Butyriboletus brunneoides L. Fan & H.Y. Fu, sp. nov. 1 (Fig. 3)

Mycobank:—MB842144

Diagnosis:—differs from Bu. brunneus in the small to medium basidiome with a smooth pileus, a thin stipe that develops reddish stains at the base and the isolated phylogenetic position.

Etymology:—‘ brunneoides ’, refers to the similarity to Bu. brunneus .

Holotype:— CHINA. Shanxi Province, Jincheng City, Qinshui County, Shangwoquan village, 35°35ʹ1ʺN, 112°4ʹ37ʺE, elev. 1150 m, on the ground under Quercus spp ., 26 July 2021, collected by Jingchong Lv LJC045 (BJTC FM1816).

Description:— Pileus 3.5–9.4 cm in diam., hemispherical to convex, becoming broadly convex when mature; surface dry, smooth, yellowish brown (#ffbb78) to brown (# c96400), margin decurved; context firm and dense, thick, pale yellow (#ffff68) to yellow (#fffc9a), unchanging when exposed, or turning very slightly pale blue over the tubes. Hymenophore (tube layer) bright yellow (#ffff1a) to light yellow (# eaff80), changing blue when exposed; pores circular to somewhat elliptical, 0.2–0.3 mm in diam; tubes 2–5 mm deep. Stipe 4.5–6 × 0.7–3 cm, cylindrical, equal, widening towards the base, dry, solid, covered with a fine yellow reticulum; pale yellow (# eaff80), developing pale red stains near the base changing blue when bruised; annulus absent. Basal mycelium whitish (#ffffff) to pale yellow (#fff281). Odor distinct like salted fish when dry. Taste unpleasant, typically bitter or somewhat tart.

Basidiospores [40/2/2] 11–15(–17) × 3–5 [Q = 3.25–3.75 (4.33), Q m = 3.5 ± 0.25], subfusiform, subhyaline in KOH. Basidia 27.5(–15)–35 × 7.5–10 μm, clavate, thin-walled, 4-spored; sterigmata short. Hymenophoral trama boletoid. Pleurocystidia 35–45 × 8–12.5 μm, smooth, thin-walled, hyaline in KOH, fusoid-ventricose to broadly clavate with subacute apex; cheilocystidia 30–32.5 × 7.5–10 μm, smooth, thin-walled, hyaline in KOH, narrowly clavate to clavate-ventricose. Pileipellis an interwoven trichoderm 37.5–50 μm thick, composed of interwoven hyphae 2.5–5 μm in diam., hyphae yellowish brown (#edb849), hyaline in KOH, smooth, thin-walled, terminal cells cylindric with subglobose or rounded apices. Stipitipellis an interwoven trichoderm-like structure 105–200 μm thick, composed of thin- to slightly thick-walled (up to 1 μm) hyphae with narrowly or broadly clavate, subfusiform or fusiform terminal cells (16–26 × 4–9 μm), and some emergent hyphae with clavate or subcylindrical terminal cells. Stipe trama composed of cylindrical, thin to slightly thick-walled (up to 1 μm), parallel hyphae 3–14 μm diam. Clamp connections absent.

Habit, habitat and distribution: solitary or scattered, on ground in a Fagaceae forest, currently only known from Shanxi Province, North China.