Agaricus tephrolepidus L.A. Parra, C. Billette, Angelini, G. Mata & Callac, 2018

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 : 264-266

Agaricus tephrolepidus L.A. Parra, C. Billette, Angelini, G. Mata & Callac , sp. nov. ( Fig. 21 )

MycoBank: MB823284.

Etymology: for the very dark color (in Greek “ tephros ”) of the pileus scales (in Greek “ lepidos ”).

Original description, Macroscopic description: Pileus (3–)4–5(–6) cm (Dominican collection) or 6.5–8.4 cm (Mexican collection) diam., at first globose, then convex and finally applanate with broadly umbonate disc, at first covered with grayish-brown to brown fibrils slightly separated from each other, later becoming squamose, dense at the disc and more scattered towards the margin, on a pale mouse gray background with age, discoloring brown-red especially at the margin with high humidity. Surface smooth, dull and dry. Margin incurved when young then straight not exceeding the lamellae. Lamellae free, crowded, at first light pink, dark brown to dark grey with age. Stipe 5–6.5 × 0.5–0.7 cm (0.8–1.2 cm at the base) for the Dominican collection, 8 × 0.9–1.3 cm for Mexican collection, generally curved in the lower half, clavate to bulbous at the base which has small rhizomorphs, smooth and white above and below annulus, becoming slowly reddish brown on handling. Annulus superous, double, white, up to 0.5 cm broad, at first thick and adpressed to the stipe, later in mature basidiomata horizontal or pendant, narrow, upper surface slightly striate, lower surface initially with a fibrillose margin and a smooth surface near the insertion separated by a rim, later this rim fractures radially into broad radial scales resembling a cogwheel. Context initially white when cut, changing slowly to reddish brown with time. Odor not reported in the Dominican collection, pleasant fungoid in the Mexican collection.

Microscopic description: Spores (for the Dominican collection) 4.37–4.90–5.33 × 3.20–3.60–3.94 μm, Q=1.17– 1.36–1.50, ellipsoid, smooth, brown, without apical pore. For the Mexican collection see note below. Basidia 11–16 × 6.0–7.5 μm, tetrasporic, clavate or slightly truncated at the apex, sterigmata up to 3 μm long. Cheilocystidia (for the Dominican collection) 8.0–22.5(–28.0) × 6.0–12.5 μm, abundant, hyaline and smooth, clavate, broadly clavate, pyriform or globose more or less sphaeropedunculate. For the Mexican collection see note below. Pleurocystidia not observed. Lower surface of the annulus composed of hyaline hyphae, cylindrical, not or slightly narrowed at the septa, 3–7 μm wide. Inflated elements not observed. Pileipellis a cutis, with transition to a trichoderm. In water, the disc has two types of hyphae, some cylindrical, very thin, not or slightly narrow at the septa with incrusted parietal pigment, 2–4 μm wide and others cylindrical, very narrow at the septa, consisting of short fusiform or doliiform elements, 3–10 μm, with abundant granular pigment in the form of large dark brown granules that can fill the entire elements; and outside the disc hyphae are similar to these of the disc but with the elements more cylindrical and greater abundance of hyaline elements lacking the granular pigments. Clamp connections not observed.

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

Habit, habitat, occurrence and distribution: In groups of few basidiomata, in broadleaf forests. Rare. Recorded only from the Dominican Republic and Mexico.

Species-specific ITS markers in A. sect. Xanthodermatei : ggataAgagga@146, ccttaCagaaa@236, tgttcYgcttc@618.

Note: The Mexican collection was missing after microscopical examination and a mycelial culture was obtained. It had spores 3.4–5.7 × 3.4–4.6 μm, and cheilocystidia 5.7–6.8 × 5.7–8.0 μm. The mycelium of the Mexican collection grew very slowly at 25°C on compost extract medium, failing to fruit after 6 months of culture with the standard protocol used for A. bisporus (J.E. Lange 1926: 8) Imbach (1946: 15) , modified as follow: compost supplemented with glucose (10 g /l) and sterilized, axenic culture until complete compost invasion.

Material examined: DOMINICAN REPUBLIC, Puerto Plata, Sosúa, Puerto Chiquito, 25 November 2011, JBSD 123822, Holotypus ( LAPAM 18, Isotypus ). MEXICO, Veracruz, Xalapa, INECOL-Instituto de Ecologia, A. C., Jardín Botánico Francisco Javier Clavijero, cloud forest (locally called “bosque mesófilo de montaña”) dominated by Platanus mexicana and Liquidambar styraciflua , in botanical garden, 20 August 2007, collectors M. Nau and C. Billette, Mata & Billette 745 ( XAL, missing collection), mycelial strain IE 786 ( XAL) duplicate CA 595 ( CGAB), GenBank ITS sequence: HQ322269.

Taxonomic comments: The most similar species to A. tephrolepidus are A. endoxanthus , A. moelleri , A. moelleroides , A. punjabensis and A. volvatulus , but all these species have a bright yellowing discoloration in the context of the stipe base when cut (except A. punjabensis , for which this character was not described) and spores with very different sizes. Furthermore, in A. endoxanthus and A. volvatulus the pileipellis consists of elements with abundant vacuolar pigment and A. volvatulus lacks cheilocystidia. Within the Caribbean region, A. griseorimosus Pegler (1983: 435) , described from the island of Martinique, has a very similar aspect according to the drawings and photographs provided by Pegler (1983) and also lacks the yellowing in the context of the stipe base when cut and has a strong odor of “iodine”. Therefore, even if this author included this species in A. sect. Agaricus , in our opinion and according to the characters of the original description, A. griseorimosus more likely belongs to section Xanthodermatei . However, this species has a rimose pileus, a simple annulus and much longer and narrower spores (5.3–5.6–7.5 × 2.7–3.0–3.5 μm) with a Q value of 1.8, very different from those of A. tephrolepidus .

Figures

FIGURE 21. Macroscopic characters of A. tephrolepidus. A–E. Basidiomata. A–B. (JBSD123822, holotype); C–E. (Mata & Billette 745). Microscopic characters of A. tephrolepidus (F–I, K–L in ammoniacal Congo red; J in water). F–L. (JBSD123822, holotype). F. Cheilocystidia. G. Basidia. H. Spores. I. Hyphae of the lower surface of the annulus (terminal hyphae are marked with an asterisk). J–L. Pileipellis hyphae (one terminal hypha). Photos by C. Angelini (A–B, F–G), C. Billette (C–E) and L.A. Parra (H–K).