Agaricus endoxanthus Berk. & Broome, J. Linn. Soc., Bot.

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 : 252

Agaricus endoxanthus Berk. & Broome, J. Linn. Soc., Bot. 11(56): 548 (1871)

( Figures 2a–c , 3 )

Index Fungorum Number: 226162

Pileus 40–110 mm in diameter., broadly convex to hemispheric when young, then parabolic to plane at maturity, depressed at centre; surface dry, slightly slippery, appressed squamulose, innately scaly, greyish brown (5E1) to brownish beige (6E3), squamules easily removable on peeling; margin slightly cracked, non-striate, rimose when mature; context 4 mm thick at centre, white (1A1), fleshy, colour turns greyish yellow (1A4) on cutting, then gradually change into yellowish brown (5D 8, 5E 7) to olive brown (4E8). Lamellae free, 2–6 mm broad, close to crowded; with 2– 3 series of lamellulae, pinkish white to cream when young, becoming brown (6-7D7) to dark brown (6F6) on maturity; regular, edge even, concolorous. Stipe 30–74 × 10–12 mm, central, slightly curved, equal, surface smooth, white both above and below the annulus, dark brown (6F6-7) at the extreme base, turning yellowish brown (5D 8, 5E 7) to olive brown (4E8) on bruising; context fleshy fibrous, hollow, colour turning gradually pastel yellow (1A1) on cutting, bulbous (up to 20 mm) with white rhizomorphs. Annulus superous, double, membranous, upper surface smooth, lower surface with floccose, sometimes fibrillose scales, thick, 45 mm in diam., white (1A1). Odour indistinct.

Basidiospores [54,2,2] (5.2–)6.1–7.5(–8.2) × (3.5–)4.4–4.8(–5.3) μm, X m = 6.98 ± 0.8 × 4.56 ± 0.4 μm, Q = 1.3– 1.68, Q m = 1.53 ± 0.09, ellipsoid, smooth, brown with KOH, thick-walled. Basidia 17–21 × 5–8 μm, clavate, hyaline, gluttulate, thin-walled, smooth, 4-spored, sterigmata 1.5–3 μm long. Basidioles 13–18 × 5–6.5 μm, clavate, hyaline, thin-walled, smooth. Cheilocystidia 12–27 × 9–15 µm, pyriform to broadly clavate, sub-globose to subspherical, hyaline, thin-walled, smooth. Pleurocystidia absent. Pileipellis a cutis, hyphae 8–11 μm broad, branched, cells with brown pigments, thin-walled, smooth. Stipitipellis hyphae 5–6 μm broad, light brown with KOH, thin-walled. Annulus composed of long cylindrical hyphae, 4–10 μm broad, hyaline to light brown with KOH, not constricted at the septa, smooth, thin-walled.

Macrochemical reactions:—KOH reaction positive, pileus surface initially turning yellow (2A6, 3B6) and gradually changing to dark yellow (4C8), pileus context becoming light yellow (2A5), stipe surface at first turning olive yellow (2C8) and slowly changing to dark yellow (4C8), stipe context turning olive yellow (2C8); Schäffer reaction on pileus surface negative.

Habit and habitat:—solitary, terrestrial on humus soil under a dicotyledonous tree.

Specimen examined:— INDIA: West Bengal, Burdwan District, Burdwan University Campus , 23°15’19.5”N, 87°50’51.1”E, alt. 42.0 m asl., 17 August 2019, A.K. Dutta & K. Acharya, CUH AM755 ; Kolkata, Maidan, Race Course , 22°32’49.6”N, 88°20’05.8”E, alt. 8.0 m asl., 21 June 2021, E. Tarafder & R. Das, CUH AM765 .

Remarks: Agaricus endoxanthus was originally described from Peradeniya, Sri Lanka ( Berkeley and Broome 1871) and subsequently recorded from various countries like Uganda ( Pegler 1977), Martinique ( Pegler 1983), and Spain ( Parra et al. 2002). In India, this species was previously recorded from Kerala ( Vrinda et al. 1999; Pradeep and Vrinda 2007; Vrinda and Pradeep 2011). Our two collections constitute the first records for the state of West Bengal.

The morphological characteristics of our Indian collections match the type specimen (5.08–7.62 μm long; Berkeley and Broome 1871) as well as the material described from Uganda (4.5–6.4 × 3–4.5 μm; Pegler 1977). However, collections from Spain (4.5–6 × 3–3.8 μm; Parra 2002) and Martinique (5–6 × 3–3.5 μm; Pegler 1983) have smaller basidiospores.

Among morphologically similar taxa: Agaricus volvatulus lacks cheilocystidia and an unchanging surface ( Heinemann 1956). Agaricus sinoplacomyces P. Callac & R.L. Zhao , has a pileus surface covered with fibrillose scales breaking into small concentrically arranged squamules outside the disc, an entirely white stipe, a greater number of lamellulae (in seven series), and elongated basidiospores (Q mean 1.68; Zhou et al. 2016).

Agaricus endoxanthus is a tropical species that was first discovered in Sri Lanka ( Berkeley & Broome 1871). The morphological features of this species include the presence of dark appressed squamules on the surface of the pileus, which may exhibit a fibrillose texture or radial and/or concentric splitting. Additionally, when the stipe base is cut, a chrome yellow discoloration can be observed. The spores of this species have an average size of 6.98 × 4.56 μm. Furthermore, the pileipellis hyphae consist of elements that are clearly constricted at the septa and contain vacuolar pigment. Field features including pileus colour and yellowish discolouration when cut at the stipe base can confuse Agaricus moelleri with A. endoxanthus . However, the former has larger basidiospores (5.8 × 3.7 μm average) and filamentous pileipellis hyphae with dispersed pigment ( Kerrigan et al. 2005; Parra 2013). Agaricus endoxanthus is naturally distributed in tropical areas, but A. moelleri has only been found in non-tropical areas in Europe and Iran (Mahdizadeh et al. 2018; Parra 2013). Agaricus rotalis , first described on Hawaii Island, is now a synonym of A. endoxanthus ( Parra 2013; Kerrigan 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 3. Agaricus endoxanthus. (a) Basidiospores (b) Basidia (c) Basidioles (d) Cheilocystidia (e) Pileipellis hyphae. Scale bars: a–d = 5 μm, e = 10 μm. Drawing by: E. Tarafder