Chalciporus brunneus N. K. Zeng & X. Zhang sp. nov. Figs 2 f – h, 5 Etymology. Latin “ brunneus ”, referring to the pale brown to brown pileus. Holotype. China • Hainan Province, Changjiang County, Bawangling of Hainan Tropical Rainforest National Park, alt. 650 m, 19.2°N, 109.1°E, 13 May 2025, N. K. Zeng 8522 (FHMU 8246). Diagnosis. Differs from closest species of Chalciporus by a pale brown to brown pileus, a yellowish-white context unchanging when bruised, a yellow hymenophore, a stipe usually reddish at the apex, and an intricate trichodermal pileipellis. Description. Basidiomata very small to small-sized. Pileus 1.2–3.6 cm in diameter, subhemispherical to convex or plano-convex, margin incurved; surface slightly viscid when wet, pale brown to brown (6 C 2–6 C 3); context 0.2–0.7 cm in thickness in the center of the pileus, yellowish white (1 A 2), unchanging in color when bruised. Hymenophore poroid, slightly decurrent; pores roundish or angular, 0.15–0.25 cm wide, yellow (5 A 4), unchanging in color when bruised; tubes approximately 0.3 cm long, yellowish orange (5 A 5), unchanging in color when bruised. Stipe 1.8–3.8 × 0.3–0.65 cm, central, solid, subcylindrical; surface smooth, usually reddish at the apex, yellowish white (1 A 2) in the upper part, gradually becoming brown (6 B 2) toward the base, with distinct reddish longitudinal striations; context yellowish white (1 A 2), unchanging in color when bruised; basal mycelium white. Odor indistinct. Taste mild. Basidiospores [160 / 8 / 4] (7) 8–10.5 (11) × 3–5 μm, Q = (1.70) 1.90–3.00 (3.33), Q m = 2.34 ± 0.31, yellowish brown in KOH, elongated to cylindrical, slightly thick-walled (0.8–1 µm), smooth under the light microscope. Basidia 19–30 × 6–9 μm, clavate, slightly thick-walled (up to 1 µm), 4 - spored, colorless to pale yellow in KOH; sterigmata 2–4 μm in length. Cheilocystidia 33–65 × 5–11 μm, fusiform or subfusiform, slightly thick-walled (up to 1 µm), colorless in KOH. Pleurocystidia 33–71 × 6–9 μm, fusiform or subfusiform, slightly thick-walled (up to 1 µm), colorless in KOH. Hymenophoral trama boletoid, colorless to yellowish in KOH, thin- to slightly thick-walled (up to 0.5 μm), 4–10 μm wide. Pileipellis an intricate trichoderm 200–360 μm in thickness, composed of hyaline in KOH, slightly thick-walled (up to 1 µm) hyphae; terminal cells 8–69 × 4–8 μm, clavate to subcylindrical or cystidioid. Pileus trama made up of hyphae 4–20 μm in diameter, slightly thick-walled (up to 1 µm), colorless in KOH. Stipitipellis a trichoderm-like structure 150–300 μm thick, composed of hyaline to pale yellow in KOH, slightly thick-walled (up to 1 µm) hyphae; terminal cells 30–60 × 5–6 μm, clavate or subcylindrical, occasionally subfusiform. Stipe trama composed of parallel hyphae 3–13 μm in diameter, cylindrical, thin- to slightly thick-walled (up to 1 μm), hyaline to pale yellow in KOH. Clamp connections absent in all tissues. Habitat. Gregarious on the ground in forests dominated by fagaceous trees (Lithocarpus spp.). Known distribution. Southern China (Hainan Province). Additional materials examined. China • Hainan Province, Changjiang County, Bawangling of Hainan Tropical Rainforest National Park, alt. 650 m, 19.2°N, 109.1°E, 12 May 2025, N. K. Zeng 8522-1 (FHMU 11617); • same location and date, N. K. Zeng 8522-2 (FHMU 11547); • same location and date, N. K. Zeng 8522-3 (FHMU 11548). Notes. Chalciporus brunneus is phylogenetically related to C. aurantiolepidotus and C. hainanensis. However, C. hainanensis has a light orange-brown pileus, a white context turning red when bruised, and a reddish-orange hymenophore (see below). The morphological differences between C. brunneus and C. aurantiolepidotus have been discussed above. Morphologically, C. brunneus is similar to C. sinensis. However, C. sinensis has a pileus covered with brown to grey-brown scales, shorter, subglobose to ellipsoid basidiospores measuring 4–7 × 3.5–5 μm, and a trichodermial pileipellis (Xu et al. 2021).

Published as part of Zhang, Xu, Li, Xin-Ni, Liang, Wei-Qing, Mu, Xiao-Dong, Yu, Ye-Fei, Wu, Xiao-Jun, Chen, Si-Yu, Pu, Jin-Bao & Zeng, Nian-Kai, 2025, The subfamily Chalciporoideae (Boletaceae, Boletales) in China, pp. 123-157 in MycoKeys 124 on pages 123-157, DOI: 10.3897/mycokeys.124.165901