Agaricus melanocarpus R.L. Zhao

Tarafder, Entaj, Dutta, Arun Kumar, Karunarathna, Samantha C., He, Mao-Qiang, Tian, Fenghua & Acharya, Krishnendu, 2023, Agaricus sect. Xanthodermatei (Agaricales) of West Bengal, India, Phytotaxa 630 (4), pp. 245-265 : 255-256

Agaricus melanocarpus R.L. Zhao [as ‘melanocapus’], Phytotaxa 257(2): 113 (2016) ( Figures 2d–e , 4 )

Index Fungorum Number: 834198

Pileus 25–76 mm in diameter, convex with slightly central umbo when young, then broadly convex to applanate at maturity; surface moist, covered with appressed, minute, greyish brown (6-7F3) squamules, denser at the disc, scattered elsewhere, on a white background, turning pastel red (9-10A4) on bruising, margin entire, rarely rimose; context 4 mm thick at centre, white (1A1), fleshy, discolouring light yellow (1A4) on cutting. Lamellae free, 4–5 mm broad, close to crowded; with 3–4 series of lamellulae, pink when young, becoming brown (6E8-9) to dark brown (6F6-7) on maturity; regular, edge even to slightly eroded, concolorous. Stipe 60–89 × 6–13 mm, central, cylindrical, curved and tapered at apex, with a distinctly bulbous base provided with white rhizomorphs, surface slightly fibrillose at the upper half, smooth at base, white both above and below the annulus, brown (6F6) at base, white to light brown (7D5) at apex, turning brownish red (9C7) on bruising; context stuffed to hollow, white to cream, turning light brown on cutting. Annulus superous, double, membranous, upper surface smooth, lower surface with fibrillose scales, thick, 39 mm in diameter, white (1A1) to cream. Odour indistinct.

Basidiospores [52,2,2] (5.6–)5.8–6.2(–7.4) × (2.9–)3.2–3.8(–4.4) X m = 6.03 ± 0.5 × 3.6 ± 0.4 µm, Q = 1.4–2.0, Q m = 1.7 ± 0.1, ellipsoid to elongate, smooth, light brown to brown with KOH, thick-walled. Basidia 12–22 × 5–9 μm, clavate, hyaline, gluttulate, thin-walled, smooth, 4-spored, sterigmata 2–2.5 μm long. Basidioles 12–17 × 4–5 μm, clavate, hyaline, thin-walled, smooth. Cheilocystidia 12–30 × 8–12 μm, clavate to sphaeropedunculate, hyaline, thin-walled, smooth. Pleurocystidia absent. Pileipellis a cutis, hyphae 5–10 μm broad, branched, cells with dark brown vacuolar pigments, thin-walled, smooth. Stipitipellis hyphae 5–7.5 μm broad, light brown with KOH, hyaline, thin-walled. Annulus composed of long cylindrical hyphae, 5–7.5 μm broad, yellowish brown to light brown with KOH, not constricted at the septa, smooth, thin-walled.

Macrochemical reactions:—KOH reaction positive, pileus surface turning brownish yellow (5C7), pileus context becoming deep yellow (4A8) to yellowish orange (4B8), stipe surface and context turning orange (5B8) to deep orange (5A8); Schäffer reaction on pileus surface negative.

Habit and habitat:—solitary to scattered or in a small group, terrestrial on humus soil among mixed vegetation.

Specimens examined:— INDIA: West Bengal, Kalimpong District, Mongbol Busty , 27°3’47.64”N, 88°27’38.84”E, alt. 1128.0 m asl., 12 May 2018, E. Tarafder & J. Tamang, CUH AM756 ; Kamimpong District, Mongbol Busty , 27°3’47.48”N, 88°27’38.03”E, alt. 1128.0 m asl., 15 May 2018, E. Tarafder & J. Tamang, CUH AM757 .

Remarks:— Agaricus melanocarpus was originally described based on a single collection made in Yunnan Province, China ( Zhou et al. 2016). This species is identified by its small-sized basidiomata, the presence of fibrillose, minute, dark brown to black squamules on the pileus surface, and ellipsoid to elongated, small-sized (3.7–4.9 × 2.6–3.2 μm) basidiospores ( Zhou et al. 2016). Our collections differ from the type description by their larger pileus (up to 76 mm in diameter) and longer basidiospores (4.7–6.3 × 2.5–3.5 μm, X m = 5.3 × 3.1 μm) and the presence of clavate to spheropedunculate cheilocystidia (12–30 × 8–12 μm), which were not observed in the type specimen. This is the first record of this taxon outside of China.

Agaricus sinoplacomyces P. Callac & R.L. Zhao , morphologically, the closest species differs from A. melanocarpus in having yellow discolouration at the stipe surface on bruising and with KOH, and a greater number (seven series) of lamellulae ( Zhou et al. 2016).

Figures

FIGURE 2. Field photographs of the basidiomata of (a–c) Agaricus endoxanthus. (d–e) A. melanocarpus. (f) A. punjabensis. (g–h) A. xanthodermulus. Scale bars: a–c = 20 mm, d–e = 10 mm, f = 20 mm, g = 15 mm, h = 10 mm. Photographed by: E. Tarafder

FIGURE 4. Agaricus melanocarpus. (a) Basidiospores (b) Basidia (c) Basidioles (d) Cheilocystidia (e) Pileipellis hyphae. Scale bars: a–d = 5 μm, e = 10 μm. Drawing by: E. Tarafder