Rhodocybe zijinshanensis S. P. Jian & X. Chen sp. nov.

Figs 2, 3 i – k, 4 g – h, 7 a – c

Holotype.

China • Jiangsu Province, Nanjing City, Zijinshan, E 118.87, N 32.06, alt. 99 m, solitary on rotten wood, in mixed broadleaf (i. e. Quercus acutissima, Quercus aliena, Aphananthe aspera, Osmanthus fragrans, Liquidambar formosana, Photinia serratifolia and Ilex chinensis) forest, 30 August 2024, collected by X. Chen, CX 664 (KUN-HKAS 145338). GenBank: ITS = PQ 793171; LSU = PQ 781615; RPB 2 = PQ PQ 788400; TEF 1 = PQ 788406.

Etymology.

“ zijinshanensis ” indicates the source place, where it was located in Nanjing City, China.

Diagnosis.

Rhodocybe zijinshanensis is similar to R. subasyae, but differs by its smaller yellow pileus, shorter and more slender stipes and the absence of cheilocystidia.

Description.

Basidiomata omphalioid, small size. Pileus 10–15 mm wide, applanate to plano-concave; surface yellow (# eac 7 a 2) over edge and brownish-yellow (# 6 c 3620) over disc, distributing some radiate fibrillose, sometimes hygrophanous; margin slightly inflexed, even or undate; context about 1 mm thick. Lamellae adnate to subdecurrent, yellowish (# cdbead) to greyish-pink (# d 1 b 4 a 2), dense or crowded, edges entire or undate, sometimes with transverse intervenose, concolorous with lamellae, lamellulae numerous. Stipe 7–19 × 1–2 mm, central to eccentric, cylindrical to tapering downwards, usually concolorous with pileus, densely fine scales dispersed around the top. Odour none.

Basidiospores (4.5) 5–6.5 × 3.5–5 μm, L m × W m = 5.5 (± 0.54) × 4.3 (± 0.31) μm, Q = 1.09–1.55 (Q avg = 1.28 ± 0.11) [41 / 2 / 2], hyaline, subglobose, subamygdaliform to broadly ellipsoid in profile view, ellipsoid in face view and minutely, but obviously angular in polar view (7–9 facets in total), undulate-pustulate in all views. Basidia 18.5–32 × 5.5–7.5 μm, clavate, hyaline, 2 - or 4 - spored; sterigmata up to 5 μm long. Lamellar trama regular, composed of 2.5–10.5 μm in diam., thin-walled, hyaline hyphae. Lamellae edges fertile. Pleurocystidia and cheilocystidia absent. Pileipellis a cutis composed of radially arranged, subregular hyphae, hyphae thin-walled, yellowish, smooth, cylindrical, 3.5–11.5 μm in diam., sometimes with oleiferous hyphae; pileal trama regular, composed of hyaline, thin-walled, cylindrical hyphae with a diameter of 2–11 μm. Stipitipellis a cutis composed of compactly arranged, regular, thin-walled and hyaline hyphae with a diameter of 3.5–9.5 μm; Stipe trama regular, composed of thin-walled and hyaline hyphae with a diameter of 4–10.5 μm. Caulocystidia absent. Clamp connections absent.

Ecology and distribution.

Solitary on rotten wood in broad-leaved forest, only found in Jiangsu Province, China, August to October.

Additional specimens examined.

China • Jiangsu Province, Nanjing City, Zijinshan, E 118.87, N 32.06, alt. 99 m, solitary on rotten wood, in mixed broadleaf (i. e. Quercus acutissima, Quercus aliena, Aphananthe aspera, Osmanthus fragrans, Liquidambar formosana, Photinia serratifolia and Ilex chinensis) forest, 30 August 2024, collected by X. Chen, CX 665 (KUN-HKAS 145339).

Notes.

Rhodocybe zijinshanensis belongs to R. sect. Rufobrunnea (Fig. 2). Species in this section are characterised by centrally stipitate basidiomata, pilei ranged from pinkish, reddish, brown, tan to fulvous (but never greyish or white), lamellae that are adnexed to adnate or decurrent, the absence of hymenial pseudocystidia and clamp connections (Baroni 1981). Rhodocybe zijinshanensis is similar to several other species, including R. asyae Seslı & Vizzini, R. subasyae T. Bau & Y. L. Sun, R. pseudoalutacea T. J. Baroni et al. and R. alutacea Singer. Rhodocybe asyae, first recorded in Turkey, can be differentiated from R. zijinshanensis by its relatively larger, smooth pileus (10–30 mm), longer and thicker stipe (25–30 × 2–5 mm) and flexuous cheilocystidia (20–30 × 4–6 μm) (Seslİ and Vizzini 2017). Rhodocybe subasyae, a recently described species from Jilin, China, is also similar to R. zijinshanensis, but differs in having a smooth pileus, a longer and thicker stipe (22–37 × 5–7 mm), slightly larger basidiospores (Q avg = 1.4), and cheilocystidia measuring 22.4–28.2 × 3.9–6.8 μm (Sun and Bau 2023). For R. pseudoalutacea, it was reported from the Dominican Republic, featured by its slightly larger pileus (10–35 mm), slender yet thick stipe (15–50 × 2–6 mm) and pileipellis composed of finely encrusted cylindrical hyphae (Baroni et al. 2020). The last species which resembled R. zijinshanensis was R. alutacea, found in Florida, USA. It is characterised by the greater pileus size (25–35 mm), a longer stipe (23–35 × 2.5–5.5 mm), and septate, flexuous cheilocystidia (20–35 × 6.5–7 μm) (Singer 1946 b; Baroni 1981).