Gerronema brunneosquamulosum Q. Na & Y. P. Ge

Gerronema brunneosquamulosum Q. Na & Y. P. Ge , MycoKeys 105: 49 ( 2024-04-25)

Figs 3 View Figure 3 , 5 View Figure 5 , 7 D Chinese name: 雷丸老伞 View Figure 7

Synonym.

Gerronema lapidescens (Horan.) Ming Zhang & W. X. Zhang , Acta Edulis Fungi 31: 90 ( 2024-06-15), syn. nov.

Remark.

The following description draws mainly from Na et al. (2024) and Zhang et al. (2024 b), supplemented by our field observations and covers macro-morphology, growth habit, geographical distribution and micromorphological characteristics.

Description.

Basidiomata small to medium-sized, with a flexible texture. Pileus 2–6 cm diam., cup- or funnel-shaped, slightly depressed at centre when young, gradually becoming funnel-shaped with growth; initially dark brown (4 F 5–4 F 6), becoming progressively lighter with development, transitioning to dark grey-brown (4 E 5–4 E 6) and pale grey-brown (2 C 2) towards the margin; edge paler, greyish-white (2 B 2), with radial striations or small squamules; surface dry. Context thin, fragile, yellowish-white (1 A 2). Lamellae decurrent, creamy-white, with the same colour on both surfaces and edges, 30–40 pieces of complete lamellae per pileus. Stipe 1.5–4.5 × 0.1–0.4 cm, central, cylindrical, hollow; surface initially pale white (1 A 1), developing sparse grey (1 B 1) scales with age, predominantly scattered along entire stipe; base turning yellow-brown (1 B 4) at maturity, slightly swollen. Odour and taste indistinct. The cultured mycelium of G. brunneosquamulosum grows prostrately on the surface of the medium, exhibiting a concentric zonation pattern with radially extending hyphae. The colony margin is smooth and well-defined.

Basidiospores [40 / 2 / 2] 6.0–8.0 (9.0) × 4.0–5.0 μm (Q = 1.4–2.0, Q m = 1.63 ± 0.2), inamyloid, ellipsoid to elongate-ellipsoid. Basidia 25–40 × 6–9 μm, clavate, 4 - spored, occasionally 2 - spored; sterigmata up to 5 μm long. Cheilocystidia clavate, 18–35 × 4–6 μm and thin-walled. Pleurocystidia absent. Lamellar trama subregular; hyphae 2–12.5 μm wide, thin-walled and hyaline. Pileipellis a cutis; hyphae 2–7 μm wide, light yellow to yellow (1 A 6–1 B 6); terminal elements 25–75 × 8–15 μm, clavate, sometimes with sparse coarse excrescences and light yellowish-brown to yellowish-brown (1 A 5–1 B 5) pigment in KOH. Pileus trama subregular, sarcodimitic, sometimes containing dark brown (1 C 4–1 C 5) hyphae. Stipitipellis composed of hyphae 2–10 μm wide, hyaline, smooth. Caulocystidia 27–55 × 6–12 μm, clavate, thin-walled; light yellowish-brown (2 A 7–2 A 5) pigment in KOH. Clamp connections present in all tissues.

Sclerotia 0.8–3.5 cm diam., elliptical to irregularly globose; peridium thin, brown (2 D 8–2 E 8), fissured when fresh, drying dark brown (2 E 7–2 F 7) to black, fissures deepened, texture slightly wrinkled. Internal structure dense, firm, hard, often exhibiting white marble-like veins; cut surface showing intertwined wax-yellow (2 A 2) and milky-white (1 A 1) striations; comprising irregularly shaped translucent compartments, 1–2 mm wide, separated by white septa; compartments near the outer layer of the sclerotium are typically smaller. Odour indistinct. Rhizomorphs brown (2 D 8) to dark brown (2 E 7), arising from sclerotia, with vessel hyphae facilitating long-distance translocation of water and nutrients, caducous upon drying. Sclerotial context primarily composed of compact thick-walled hyphae and viscous substances, hyphae 2–6 μm wide, thick-walled, 1 μm thick, hyaline. Clamp connections present, rare. Sclerotial rind with yellowish-brown (2 B 5–2 C 5) pigment in KOH.

Habit and habitat.

Gregarious on decayed wood in broad-leaved forests dominated by Cyclobalanopsis glauca (Thunb.) Oerst. and Castanopsis eyrei (Champ.) Tutch. ( Fagaceae ) or at the bases of bamboo.

Distribution.

Known to be primarily in the regions southern of the Yangtze River in China: Anhui, Chongqing, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Sichuan, Yunnan and Zhejiang.

Materials examined.

China: Anhui Province: Shitai Prefecture (石台县), Xianyu Town (仙寓镇), Yuantou Village (源头村), 30°3'42"N, 117°17'23"E, elev. 204 m, 1 July 2022, Lin-Jie Su ( MHKMU SLJ-213 ) GoogleMaps ; Shitai Prefecture (石台县), Qidu Town (七都镇), Huanghe Village (黄河村), 30°12'22"N, 117°49'52"E, elev. 284 m, 2 August 2022, Qin Deng ( MHKMU DQ-063 ) GoogleMaps . Chongqing Province: Nanchuan District (南川区), elev. about 800 m, 8 August 2019, CQNC ; Nanchuan District, elev. about 800 m, 2 August 2020, LWBZ ; Wulong District (武隆区), elev. about 1,000 m, 2 August 2018, CQWL . Guangxi Province: Duan County (都安县) Longwan Town (龙湾乡), elev. about 400 m, 8 March 2022, Wen-Hao Zhang ( MHKMU ZWH-839 -1) . Guizhou Province: 8 March 2022, Wen-Hao Zhang ( MHKMU ZWH-838 ) ; Daozhen Prefecture (道真县), elev. 2 August 2020, GZDZ . Hainan Province: 22°51'35"N, 101°1'57"E, elev. 1878 m, 18 September 2020, Cai-Rui Fu ( MHKMU FCR-001 ) GoogleMaps . Sichuan Province: 5 April 2022, Wen-Hao Zhang ( MHKMU WH Zhang 840) ; Hejiang Prefecture (合江县) elev. 300-500 m, 11 October 2019, SCHJI and SCHJII . Yunnan Province: Lancang Lahu Autonomous County (澜沧拉祜族自治县), 21 July 2021, Li-Ping Tang ( MHKMU TLP-3572 ) and Li-Ping Tang ( MHKMU TLP-3573 ) .

Notes.

Gerronema brunneosquamulosum was originally described by Na et al. (2024) from Zhejiang Province, China and is characterised by a brownish pileus with radial striations and small squamules, elongate basidiospores (Q m = 1.73) and the presence of clamp connections across all tissues. Notably, the original description did not document sclerotial formation. In contrast, G. lapidescens was described by Zhang et al. (2024 b) from Guangdong Province following isolation from Leiwan sclerotia, with detailed morphological descriptions of the sclerotia provided. In our study, we present a more comprehensive morphological characterisation and demonstrate that all diagnostic features of G. brunneosquamulosum align with those of G. lapidescens .

Furthermore, phylogenetic analyses, based on ITS and nrLSU sequences, reveal that G. brunneosquamulosum and G. lapidescens form a highly supported monophyletic clade (see Fig. 1 View Figure 1 ), with negligible genetic divergence — exhibiting only 0–2 bp differences across both the ITS (600 bp) and nrLSU (800 bp) regions. Based on this integrated re-evaluation of morphological and phylogenetic evidence, we conclude that G. lapidescens and G. brunneosquamulosum are conspecific. In accordance with Article 11 of the International Code of Nomenclature for Algae, Fungi and Plants (ICN; Melbourne Code; McNeill et al. (2012)), which stipulates nomenclatural priority for the earliest validly published name amongst competing synonyms at the species rank, G. brunneosquamulosum is hereby recognised as the correct name and G. lapidescens is treated as its later synonym. This study supplements the original description by providing comprehensive morphological data for G. lapidescens (= G. brunneosquamulosum ) across all developmental stages, integrating field observations with findings from artificial cultivation.

Gerronema brunneosquamulosum is morphologically similar to G. zhujian Q. Na, H. Zeng & Y. P. Ge , as both species possess pilei with radial striations or minute scales. However, G. zhujian can be distinguished by its smaller basidiomata ( 0.8–1.8 cm in diameter) and narrower basidiospores (6.7–8.0 × 3.7–4.6 μm).

The comparisons between G. brunneosquamulosum and the newly-proposed G. sinense are given in the notes for the latter species.