Inocybe carpinicola Y. G. Fan, W. J. Yu & P. M. He 2022, sp. nov.

Inocybe carpinicola Y.G. Fan, W.J. Yu & P.M. He sp. nov. Figs. 2–3

MycoBank: MB 845393

Holotype: — CHINA. Hainan Province: Wuzhishan City, Nansheng Town, Wuzhishan substation of Hainan Tropical Rain Forest National Park, on clay soil under Carpinus L. (1753: 998) forests, at 109°40′43′′E, 18°51′53′′N, 688 m asl., 30 July 2021, leg. W. J. Yu, P. M. He & Y. G. Fan, FYG6307 (FCAS3513); GenBank accession numbers: OP 207874 - ITS, OP 207868 - LSU, OP 227086 - rpb2.

Diagnosis: — This new species can be distinguished from other taxa in the genus Inocybe by brown, smooth- to striped-fibrillose, acutely umbonate, and small-sized pileus; subdistant lamellae with 10–13 attached to the stipe; slender stipes; nodulose to sub-stellate, 7.0–10.0 × 5.5–7.5 μm size basidiospores; sub-fusiform, utriform to clavate pleurocystidia mostly <50 μm in length; the absence of caulocystidia and oily hyphae, and association with Carpinus trees.

Etymology: — referring to its putative host plant, Carpinus londoniana var. lanceolata (Hand. - Mazz.) P. C.Li. (1979: 68).

Description: —Basidiomata small - sized, and slender. Pileus 3–12(17) mm, conical when very young, conicalcampanulate to convex or applanate with a small pointed umbo, occasionally not umbonate but with depression towards the disc when mature; margin slightly incurved, then straight upon maturity; surface dry, smooth-fibrillose to striped-fibrillose, covered with grayish-white (1 B 2) appressed velipellis in young specimens around the center, more sparsely so outwards, fugacious; initially dark brown (6 E 6–6 E 7), then yellowish brown (5 C 6) or brownish yellow (5 C 8), sometimes darker towards the margin (6 E 8). Cortina present at both pileus margin and upper part of stipe in young specimens, fugacious. Lamellae adnexed, sub-distant, 1–1.5 (2) mm in width, unequal with 10–13 attached to the stipe, alternately distributed with 3–4 tiers of lamellulae, edge indistinctly fimbricate, nearly concolorous with the face; white to ivory white (1 A 1–1 B 1) at first, then beige (1 B 2–1 B 3) to brownish (4 B 8), brown (5 B 7–5 C 8) to dark brown (6 C 7–6D8) when mature. Stipe 15–40 mm long, 0.8–1.5 mm wide, terete, solid, equal with a slightly swollen base, pruinose at the extreme apex, covered with a heavy partial veil and a dense appressed whitish vesture downwards, background pale yellowish (5 B 5–5 B 6) when young, brownish (5 B 7) at maturity. Context fleshy, white (1 A 1) to beige (1 B 2–1 B 3) with a brownish tinge (5 C 8) in pileus, 0.2–0.4 mm thick at mid-radius, 1–1.3 mm under the umbo; fibrillose in stipe, brownish (5 B 5), striate, shiny. Odour indistinct.

Basidiospores [100/4/2](7.0)7.5– 8.4 –9.2(10.0) × (5.5)5.8– 6.3 –7.0(7.5) μm, Q =(1.07)1.10– 1.32 –1.50(1.61), Q m ± SD =1.32 ± 0.0107; nodulose to sub-stellate, with 7–9 prominent nodules, apiculus small and indistinct, yellowish to goldish in 5% KOH, with one intracellular ellipsoid oily content. Basidia 20–28 × 7–11 μm, slenderly clavate to clavate, occasionally broadly clavate, obtuse at apex, tapered downwards, some with oily contents of different sizes, with 4- or 2- sterigmata 3–5 mm length, colorless or yellowish. Pleurocystidia 41–52 × 11–20 μm, sub-fusiform, utriform to broadly clavate, apices rounded or obtuse, often with crystals, base tapered into pedicel or occasionally truncate, slightly thick-walled, walls yellowish, 0.5–1 μm thick; colorless but with yellowish contents. Cheilocystidia 33–50 × 12–19 μm, resemble pleurocystidia, clavate or fusiform, walls yellowish, up to 1 μm thick. Hymenophoral trama 50–77 μm thick, sub-regularly arranged, yellowish in mass, composed of cylindrical or inflated hyphae measured 3–9 μm or 11–25 μm wide, respectively, smooth, colorless to yellowish, thin-walled. Pileipellis a cutis, 30–52 μm thick, brownish in mass, composed of cylindrical to inflated hyphae 4–20 in width, incrusted, thin-walled, walls yellowish. Pileal trama colorless or yellowish, sub-regular, hyphae inflated, colorless, 13–19 μm wide. Stipitipellis a cutis, regular, hyphae thin-walled, incrusted, and yellowish to yellow. Stipe trama regularly arranged, composed of colorless to yellowish, thin-walled, incrusted hyphae 4–15 μm wide. Caulocystida, cauloparacystidia, and oily hyphae not observed. Clamp connections present in all tissues.

Habitat and ecology: — Scattered on clay soil under Carpinus londoniana var. lanceolata . Fruits in July to August in tropical China.

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

Additional specimens examined: — CHINA. Hainan Province: Wuzhishan City, Nansheng Town, Wuzhishan substation of Hainan Tropical Rain Forest National Park, on clay soil under Carpinus forests, at 109°40′43′′E, 18°51′53′′N, 690 m asl., 29 July 2021, leg. Y.- G. Fan, L.- S. Deng, L.- N. Zhao, J.- H. Hu, FYG6297 (FCAS3617), FYG6300 (FCAS3618), 30 August 2021, leg. W.-J. Yu, P.-M. He, Y.-G. Fan, FYG6312 (FCAS3620), FYG6315 (FCAS3621), W.- J. Yu & Y.- G. Fan, FYG6381 (FCAS3622).