Phaeocollybia dingjieensis R. Y. Li & S. M. Tang 2026, sp. nov.

Phaeocollybia dingjieensis R. Y. Li & S. M. Tang sp. nov. Figs 2 A – C, 3 A, 3 B, 4 Chinese name. 定结暗金钱菌 (Ding Jie An Jin Qian Jun). Etymology. The specific epithet “dingjieensis” refers to Dingjie County, Xizang Autonomous Region, China, where the holotype was collected. Diagnosis. Phaeocollybia dingjieensis is distinguished by a light orange pileus with dark orange vertical stripes, a long hollow stipe turning dark desaturated red at maturity, limoniform basidiospores (7.6–9.2 × 4.6–5.8 μm) with verruculose ornamentation (apex and apiculus smooth), and the absence of pleurocystidia. Clamp connections occasionally. Holotype. China • Xizang Autonomous Region, Dingjie County, Chentang Town, elev. 3,332 m, 25 July 2025, Rui-Yu Li (HKAS 154723!). Description. Pileus 1.5–2.5 cm diam, paraboloid to broadly conical with acute papilla in center, margin subinvolute and subundate edge, mostly light orange (# ffce 77), margins dark moderate orange (# a 36 c 55), dark moderate orange vertical stripes over the surface, pileus context thin, 0.1–0.2 cm thick, slightly desaturated orange (# b 38769). Lamellae ventricose, adnexed to narrowly adnate, moderately close together, edge undate, 3–5 irregularly arranged tiers, 2–3 mm wide, light grayish yellow (# f 4 eed 6). Stipe central, cylindrical, hollow, 8–10 cm long, 0.2–0.3 cm diam, smooth in surface, soft orange (# edc 0 af) when young, becoming dark desaturated red (# 55373 b) at maturity, stipe context concolorous with pileus context. Pseudorhiza 1–4 cm long, hollow, rhizomorphic, cylindrical and hollow above, tapering below, soft orange (# edc 0 af). Basidiospores [100 / 2 / 2] (6.5 –) 7.6–9.2 × 4.6–5.8 μm, (N = 100, Q = 1.10–2.27, Q m = 1.63 ± 0.18, av. 8.43 ± 0.63 × 5.20 ± 0.47 μm, in face view limoniform with an apical papilla; in lateral view amygdaliform with a slight suprahilar depression; apical and apiculus smooth, the remaining surface verruculose to verrucose; brown-toned in 1 % Congo Red and 5 % KOH solution. Basidia 24–32 × 6–8 μm (N = 20), av. 28.6 ± 1.9 × 7.0 ± 0.4 μm, 2–4 - spored, sterigmata 3.6–7.1 μm long, narrowly clavate, or cylindrical with median constriction, flexuose, guttulate. Cheilocystidia 14–40 × 2–9 μm (N = 20), av. 26.5 ± 5.7 × 6.1 ± 1.6 μm, narowly utriform, cylindrical with median constriction, or narrowly cylindrical, flexuose, occasionally branched. Pleurocystidia not observed. Subhymenium thin-walled, 5–10 μm thick, with 2–3 layers of ovoid, fusiform or globose, and 2.3–6.8 × 1.9–5.0 μm, av. 3.4 ± 1.1 × 3.3 ± 0.8 μm. Hymenophoral trama subregular, 25–55 μm wide, consisting of thin and hyaline hyphae, narrowly cylindrical hyphal elements, 3–7 μm wide. Pileipellis two-layered: upper layer ≤ 30 μm thick, a subparallel layer of thin hyphae 1–4 μm wide; lower layer ≤ 60 μm thick, of parallel hyphae 8–12 μm wide, constricted at the septa. Stipitipellis parallel aligned, thin-walled, hyphae 3–6 µm wide, sometimes constricted at the septal. Tibiiform diverticula abundant on pseudorrhizal pellis, 10–25 × 2–4 μm (N = 14), av. 17.1 ± 3.5 × 2.6 ± 0.5 μm, flexuose, narrowly cylindrical to narrowly conical with subcapitate apex, transparent and colorless, thin-walled. Clamp connections occasionally present in pileipellis. Habitat. Solitary or scattered in broad-leaved forests. Additional specimens examined. China • Xizang Autonomous Region, Yadong County, elev. 3,130 m, 24 July 2025, Song-Ming Tang, (HKAS 154720), paratype; China • ibid., Dingjie County, Chentang Town, elev. 3,332 m, 25 July 2025, Rui-Yu Li, (HKAS 154721). Notes. Phaeocollybia dingjieensis and P. amygdalospora Bandala & E. Horak are similar in having a pileus with orange to yellowish-brown tones and a brownish stipe. However, P. amygdalospora differs by having a smaller pileus (up to 15 mm vs. 15–25 mm in P. dingjieensis), which becomes flattened with age and exhibits purplish tones, and a shorter stipe (up to 60 mm vs. 80–100 mm in P. dingjieensis). Microscopically, the basidia of P. amygdalospora are typically claviform, whereas those of P. dingjieensis often exhibit a median constriction and flexuosity. Additionally, P. amygdalospora completely lacks clamp connections in all tissues (Bandala et al. 1996), while P. dingjieensis has occasional clamp connections. These differences support the recognition of P. dingjieensis as a distinct species from P. amygdalospora. In the phylogenetic tree (Fig. 1), Phaeocollybia dingjieensis forms a sister clade to P. elegans E. Horak. However, P. elegans, with its type locality in New Zealand, differs from P. dingjieensis by having a smaller pileus (0.8–2.0 cm diam.) that is broadly conical, colored very dark orange at the center and fading to bright orange toward the margin, with a peeling pileipellis at maturity, and lacking both the light orange coloration with dark moderate orange vertical stripes and the acute central papilla characteristic of P. dingjieensis. Furthermore, P. elegans possesses a shorter stipe (4–6 cm vs. 8–10 cm) of a uniform very dark orange color. Microscopically, P. elegans produces oblong to limoniform basidiospores that are substantially smaller than those of P. dingjieensis (5 × 2.5 μm vs. averaging 8.4 × 5.2 μm); the latter species is further distinguished by verruculose to verrucose spore ornamentation, except at the apex and apiculus. The cheilocystidia of P. elegans measure 12–25 μm and are characterized by apices that are either sharply pointed (mucronate) or swollen into a spherical or subcapitate shape, whereas those of P. dingjieensis are longer (14–40 μm), narrowly utriform to cylindrical, sometimes with a median constriction, and occasionally branched. Clamp connections, occasionally observed in the pileipellis of P. dingjieensis, have not been reported for P. elegans. The ITS sequence difference between P. dingjieensis (HKAS 154723, holotype) and P. elegans (PDD 72723) was 10.03 % (56 / 558, including 11 gaps).