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

Parra, Luis A., Angelini, Claudio, Ortiz-Santana, Beatriz, Mata, Gerardo, Billette, Christophe, Rojo, Carlos, Chen, Jie & Callac, Philippe, 2018, The genus Agaricus in the Caribbean. Nine new taxa mostly based on collections from the Dominican Republic, Phytotaxa 345 (3), pp. 219-271 : 260-262

Agaricus endoxanthus Berk. & Broome, J. Linn. Soc., Bot. 11: 548. 1871. ( Fig. 19 )

= Agaricus rotalis K.R. Peterson, Desjardin & Hemmes, Sydowia 52(2): 244. 2000.

Macroscopic description: Pileus (2–) 3.5–4 cm diam., hemispherical then plane, at first uniformly covered by gray appressed fibrils with an entire blackish brown center, then tending to crack radially and concentrically forming small quadrangular scales over the white background of context. Surface smooth or fissurate, dull and dry. Margin thin, slightly exceeding the lamellae. Lamellae free, crowded, slightly ventricose, intercalated with numerous lamellulae, at first whitish rose, then dark brown, finally dark brown with the edge concolorous and slightly eroded. Stipe 3–6 × 0.3–0.5 cm, cylindrical, curved at base, sometimes sinuate, fistulose, with an annulus in the upper third, above annulus white and smooth, below annulus white, grayish towards the base, at maturity completely grayish brown, except the base in contact with the substrate, which is covered with white cottony mycelium, smooth or slightly fibrillose towards the base. Annulus superous, double, white, up to 1.2 cm broad, with thick margin and thin at insertion, upper surface white and smooth, lower surface white with squamules arched dispersed in the perimarginal area, concolorous with pileus. Context somewhat dense, when cut at first white, then chrome yellow at the stipe base, with a strong odor of phenol.

Microscopic description: Spores 4.34–4.77–5.17 × 2.90–3.05–3.10(–3.31) μm, Q=1.40–1.57–1.72, ellipsoid, smooth, brown, without apical pore. Alongside these mature dark brown spores there are also abundant hyaline spores among which are frequently giant spores of 6.00–6.33–7.11 × 3.1–3.4–3.6 μm, Q=1.71–1.87–2.00, ellipsoid-elongated sometimes with a constriction in the middle. Basidia 13–15 × 5.5–6.5 μm, tetrasporic, clavate or slightly truncate at the apex, sterigmata up to 3 μm long. Cheilocystidia abundant, hyaline, generally simple, clavate, pyriform or spherical more or less sphaeropedunculate, 9–15(–20) × 6–13 μm. Pleurocystidia not observed. Lower surface of the annulus hyphae hyaline or with pale brown diffuse pigment, cylindrical or narrowed at the septa, 3–6(–8) μm wide. Inflated elements not observed. Pileipellis a cutis with transition to a trichoderm, composed of hyphae with the internal elements hyaline and the external ones completely dark brown because of the presence of diffuse pigment, or hyaline with one or two large vacuoles of dark brown pigment. The hyphal elements can be cylindrical, slightly narrowed at the septa or 4–9 μm wide, or very narrow at the septa, doliiform, globose-ovoid of 8–20 μm wide. Clamp connections not observed.

Macrochemical reactions: Schäffer’s reaction negative. KOH reaction positive, color pale yellow.

Habit, habitat, occurrence and distribution: Gregarious in groups of few basidiomata, in lowland broadleaf forests. Very rare. Cosmopolitan. In the Caribbean region, this species has been recorded in the Dominican Republic and Puerto Rico ( Parra 2013).

Note: This species is characterized by its small to medium size, the gray-tinted pileus with the always-darker center, blackish, soon cracking radially and/or concentrically, the stipe base grayish, the context at the stipe base turning chrome yellow, the odor of phenol and the outermost elements of the pileipellis doliiform, ovoid or globose containing large vacuoles of dark brown pigment.

Material examined: DOMINICAN REPUBLIC, Distrito Nacional, Santo Domingo de Guzmán, at the park in the Jardín Botánico de Santo Domingo, 24 November 2014, JBSD 126486 ( LAPAM 47).

Taxonomic comments: Species originally described from Sri Lanka, with a wide distribution in tropical Africa, Asia, the Caribbean, Oceania and South America, as well as in greenhouses and indoor gardens with tropical vegetation in Europe and USA ( Parra 2013; Chen et al. 2016b).

The presence of hyaline macrospores in this species seems to be frequent, having also been mentioned by Guzmán (1983) in collections from the Yucatan Peninsula ( Mexico) and Parra (2013) from a French collection ( LAPAG 597) made in an indoor tropical garden.

Its synonymy with A. rotalis proposed by Parra (2013), based on the study of the types of both species and numerous collections from around the world, has been confirmed by a recent study on inter- and intraspecific variability of A. endoxanthus and closely related species ( Chen et al. 2016b). From a morphological point of view, the most similar species to A. endoxanthus are A. moelleri Wasser (1976: 77) , A. moelleroides Guinb. & L.A. Parra (2013: 109) , A. punjabensis T. Qasim, A. Ashraf & A.N. Khalid ( Chen et al. 2016b: 8) and A. volvatulus Heinem. & Gooss. -Font. (1956: 61), but the first three lack the large vacuoles in the pileipellis elements and have not been found so far neither in tropical areas nor in indoor habitats with tropical vegetation ( Chen et al. 2016b; Mahdizadeh et al. 2016; Parra 2013) and A. volvatulus , that also has large vacuoles in the pileipellis, lacks cheilocystidia and its stipe is white to the base, which is usually marginately bulbous ( Heinemann 1956; Chen et al. 2016b).

Additional comments: A phylogenetic study of this species, including this collection, has been recently published by Chen et al. (2016b).

Figures

FIGURE 19. Macroscopic characters of A. endoxanthus. A–C. Basidiomata (JBSD126486). Microscopic characters of A. endoxanthus. D–J. In ammoniacal Congo red. (JBSD126486). D–E. Cheilocystidia. F. Basidia. G. Spores. H. Hyphae of the lower surface of the annulus. I–J. Pileipellis hyphae. Photos by C. Angelini (A–C) and L.A. Parra (E–J).