Rhodocybe eburneolutea T. Bau & T. Y. Zhang sp. nov.

Figs 3 J, 3 K, 10

Etymology.

The specific epithet “ eburneolutea ” refers to the ivory to yellowish coloration of the pileus, derived from the Latin ‘ eburneus ’ (ivory-colored) and ‘ luteus ’ (yellow).

Holotype.

China. • Jilin Province, Huadian City, Hongshi National Forest Park, 23 August 2024, 42°50'56"N, 127°07'12"E, alt. 498 m, Tolgor Bau and Xian-Yan Zhou, Y 2482316 (FJAU 75556).

Diagnosis.

The pileus is ivory to beige, centrally depressed, and brown beige. The pileus surface is smooth and translucent striate. The basidiospores are subellipsoid to obscurely angular, ornamented with bumpy undulate-pustulate. The pseudocystidia are abundant, predominantly subfusoid to rostrate, rarely branched, and non-dextrinoid. Both the hymenophoral trama and the pileipellis are non-dextrinoid.

Description.

Basidiomata clitocyboid. Pileus diameter 0.4–1.1 cm, initially hemispherical, later applanate, depressed at center; when fresh beige (RAL 1001) to ivory (RAL 1014), center brown beige (RAL 1011); when dry ochre brown (RAL 8001), clay brown (RAL 8003). Pileus surface smooth, translucent striate; margin entire. Context thin, off-white (RAL 1013); odor indistinct or not distinctive. Lamellae adnate to subdecurrent, off-white (RAL 1013) to bright ivory (RAL 1015), slightly crowded, unequally long, fragile. Stipe central, 0.7–1.4 cm long, 0.2 cm thick, cylindrical, equal, hollow, ivory (RAL 1014) to yellow ochre (RAL 1024), slightly flexuous; surface smooth.

Basidiospores.

[80 / 4 / 3] (5.3 –) 5.5–6.0 – 6.6 (– 6.7) × (3.9 –) 4.0–4.4 – 4.7 (– 5.0) μm, Q = 1.20–1.49, Q m = 1.37 (± 0.08), hyaline, subellipsoid and somewhat rounded angular in profile view, broadly ellipsoid in face view, obscurely angular in polar view, ornamentation strongly bumpy undulate-pustulate. Basidia 20–25 × 6–7 μm, clavate, 4 (2) - sterigmata. Cheilocystidia (pseudocystidia) 23–41 × 4–7 μm, subclavate, narrowly lageniform, with a rarely branched apex, with golden pearl contents, non-dextrinoid. Pleurocystidia (pseudocystidia) 18–36 × 4–7 μm, flexuous, subcylindrical, subfusiform, with golden pearl contents, non-dextrinoid. Hymenophoral trama regular, composed of cylindrical hyphae 4–10 μm in diameter, non-dextrinoid. Pileipellis a cutis, composed of cylindrical hyphae 5–7 μm in diameter, with pale yellowish-brown pigment, non-dextrinoid. Stipitipellis composed of repent, cylindrical hyphae 3–5 μm in diameter, with yellowish-brown pigment. Clamp connections absent in all tissues.

Habitat.

Gregarious on the ground in mixed forests during summer.

Distribution.

Currently known only from Jilin Province, China.

Additional specimens examined.

China. • Jilin Province, Huadian City, Hongshi National Forest Park, 23 August 2024, 42°50'56"N, 127°07'12"E, alt. 498 m, Tian-Yu Zhang, ZTY 2482307 (FJAU 75557); • Same location, 15 September 2025, Yu-Fei Han, F 25915027 (FJAU 75571).

Notes.

Morphologically, R. eburneolutea is similar to R. asyae E. Sesli & Vizzini from Turkey, as both possess small, clitocyboid basidiomata with an ivory-colored pileus. However, the latter differs in lacking striations on the pileus surface, lacking pseudocystidia, and in its classification within sect. Rufobrunnea, allowing clear distinction (Sesli and Vizzini 2017). R. eburneolutea also shares a yellowish pileus and a slender stipe with R. zijinshanensis S. P. Jian & X. Chen from Nanjing, China, but R. zijinshanensis can be distinguished by its complete absence of hymenial cystidia and its distinct ecology of growing solitarily on rotten wood in broad-leaved forests (Jian et al. 2025).

Phylogenetically, R. eburneolutea is sister to R. caelata (Fr.) Maire (rpb 2: KC 816934). However, Kluting et al. (2014) have demonstrated that R. caelata as presently understood is polyphyletic with ambiguous species boundaries. This study reveals significant morphological differences between the new species and the polyphyletic R. caelata: the latter has more robust basidiomata, a grayish pileus that is velutinous and lacks translucent striations, larger basidiospores (7.0–9.0 × 4.0–5.0 µm, Q m = 1.75), and pseudocystidia that are mostly cylindrical to clavate (Baroni 1981; Bas et al. 1988). R. eburneolutea is also phylogenetically close to R. pakistanica Z. Khan & Khalid from Pakistan; nevertheless, R. pakistanica differs in its dark reddish-brown pileus, a stipe surface covered with white fibrils, and scarce pseudocystidia (Khan and Khalid 2024).