Hypholoma darjeelingense J. Tamang & Acharya [as ‘darjeelingensis’], in Cao et al., Fungal Diversity 132, 563 (2025)

Fungal Names: FN 571926; Index Fungorum number: IF 571120; Mycobank number: MB 571120;
Etymology – The species epithet refers to the type locality.
Holotype – CUH AM904.

Pileus 5–15 mm in diameter, convex to broadly convex with age, surface smooth, dry, surface uniformly orange (6A6) in colour; margin non-striate, incurved bearing dense white velar remnants. Pileus context thin <1 mm. Lamellae adnexed to sinuate, close to sub-distant, regular, brownish orange (5C3) with lamellulae of 3–4 tier; lamellae edges slightly wavy.  Stipe 25×2 mm, orange white (5A2) to pale orange (5A3) in colour, hollow, cylindric, equal, slightly fibrillose with a white mycelial pad at the base. Partial veil, a fragile fringe of fibrils forming an annular zone at the stipe upper region in both immature and mature stages.

Basidiospores (5.6–)6.84–7.5–8.2 × 3.9–4.7–5.13 μm, Q=1.25–1.66, Qm=1.60, ellipsoid to elongate, yellowish brown, smooth and thick-walled, turn yellowish with KOH, apically truncated by a broad germ pore. Basidia 15.7– 20.8 × 5.7–6.6 μm, clavate, hyaline, 4-spored. Pleurocystidia present as abundant chrysocystidia, 22.8–31.35 × 7.6–10.83 μm, smooth, thin-walled, with amorphous yellowish contents, fusoid to clavate with mucronate apex. Lamellae edge heteromorphous; cheilocystidia 21.37–25.65× 5.98–8.5 μm, abundant in clusters, hyaline, subcylindrical to lageniform, subcapitate and thin-walled. Pileipellis cutis of parallel, hyaline, thin-walled hyphae, 2.2–5.7 μm wide. Hymenophoral trama regular, hyaline or yellow of thin-walled hyphae, 2–6 μm in diameter, inflated to 10.2 μm diameter. Clamp connections present in most hyphae.

Material examined – INDIA, West Bengal, Darjeeling District, Love Road, 27°03′41′′N 88°15′13′′E, elevation 1999 m, 21 June 2019, J. Tamang & A. Thapa, ALI-240/2019 (CUH AM952, holotype); ibid., 17 July 2022, J. Tamang, F–59/2022 (CUH AM951).

Habit and habitat – Caespitose, growing in clusters on decaying stumps.

GenBank data – CUH AM952: PP474310 (ITS); CUH AM951: PP474299(ITS).

Notes – Hypholoma darjeelingensis is characterized by its small-sized, brightly coloured basidiomata, non-striate margin covered with dense white velar remnants; the presence of a fibrillose partial veil forming an annular zone in stipe in both immature and mature basidiomata; and basidiospores ellipsoid to elongate with a broad germ pore.

Morphologically, Hypholoma darjeelingensis is similar to H. australe (Murrill) Murrill, but it differs in having larger basidiomata (15–45 mm broad) along with the absence of partial veil remnants in the stipe at mature stages (Miller and Pearce 1996). The collected specimen also shows morphological similarity with H. subviride (Berk. & M.A. Curtis) Dennis but differs in having a flattened pileus surface at a mature stage, a slightly smaller stipe (6–16 mm), and the partial veil covering the gills in the early stage and absent in mature basidiomata (Cortez and Silveira 2007). Phylogenetic and Blastn analyses reveal that H. darjeelingensis is closely related to H. frowardii (Speg.) Garrido, H. australe, H. brunneum (Massee) D.A. Reid, and undescribed species of Hypholoma sp. reported from Vietnam. Hypholoma sp. from Vietnam, which is forming a sister clade with our specimen H. darjeelingensis, has no published data, so morpho-anatomical comparison is not possible. However, H. australe differs in having larger basidiomata (15–45 mm broad) and larger-sized pleurocystidia (31–46 μm), along with the absence of partial veil remnants in the stipe at mature stages (Miller and Pearce 1996); H. brunneum from New Zealand differs in having large-sized (40–50 mm broad) dark olive brown to nearly black basidiomata (Horak 1971).

Fig. 1. Hypholoma darjeelingensis (holotype). A-B Basidiomata in the field. C Close up of lamellae. D Basidiospores. E, F Basidium. G, H Chrysocystidia. I-K Cheilocystidia. Scale bars: A-C=10 mm, D-K=10 μm.