Gymnopus ailaoensis Y. Hu, sp. nov.

Index Fungorum number: IF 902410; Mycobank number: MB 902410; Facesoffungi number: FoF 16092; Fig. 1

Etymology – ‘‘ailaoensis’ refers to the locality “Ailao Mountains” which the species was recorded.

Holotype – HKAS 131326

Basidiocarps medium-sized, Pileus 5.3‒30.6 mm in diam, 2.2‒10.3 in height, hemispherical to slightly campanulate when young, becoming convex to plano-convex with age; margin straight to slightly reflexed, translucent striate, surface smooth, hygrophanous, light orange (6A5) to yellowish gray (6C6), margin white (1A1). Lamellae crowded, adnexed, white (1A1), margin even. Stipe 11.6‒38.6×1.9‒3.9 mm, central, cylindrical to compressed, hygrophanous, pliant, tapered toward apex, swollen to the side at base, with white basal mycelium, yellowish white (2A2) when young, light orange (6A5) to yellowish gray (6C6) with age. Basidiospores 3.5‒7.8 × 2.4‒3.9 μm, average 5.27×3.03 μm, Q =1.4‒2.6 (mean=1.75), ellipsoid to oblong to lacrymoid, smooth, thin-walled, with drops. Basidia not seen, Basidioles narrowly clavate, curved. Pileocystidia 34.2‒103.5 × 3.6‒8.8 μm, cylindrical, curved, slightly swollen toward apex. Cheilocystidia 17.7‒27.8 × 3.1‒5.6 μm, subcylindrical to narrowly utriform, tapered toward apex. Caulocystidia 27.0‒57.9 × 3.7‒8.2 μm, narrowly cylindrical, irregular. Pileipellis hyphae 3.3‒7.2 μm wide, thin-walled, intricate trichoderm. Stipitipellis hyphae 4.9‒8.1 μm, cutis, thickwalled. Clamp connection present in all tissues. Odour and taste not recorded.

Materials examined – CHINA, Puer, Jingdong, Ailao Mountains, 24° 32′ 45″ N, 101° 01′ 48″ E, alt. 2,503 m, 8 June 2021, Yuwei Hu, ALS33 (HKAS 131326, holotype).

Other materials examined – CHINA, Puer, Jingdong, Ailao Mountains, 24° 32′ 35″ N, 101° 01′ 39″ E, alt. 2,491 m, 8 June 2021, Peter E. Mortimer, ALS70 (HKAS 131325, paratype); Puer, Jingdong, Ailao Mountains, 24° 32′ 19″ N, 101° 01′ 07″ E, alt. 2,483 m, 8 June 2021, Peter E. Mortimer, ALS71 (HKAS 131324, paratype).

Habitat – Gregarious on dead wood.

GenBank numbers – ITS: OR815363 (HKAS 131326), OR815364 (HKAS 131325), OR815365 (HKAS 131324); nrLSU: OR815381 (HKAS 131326), OR815382 (HKAS 131325), OR815383 (HKAS131325).

Notes – Phylogenetically, Gymnopus ailaoensis belongs to Gymnopus sect. Levipedes and forms a sister lineage with G. earleae and G. bicolor. Gymnopus ailaoensis is similar to Gymnopus earleae by basidiocarp size (cap 0.5‒2 cm vs. 1‒3.5 cm; stipe 11.6‒38.6×1.9‒3.9 vs. 20–50×5 mm) and basidiospore size (3.5‒7.8×2.4‒3.9 vs. 4.5‒7×2‒3.5). However, Gymnopus ailaoensis is distinct by orange to yellowish gray pileus and stipe while Gymnopus earleae presents dark brown to dark reddish-brown cap (Murrill 1916). Gymnopus ailaoensis is morphological similar to G. bicolor, while G. ailaoensis has an entire subcylindrical to narrowly utriform cheilocystidia (17.7‒27.8×3.1‒5.6 μm,) and G. bicolor has a broadly clavate and lobulate cheilocystidia (17.5‒25.5×6.5‒9.5 μm) (Wilson et al. 2004).

Figure 1 – Gymnopus ailaoensis (HKAS 131326, holotype). a, basidiocarps on dead wood, b, basidiocarps in laboratory, c–e, basidiospores, f, basidioles, g, Pileocystidia, h cheilocystidia, i, caulocystidia. Scale bar: b=5 cm, c–e=5 μm, f–i=20 μm