Agaricus xalapensis Guzmán-Guillermo, Linda J. Chen & Llarena-Hernández, sp. nov.
Creators: name: Guzmán-Guillermo, Jorge
name: Chen, Jie
name: Enríquez-Bedolla, José Carlos
name: Ortega, Iván Oros-
name: Zetina-Córdoba, Pedro
name: Núñez-Pastrana, Rosalía
name: Llarena-Hernández, Régulo Carlos
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Fungi
Basidiomycota
Agaricomycetes
Agaricales
Agaricaceae
Agaricus
Agaricus xalapensis

description: Agaricus xalapensis Guzmán-Guillermo, Linda J. Chen & Llarena-Hernández sp. nov. (Figs. 4, 5)   
MycoBank: MB854095  
Etymology:—The epithet refers to the type locality in Xalapa, Mexico.  
 Macroscopic description:— Pileus 5–12 cm diam., conical-truncate to convex when young, then plano-convex, finally plane at maturity, covered by light yellowish brown to brownish appressed-fibrillose scales on cream whitish background, denser at center. Surface dull and dry. Margin slightly exceeding the lamellae. Lamellae free, straight, intercalated with numerous lamellulae, white for a long time, staining pinkish after handled, then greyish pink, finally dark brown at maturity. Stipe 4.8–11.5 × 0.6–1.4 cm (up to 2.1 cm at base), cylindrical to clavate, and sometimes with a bulbous base, fistulose when young, with an annulus in its upper third, above annulus smooth and white, below annulus covered with concolor tiny erected-fibrillose scales, faintly yellowish when bruised. Annulus superous, double, white, usually thick, upper surface smooth, lower surface covered with brownish or white scales, often forming a cogwheel at the margin. Context cream white, firm, yellowish when exposed. Odor of bitter almonds.   
 Microscopic description:— Basidiospores (4.6–)4.8–5.5 (–6.1) × (3.3–)3.6–4.4 μm, (x = 5.1 × 3.9 μm, Q = 1.14– 1.51, Qm = 1.31), broadly ellipsoid to ellipsoid, smooth, brown, without apical pore. Alongside these spores, there are a few giant spores of 6.4–7.4 × 4.1–5.5 μm, ellipsoid. Basidia 23–25 × 9–11 μm, tetrasporic, clavate, hyaline, smooth. Cheilocystidia abundant, hyaline, simple or septate at the base, clavate to broadly clavate, pyriform, 14–32 × 8–14 μm. Pleurocystidia not observed. Lower surface of the annulus composed of two types of hyaline hyphae, cylindrical, not or slightly narrowed at septa, 3–10 μm wide; and others, generally consisting of globose, spherical, ovoid or peanutshaped inflated elements readily disarticulating, up to 10 μm wide. Pileipellis a cutis composed of cylindrical and thin-walled hyphae of 3.5–7 μm wide, hyaline or with light brownish membranous pigment, slightly constricted at the septa, or sometimes very narrow at the septa, consisting of short fusiform or doliiform elements, 6–13 μm wide. Clamp connections not observed.   
Macrochemical reactions:—Schäffer’s reaction positive, orangish red. KOH reaction positive, yellow.  
 Habit and habitat:—gregarious on leaf litter of Bambusoideae spp., Casuarina equisetifolia and ant nest below Inga jinicuil.   
Material examined:— MEXICO, Xalapa, Universidad Veracruzana, Zona Universitaria, 8 September 2021, Guzmán-Guillermo, J2367 (Holotype, XAL); Xalapa, Universidad Veracruzana, Facultad de Ingeniería, 12 September 2021, Guzmán-Guillermo, J2883; Xalapa, Circuito Presidentes, Parque La Loma, 18 September 2022, Guzmán-Guillermo, J2946, J2947, J2953; Xalapa, Universidad Veracruzana, Zona Universitaria, 24 October 2022, Guzmán-Guillermo, J3004.  
 Notes: Agaricus xalapensis is characterized by its medium to large-sized basidiomata, the pileus covered with light yellowish brown to brownish appressed-fibrillose scales, the tiny erected-fibrillose scales on the stipe surface below the annulus, the double annulus, and the odor of bitter almonds.   
 Morphologically, A. xalapensis is most like A. ficophilus Heinem. (1961: 241) by having the dense scaly coating of both pileus and stem and in tones of yellowish brown (Heinemann 1961). However, A. ficophilus differs from A. xalapensis by its large central umbo, and slightly larger spores, 5–6 × 3.2–4.2 μm (Heinemann 1961). Agaricus rufoaurantiacus Heinem. (1961: 242) is another species morphologically very similar. However, according to the description and illustrations of the samples made from Dominican Republic (Parra et al. 2018), it differs by its minute warty squamules with ochre orange tones never observed in A. xalapensis. Molecular analysis shows that it is nested in a clade clearly separated from A. xalapensis (Fig. 1).
description: Published as part of Guzmán-Guillermo, Jorge, Chen, Jie, Enríquez-Bedolla, José Carlos, Ortega, Iván Oros-, Zetina-Córdoba, Pedro, Núñez-Pastrana, Rosalía & Llarena-Hernández, Régulo Carlos, 2024, Morphological characteristics and phylogenetic analyses revealed two new species of Agaricus subg. Minoriopsis from Mexico, pp. 65-78 in Phytotaxa 655 (1) on pages 70-74, DOI: 10.11646/phytotaxa.655.1.5, http://zenodo.org/record/13217199