Rhodophana hongshiensis T. Bau & Tian Y. Zhang sp. nov.

Figs 3 L, 11

Etymology.

The specific epithet “ hongshiensis ” refers to Hongshi National Forest Park, the origin of the type collection.

Holotype.

China. • Jilin Province, Huadian City, Hongshi National Forest Park, 22 September 2024, 42°50'56"N, 127°07'12"E, alt. 498 m, Wei-Nan Hou, H 2492218, (FJAU 75561).

Diagnosis.

The pileus light orange-yellow to broom yellow, centrally depressed, smooth, with translucent striations at margin. Lamellae adnexed, slightly crowded. Stipe smooth. Basidiospores ellipsoid to amygdaliform with pronounced undulate-pustulate ornamentation.

Description.

Basidiomata collybioid. Pileus diameter 0.4–0.9 cm, initially hemispherical, later convex. When fresh, light orange-yellow (RAL 1028), broom yellow (RAL 1032); when dry, ochre-yellow (RAL 1024). Pileus depressed at center, surface smooth; margin with translucent striations, slightly recurved. Context thin, ivory (RAL 1014); odor indistinct. Lamellae adnexed, sandy yellow (RAL 1002), ventricose, slightly crowded, unequally long. Stipe central, 1.6–2.7 cm long, 0.2–0.3 cm thick, subcylindrical, soil-brown (RAL 8003), slightly curved, solid; surface smooth.

Basidiospores.

[40 / 2 / 2] (6.3 –) 6.4–6.7 – 7.5 (– 7.7) × (3.9 –) 4.1–4.3 – 4.6 (– 4.7) μm, Q = 1.35–1.77, Q m = 1.57 (± 0.10), hyaline, ellipsoid to amygdaliform in profile view, ellipsoid in face view, obscurely angular in polar view, with undulate-pustulate surface ornamentation. Basidia 22–28 × 8–9 μm, clavate, 4 (2) - sterigmata. Cheilocystidia and pleurocystidia absent. Hymenophoral trama regular, composed of cylindrical hyphae 9–18 μm in diameter. Pileipellis a cutis, composed of cylindrical hyphae 9–16 μm in diameter, with pale yellowish pigment; terminal cells 38–77 × 12–23 μm, cylindrical, subfusoid. Stipitipellis composed of repent, cylindrical hyphae 6–11 μm in diameter, with yellowish-brown pigment. Clamp connections present in all tissues.

Habitat.

Solitary or scattered 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, 21 September 2024, 42°50'56"N, 127°07'12"E, alt. 498 m, Tolgor Bau and Tian-Yu Zhang, ZTY 2492107, (FJAU 75562).

Notes.

Morphologically, Rho. hongshiensis closely resembles Rho. nitellina (Fr.) Papetti in its orange-toned pileus with translucent striations. However, the latter can be distinguished by its significantly larger pileus (40–50 mm diam.) and larger basidiospores measuring 7.5–10 × 4.5–5.6 μm (Bas et al. 1988). Within the Rho. nitellina complex, a small-sized taxon, Rho. nitellina var. minor (Fr.) Papetti, has been documented. According to the taxonomic revision by Papetti, this entity was not elevated to species rank but was transferred from its previous placements in Agaricus and Collybia into Rhodophana, establishing the new combination Rho. nitellina var. minor (Fr.) Papetti. Compared to Rho. hongshiensis, Rho. nitellina var. minor possesses more robust basidiomata, a pileus with a more reddish-brown tinge, and grows gregariously on the ground in coniferous forests, allowing clear differentiation (Papetti 2014).

Rho. hongshiensis is phylogenetically closely related to Rho. almae - lunae Papetti; however, the latter can be distinguished by its basidiospores with rounded pustules and its primary distribution in coniferous forests (on litter of Pinus or Cedrus) (Papetti 2024). Compared to Rho. melleopallens (P. D. Orton) Kluting et al., the latter has larger basidiomata and smaller basidiospores (4.5–7.0 × 3–4 μm, Q = 1.3–1.4) (Bas et al. 1988). Rho. hongshiensis and Rho. aershanensis J. Z. Xu from the Inner Mongolia Autonomous Region of China both possess small basidiomata. However, the latter has a reddish-brown pileus and smaller basidiospores (2.7–5.8 × 2.2–5.1 μm, Q m = 1.1) with slightly undulate-pustulate surfaces (Xu et al. 2023).