Agaricus shenzhenensis P. H. Liu & S. E. Wang, 2025

Wang, Shi-en, Chen, Si-ang, Huang, Hai-chen, Lin, Dong-mei & Liu, Peng-hu, 2025, Three new species of Agaricus (Agaricaceae, Agaricales) from southern China, MycoKeys 119, pp. 47-66 : 47-66

Agaricus shenzhenensis P. H. Liu & S. E. Wang sp. nov.

Figs 2 E, F , 5

Etymology.

shenzhenensis (Latin), meaning from shenzhen city where the holotype specimen was collected.

Holotypus.

China • Guangdong Province, Shenzhen City, Lianhuashan Park , 29 April 2024, 22°33'23"N, 114°3'13"E, alt. 100 m, Cheng-Cheng, 20240430 ( FFAAS 3397 ) .

Diagnosis.

Distinguished by the pileus adorned with brownish gray (6 E 2) fibrillose squamules, context becoming yellow (3 B 8) on cutting, stipe base tapering and covered with brownish gray (6 E 2) fibrillose squamules, predominantly 2 - spored basidia.

Description.

Pileus 2.5–6.5 cm in diameter, 0.5–0.8 cm thick at the center, hemispherical, truncate conical to plane, applanate with a slightly depressed center when mature, surface dry, white (2 A 1), grayish white (2 B 1), entirely covered with appressed, concentrically arranged, triangular, brownish gray (6 E 2) fibrillose squamules, scattered towards the margin in age, denser taupe (4 F 1), black (2 F 1) at the disc, margin entire, appendiculate by annulus remnants. Context of the pileus white (6 A 1), becoming yellow (3 B 8) on cutting, odor unknown. Lamellae 0.5–0.7 cm broad, first pale red (9 A 3) then reddish brown (8 E 8), later brownish black (8 F 8), free, crowded, intercalated with numerous lamellulae. Stipe 4.5–11.5 × 0.5–2.0 cm, cylindrical, tapering downwards, hollow, with short white (6 A 1) rhizomorphs, provided with an annulus in its upper part, above the annulus white (6 A 1), below the annulus the upper half white and the lower half covered with dense adpressed brownish grey (6 E 2) squamules concolorous with the pileus surface. Annulus superior, white (6 A 1) to brownish black (8 F 8), simple, membranous, persistent.

Basidiospores (5.8) 6.1–7.3 (7.5) × (3.8) 4.0–4.3 (4.4) μm, [Xav = 6.8 × 4.2 μm], Q = 1.41–1.87, Qav = 1.61, ellipsoid to elongate-ellipsoid, smooth, brown, thick-walled, guttulate. Basidia 25–33 × 8–10 μm, clavate, 2 (4) - spored, sterigmata 2–3 µm long. Cheilocystidia abundant, broadly clavate, oblong or pyriform, 22–50 × 10–22 μm. Pleurocystidia absent. Pileipellis a cutis of cylindrical, slightly constricted at the septa, light brown hyphae, 4–7 μm wide.

Habitat and distribution.

Gregarious or clustered in grass or broad-leaved forests during spring. Currently, it is only known from Guangdong Province, China.

Additional specimens measured.

China • Guangdong Province, Shenzhen City, Lianhuashan Park , 29 April 2024, Cheng-Cheng, 20240430-1 ( FFAAS 3398 ) .

Notes.

Agaricus shenzhenensis belongs to A. (subg. Pseudochitonia ) sect. Catenulati, which currently comprises three species: A. arabiensis S. Hussain & Al-Sadi , A. lannaensis N. Suwannarach, J. Kumla & S. Lumyong and A. malakandensis .

Agaricus shenzhenensis differs from all three in both morphological and molecular characters. Agaricus arabiensis exhibits a reddish-brown to dark reddish-brown pileus, context unchanged on handling, smooth stipe, and globose to subglobose or broadly clavate, regularly catenulate cheilocystidia ( Hussain et al. 2022). Agaricus lannaensis differs in having brown pileus, reddish brown context when cut, fibrillose stipe white below the annulus to the base, and smaller basidia (19–26 × 5.5–8.5 µm) ( Jaichaliaw et al. 2021). Agaricus malakandensis possesses a dark brown to reddish brown pileus, smooth or fibrillose to slightly squamulose stipe, and multiseptate cheilocystidia with clavate to pyriform terminal element ( Nawaz et al. 2024). Notably, catenulate cheilocystidia were not observed in this species, even though this feature is the primary morphological diagnostic characteristic for taxa within this section.

The genetic distinctions between A. shenzhenensis and A. malakandensis remain unequivocal, with four nucleotide differences in the ITS region, one in nrLSU, and four in tef 1 - α (Table 2 ). To ensure the accuracy of the results, we rechecked the quality of the sequences and confirmed their compliance with the required standards.

Notably, this species represents the first record of A. sect. Catenulati in China, expanding the known biogeographic range of this section.

Figures

Figure 2. The photographs of fresh basidiomata of Agaricus species in this study. A. A. aurantifibrillosus (FFAAS 3390); B. A. aurantifibrillosus (FFAAS 3391); C. A. fafuinus (FFAAS 3393); D. A. fafuinus (FFAAS 3394); E. A. shenzhenensis (FFAAS 3397); F. A. shenzhenensis (FFAAS 3398). Scale bars: 1 cm.

Figure 5. Agaricus shenzhenensis (FFAAS 3397, FFAAS 3398); A. Basidiomata; B. Basidiospores; C. Basidia; D. Cheilocystidia; E. Pileipellis. Scale bar: 1 cm (A); 5 μm (B – E).