, yellowish, cylindrical hyphae, 7–10 μm wide, slightly encrusted. Stipitipellis regularly arranged, yellowish, disrupted with entangled, extended hyphae, 4–10 μm wide, terminal elements usually inflated to cheilocystidoid cells 39–62 × 10–21 μm, clavate to elongate or broadly clavate, hyaline, obtuse at the apex, occasionally capitate at the apex, thin-walled. Oleiferous hyphae 5–10 μm wide, present in pileus and stipe trama, yellow or bright yellow, smooth, bent, diverticulate, occasionally branched. Clamp connections present, common in all tissues.

Habitat: gregarious in small groups or scattered along roadsides under fagaceous trees.

Distribution: Known only from the type locality in Hainan Province, China.

Additional specimen examined: CHINA. Hainan Province, Ledong Li Autonomous County, Yinggeling substation of Hainan Tropical Rainforest National Forest Park, 18°53ʹ27.21′′N, 109°19ʹ36.87′′E, elev. 400 m, 13 Jul. 2020, under fagaceous trees, L.-Y. Liu & N.-K. Zeng, FYG5846 (FMHU 3155), Y.-G. Fan & L.-S. Deng, FYG5847 (FMHU 3154).