Agaricus caribaeus Pegler, Kew Bull. Addit. Ser.

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 : 258-260

Agaricus caribaeus Pegler, Kew Bull. Addit. Ser. 6: 436. 1983. ( Fig. 18 )

Macroscopic description: Pileus 2–3 cm diam., hemispherical, soon plano-convex, sometimes slightly depressed at center or umbonate, densely covered by gray appressed squamules on a whitish background with an entire almost black center. Surface dull and dry. Margin white, thick, with cottony remnants from the partial veil in young basidiomata, slightly exceeding the lamellae and fimbriate, sometimes cracked. Developing a slightly pinkish tint on handling. Lamellae free, moderately crowded, straight, intercalated with numerous lamellulae, at first off-white, then pink, finally dark brown with the edge paler and eroded. Stipe 3–5(–8) × 0.3–0.4 cm, cylindrical, curved at base, with an annulus in its upper third, above annulus smooth, at first white, then light pink and finally pale gray, below annulus white, smooth, sometimes at base (where is covered by plant remains) fibrillose-lanose. Not or slightly yellowing when handled. Annulus superous, double, white, up to 0.2 cm broad, persistent, thick and adpressed to stipe, with the upper surface and the margin of the lower surface cottony, the surface closer to the stipe smooth, forming a white to slightly grayish bracelet adpressed to the stipe. Context when cut white or slightly yellowing at the base, with fungoid odor.

Microscopic description: Spores (4–)4.33–4.82–5.25(–5.67) × 2.8–3.2–3.6 μm, Q=1.32–1.52–1.72, ellipsoid, smooth, brown, without apical pore. Basidia 10–18.5 × 6.5–8.5 μm, tetrasporic, clavate or slightly truncated at the apex, sterigmata up to 3 μm long. Cheilocystidia absent in JBSD123820, rare and difficult to observe, isolated or in small fascicles of 3 to 7 cheilocystidia in JBSD126485, hyaline, simple, rarely with a basal septum, cylindrical, clavate, fusiform or enlarged at apex with lateral excrescences, 15–30 × 5–9(–12) μm. Pleurocystidia not observed. Lower surface of annulus composed of cylindrical hyphae, not or slightly narrowed at the septa, 2–4 μm wide. Inflated elements not observed. Pileipellis a cutis, with transition to a trichoderm at the squamulose disc. At the disc composed of hyphae with versiform basal elements, more or less polyhedral from which two types of dark brown, almost black elements arise, some cylindrical and thin, slightly narrowed at septa with rounded apex of 3–6 μm wide, and others doliiform, narrower at septa of 6–11 μm wide, the pigment is diffuse or in vacuoles, and terminal elements are obpyriform. The rest of the pileus is composed of hyphae of two types, some consisting of thin, cylindrical elements, slightly narrowed at septa with diffuse pigment and rarely with small vacuoles similar to these of the disc, and others thicker, hyaline, the wider the more constricted at septa, of 5–10 μm wide. Clamp connections not observed.

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

Habit, habitat, occurrence and distribution: Gregarious, in lowland broadleaf forests. Rare. Recorded only from the Dominican Republic and Martinique. Pegler (1983) designated the holotype (Fiard 442B) from a collection collected by J.-P. Fiard in Martinique.

Note: This species is characterized by its small size, the pileus covered by grayish appressed squamules with the center darker almost black, the stipe typically long and thin, the double annulus, somewhat ample, thick, adpressed to stipe, cottony on the lower surface forming a narrow bracelet smooth and adpressed to stipe, by the fungoid odor and context and surfaces not or very weakly yellowing on handling.

Material examined: DOMINICAN REPUBLIC, Puerto Plata, Sosúa, Puerto Chiquito , 20 November 2011, JBSD123820 ( LAPAM19 ) ; Puerto Plata, Sosúa, Puerto Chiquito , 29 November 2013, JBSD126485 ( LAPAM41 ) .

Taxonomic comments: Our determination of collections JBSD 123820 and JBSD 126485 as A. caribaeus is based on the fact that their ITS 1+2 sequences are identical to those of a collection (F2530), deposited in GenBank (JF727856), made by J.-P. Fiard (collector of the holotype) on the island of Martinique in the “bois de la Pointe Rouge”, where the holotype was also collected.

Although the collections of A. caribaeus from the Dominican Republic studied here agree very well with the original description, figures and photograph of Pegler (1983), there are several divergent characters discussed below. Pegler (1983) indicated that the margin of the pileus is “slightly plicate to sulcate” and the “Schäffer’s reaction positive” whereas our two collections had a smooth margin that exceeded the lamellae and was fimbriate, and the Schäffer’s reaction was clearly negative. Since Pegler (1983) indicated that the margin of the pileus lacked scales, it is very possible that the only specimen (holotype) on which his description is based was collected after heavy rain, which could explain the plicate or sulcate margin lacking scales, due to the scanty context in the pileus of this species. As for the positive Schäffer’s reaction it could be due to a misreading of the test, which is not uncommon in the species of A. sect. Xanthodermatei , since the aniline alone usually colors the pileus of the species of A. sect. Xanthodermatei orange. We must also take into account that the phylogenetic analyses show that A. caribaeus belongs to A. sect. Xanthodermatei within which no species with positive Schäffer’s reactions are currently known.

Microscopically, spores of the Dominican collections are somewhat longer ([4.00–]4.33–4.82–5.25[–5.67] × 2.8– 3.2–3.6 μm) than those indicated by Pegler for the holotype (5.0–5.5–6.0 × 2.5–3.2–3.5 μm) although values overlap to some degree, so, given the low number of collections that we have of this taxon, they could perfectly be within its intraspecific variability.

The most divergent characters between the holotype described by Pegler (1983) and the Dominican collections are the shape and abundance of cheilocystidia since this author describes the “lamellae edge sterile, with crowded cheilocystidia” which are “pyriform”, and the Dominican collections either lack cheilocystidia ( JBSD 123820) or these are very few and isolated in small groups and versiform ( JBSD 126485) but not pyriform. However, in Fiard’s personal notes of F2530, he included a microscopic drawing showing that cheilocystidia are broadly clavate to pyriform, and he indicated that they were rare. In other species of Agaricus we have already observed this type of versiform cheilocystidia in some collections, while others had sphaeropedunculate cheilocystidia or lacked them as in A. pseudolutosus . In A. sect. Xanthodermatei , A. laskibarii also has collections with versiform cystidia very similar to those observed in the Dominican collections of A. caribaeus and other collections with clavate or pyriform cheilocystidia ( Parra 2013).

For all the above, and despite the divergent elements between the original description, on a single collection by Pegler (1983) and the two Dominican collections, we consider our collections within the Agaricus caribaeus concept.

Figures

FIGURE 18. Macroscopic characters of A. caribaeus. A–B. Basidiomata. A. (JBSD123820); B. (JBSD126485). Microscopic characters of A. caribaeus. C–M. In ammoniacal Congo red. C–D, G–H. (JBSD123820); E–F, I–M. (JBSD126485). C–F. Cheilocystidia. G–H. Basidia. I. Spores. J. Hyphae of the lower surface of the annulus (a terminal hypha is marked with an asterisk). K–M. Pileipellis hyphae (K–L. pigmented terminal elements at disc). Photos by C. Angelini (A–C) and L.A. Parra (D–M).