Agaricus argenteopurpureus L.A. Parra, Angelini & 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 : 240-243

Agaricus argenteopurpureus L.A. Parra, Angelini & Callac , sp. nov. ( Figs. 8–9 )

MycoBank: MB823280.

Etymology: for the violet purple color (in Latin “ purpureus ”) with silver (in Latin “ argenteus ”) highlights on the pileus.

Original description, Macroscopic description: Pileus (2.5–)3.0–3.5(–4.0) cm diam., at first conicohemispherical, then quickly plano-convex or plane with a slightly revolute margin; frequently depressed at center, more rarely with a broad umbo at center and depressed at the peridiscal area, grayish with silver highlights, covered partially or entirely with purple fibrils that tend to merge simulating squamules, closer and appressed at disc where it is very dark purple vinaceous. Surface smooth, fibrillose, dry and dull. Margin fine, not exceeding the lamellae, not striate in immature or young basidiomata but strongly striate or rimose, in mature basidiomata or after rain. Lamellae free, slightly ventricose, intercalated with numerous lamellulae, at first very pale, grayish pink, then brownish pink, finally dark grayish brown, with a paler and slightly eroded edge. Stipe 3.5–4.5 × 0.3–0.4 cm, cylindrical and straight, clavate or slightly bulbous at base, at times also marginately bulbous, fistulose, with an annulus in the upper third, smooth to somewhat fibrillose, gray, grayish purple above the annulus, fibrillose and whitish below annulus, yellowing on handling particularly towards the base, base with a central, not or branched rhizomorph. Annulus superous, double, white, up to 0.5 cm broad, fine, thicker at the margin, pendulous, soon adpressed to the stipe, upper surface smooth or finely striate and the lower surface finely fibrillose-squamulose. Context slightly dense, scanty at the pileus margin, when cut at first white then light ochre, especially at the stipe apex, with odor of bitter almonds.

Microscopic description: Spores 4.74–5.09–5.67 × 3.19–3.57–4 μm, Q=1.27–1.43–1.63, ellipsoid, smooth, brown, without apical pore. Basidia 15–23(–27) × 6.5–8(–12) μm, tetrasporic, clavate or slightly truncated at the apex, sterigmata up to 3 μm long. Cheilocystidia abundant, hyaline and smooth, simple or with a basal septum. Terminal elements generally clavate, broadly clavate or pyriform, often also fusiform or rostrate, rarely capitulate, 10–27(–32) × 6–15 μm. Anteterminal elements in those septate more or less cylindrical 5–15 × 3.5–8 μm. Pleurocystidia not observed. Lower surface of the annulus consisting of cylindrical hyphae, not or slightly narrowed at the septa, some with encrusted parietal pigment, 2–7 μm wide. Inflated elements not observed. Pileipellis a cutis composed of cylindrical hyphae of 3–10 μm wide, the wider the more constricted at septa. In water, hyphae from the disc with abundant pink diffuse pigment and with punctate granular pigment, in a few elements; outside of the disc hyaline or few elements with well-diffused pink or granular punctate pigment. Terminal elements abundant, cylindrical or attenuated at the apex, which is rounded. Clamp connections not observed.

Macrochemical reactions: Schäffer’s reaction positive, color dark reddish purple. KOH reaction positive, color orange yellow.

Habit, habitat, occurrence and distribution: Solitary, rarely in groups of a few basidiomata, in broadleaf forests. Common. Recorded only from the Dominican Republic.

Species-specific ITS markers in A. subg. Minoriopsis: cacgcTtgtttggaAttcat@54–63, gtgtgCaaact@166, tacccAgtcga@238, and tgaaaAgcatt@544.

Note: This species is characterized by its medium-small size, its solitary basidiomata, the pileus with gray with silver highlights and dark reddish purple disc, the pileal margin striate and eroded at maturity, the double annulus with thick margin, the quick yellowing reaction on the stipe on handling, the central rhizomorph at the stipe base and the odor of bitter almonds.

Material examined: DOMINICAN REPUBLIC, Puerto Plata, Sosúa , beach, 22 December 2012, JBSD126500 ( LAPAM24 ) ; Puerto Plata, Sosúa , beach, 25 November 2013 JBSD126501 Holotypus ( LAPAM28 Isotypus ) ; Puerto Plata, Sosúa , beach, 27 November 2014, JBSD126502 ( LAPAM53 ) ; Puerto Plata, Sosúa , beach, 28 November 2014, JBSD126503 ( LAPAM55 ) .

Taxonomic comments: This species is highly similar to A. martinicensis , from which it differs in smaller size, a pileus surface that is usually more grayish silver toward the margin and more frequently striate, and smaller spores, although an unambiguous identification would require the use of molecular characters to unequivocally differentiate the two species.

This species is also macroscopically similar to many species of A. subg. Minores in the pileus completely covered by reddish purple squamules, but it is distinguished by its membranous double annulus that is thicker at the margin with the lower surface fibrillose-squamulose and its dark reddish purple Schäffer’s reaction in dried material, instead of a simple annulus that is fragile and ephemeral and the weak reddish pink Schäffer’s reaction in dried material of A. subg. Minores . Within A. sect. Pantropicales, Agaricus argenteopurpureus , at times, strongly resembles to A. porphyropos , but the former has a pileus with silvery or greyish highlights which is reddish purple on a white background in all studied collections of A. porphyropos . However, we must be cautious when using these characters to separate the two taxa since we do not well know the variability in A. porphyropos .

Agaricus argenteopurpureus also resembles macroscopically A. dennisii Heinem (1961: 245) , a species placed by this author in A. subg. Conioagaricus Heinem. (1956: 101). Their pilei have the same color and, in mature basidiomata, the same strongly striate margin, which exudes reddish drops. However, A. dennisii lacks an anise odor, its Schäffer’s reaction is negative, it lacks cheilocystidia and its spores are much smaller with dimensions not overlapping with those of A. argenteopurpureus .

Figures

FIGURE 8. Macroscopic characters of A. argenteopurpureus. A–F. Basidiomata.A–B. (JBSD126500); C, F. (JBSD126501, holotype); D. (JBSD126502); E. (JBSD126503). Photos by C. Angelini.

FIGURE 9. Microscopic characters of A. argenteopurpureus. A–H. (JBSD126501, holotype) (A–G in ammoniacal Congo red; H in water). A–C. Cheilocystidia. D. Basidia. E. Spores. F. Hyphae of the lower surface of the annulus. G–H. Pileipellis hyphae. Photos by L.A. Parra.