Agaricus rufoaurantiacus Heinem., Kew Bull.

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 : 249-252

Agaricus rufoaurantiacus Heinem., Kew Bull. 15(2): 242, 1961. ( Figs. 13–14 )

Macroscopic description: Pileus (2.5–)3.0–4.0(–5.5) cm diam., at first hemispherical then plano-convex (rarely trapezoid), completely plane at maturity, entirely covered by minute warty ochre orange squamules on whitish background, with an entire orange or reddish orange center. Surface dull and dry. Margin not exceeding the lamellae, often appendiculate because of the annulus remnants, sometimes slightly striate at maturity. Lamellae free, slightly ventricose, intercalated with numerous lamellulae, white for a long time, staining intensely pink after handled (resembling at first glance a species of Leucoagaricus ), then brown, blackish brown at maturity with a paler and even edge. Stipe (4.0–)5.0–5.5(–6.0) × 0.4–0.6 cm (up to 1 cm at base), cylindrical, usually tapered at apex and bulbous towards base, fistulose, with an annulus in its upper third, above annulus with white fibrils becoming grayish with age, below annulus fibrillose, covered by large orange or ochre orange scales especially at the base, sometimes forming bands, in rare cases entirely covering the stipe and the lower surface of the annulus, strongly yellowing on handling, with a single and thick central rhizomorph at the base. Annulus superous, double, white, up to 0.7 cm broad, usually thick and persistent, upper surface strongly striate, lower surface covered by thick ochre or orange scales often forming a cogwheel at the margin. Context moderately dense in the center of the pileus, scanty at the margin, when cut at first white then yellowing, with odor of bitter almonds.

Microscopic description: Spores (4.12–)4.22–4.85–5.36 × 3.10–3.46–3.90(–4) μm, Q=1.26–1.41–1.65, ellipsoid, smooth, brown, without apical pore. Basidia 13–18(–23) × 6–8 μm, tetrasporic, clavate or slightly truncated at the apex, sterigmata up to 3 μm long. Cheilocystidia highly variable in quantity and shape in different collections. In some collections abundant and very conspicuous, in others only a few in small fascicles and in others very rare and difficult to distinguish from basidioles, usually hyaline but also sometimes with a brown diffuse internal pigment, simple or septate at the base, with terminal elements pyriform, clavate, cylindrical (usually with some constrictions), fusiform, fusiform-subcapitulate or capitulate, rostrate, mucronate or more rarely with lateral digitiform appendages, 9–24 × 4–11 μm; anteterminal elements in the septate ones more or less cylindrical of 5–13 × 4.5–6.5 μm. Pleurocystidia not observed. Lower surface of the annulus consisting of two types of hyphae, some cylindrical with a constant diameter composed of long elements of 2–6 μm wide, rare, and others clearly narrowed at septa with short elements of 2–7 μm wide. Terminal elements cylindrical or progressively attenuated towards the rounded apex. Inflated elements not observed. Pileipellis a cutis, with transition to trichoderm in the squamulose disc. In the disc predominate hyphae narrower at septa with short elements of 2–7 μm wide, terminal elements abundant, cylindrical or progressively attenuated towards the rounded apex, and outside of the disc predominate cylindrical hyphae with constant diameter composed of long elements 2–6 μm wide. In water, all hyphae contain abundant granular pigment (more in the disc), with golden yellow granules up to 3 μm wide. Clamp connections not observed.

Macrochemical reactions: Schäffer’s reaction positive, slow but intense, dark reddish purple. KOH reaction difficult to read because of the orange yellow color of the exsiccatum.

Habit, habitat, occurrence and distribution: Solitary or in small groups of 2–3 basidiomata, in all types of broadleaf forests. According to our data, this is the most common Agaricus species in the Dominican Republic. The holotype (Dennis 241) and a paratype (Dennis 328) of this species were collected by R. W. G. Dennis in the Caribbean island of Trinidad ( Heinemann 1961). Pegler (1983) also reports it from Martinique.

Note: This species is characterized by its small to medium size, the pileus covered with minute orange ochre appressed squamules with the disc intensely colored, the lamellae that remain white for a long time and stain rose on handling (resembling a species of Leucoagaricus at this stage), the stipe and lower surface of the annulus covered by thick scales colored orange ochre, sometimes forming basal bands, the double annulus, the odor of bitter almonds and the evident long basal rhizomorph.

Material examined: DOMINICAN REPUBLIC, Puerto Plata, Sosúa , beach, 27 November 2011, JBSD123818 ( LAPAM15 ) ; Puerto Plata, Sosúa , beach, 21 November 2013, JBSD126470 ( LAPAM29 ) ; Puerto Plata, Sosúa , beach, 22 November 2013, JBSD126471 ( LAPAM30 ) ; Puerto Plata, Sosúa , beach, 25 November 2013, JBSD126472 ( LAPAM31 ) ; Puerto Plata, Sosúa , beach, 10 December 2013, JBSD126473 ( LAPAM32 ) ; Puerto Plata, Sosúa , beach, 19 December 2013, JBSD126474 ( LAPAM33 ) ; Puerto Plata, Sosúa , beach, 27 November 2014, JBSD126475 ( LAPAM54 ) ; Puerto Plata, Sosúa , cemetery, 3 December 2013, JBSD126476 ( LAPAM36 ) ; Puerto Plata, Sosúa , cemetery, 14 December 2014, JBSD126477 ( LAPAM51 ) ; Sosúa, Puerto Chiquito , 5 December 2014, JBSD126478 ( LAPAM59 ) ;

Taxonomic comments: The closest known species to A. rufoaurantiacus is undoubtedly A. ochraceosquamulosus Heinem. (1961: 243) , described from a single collection, made on the island of Trinidad, that consists of only two basidiomata growing together.From the study of the original descriptions and illustrations of both species by Heinemann (1961), A. ochraceosquamulosus is distinguished from A. rufoaurantiacus by its less vivid colors on both the surfaces and context, the narrow and fragile annulus, the larger spores (5.1–5.7 × 3.6–4.0 μm) and the positive Schäffer’s reaction. Based on the study of our collections, however, we found that the color of the basidiomata of A. rufoaurantiacus is variable depending on its age or if it is wet from rainwater. Similarly, the annulus in A. rufoaurantiacus seems simple and fragile on the stipe if broken at its middle part leaving appendiculate remnants with the scales of its lower surface in the pileus margin. Regarding the Schäffer’s reaction, our collections of A. rufoaurantiacus show a dark purple red reaction matching well with what Pegler (1983) observed for this species. Heinemann (1961) in his original description indicated a negative Schäffer’s reaction but later ( Heinemann, 1962a), noted that this species may also have positive reaction. Thus, the spore sizes are the only remarkable difference between the two species since both the measurements obtained by Heinemann (4.0–5.0 × 2.9–3.8 μm) and us after the study of the 10 Dominican collections (4.12–4.83– 5.36 × 3.10–3.42–4 μm) are significantly smaller than those of A. ochraceosquamulosus , although there is a small range of overlap, especially in collection LAPAM 36 that has larger spores (4.94–5.11–5.25 × 3.30–3.58–3.91 μm). Therefore, although we think that there is a possibility that these species are synonymous, we prefer to keep them as separate species because of their different spore size until more collections of A. ochraceosquamulosus can be found and studied or the type specimen sequenced.

Agaricus ficophilus Heinem. (1961: 241) is, according to this author, another very similar species, but this taxon has the pileus and stipe below annulus covered by scales with brown tones never observed in A. rufoaurantiacus , neither in the collections described by Heinemann (1961) nor in our collections. Additionally, the spores of A. ficophilus are clearly longer (5.0–6.0[–6.5] × 3.2–4.2 μm) than in A. rufoaurantiacus .

Pegler (1983) also explicitly indicated that A. rufoaurantiacus , A. ochraceosquamulosus and A. ficophilus “are closely related species with variable characters”. In our opinion, their possible synonymy can be definitively confirmed only by molecular methods.

Additional comments: Some phylogenetic comments on this species are included under Agaricus sp. LAPAM 48 from hybrid origin.

Figures

FIGURE 13.Macroscopiccharactersof A.rufoaurantiacus.A–H. Basidiomata.A.(JBSD123818);B.(JBSD126473);C,H.(JBSD126476); D. (JBSD126477); E. (JBSD126478); F. (JBSD126475); G. (JBSD126474). Photos by C. Angelini.

FIGURE 14. Microscopic characters of A. rufoaurantiacus. A–K. (A–G, I, K in ammoniacal Congo red; H, J in water).A. (JBSD126472), B–D. (JBSD126473) E. (JBSD123818), F. (JBSD126471), G. (JBSD126475), H–K. (JBSD126474). A–D. Cheilocystidia. E. Basidia. F. Spores. G. Hyphae of the lower surface of the annulus. H–K. Pileipellis hyphae (H–I discal area, J–K medial area). Photos by L.A. Parra.