Entoloma argus O.V. Morozova, E.S. Popov, A.V. Alexandrova & Noordeloos, 2022

Morozova, Olga, Popov, Eugene, Alexandrova, Alina, Pham, Thi Ha Giang & Noordeloos, Machiel Evert, 2022, Four new species of Entoloma (Entolomataceae, Agaricomycetes) subgenera Cyanula and Claudopus from Vietnam and their phylogenetic position, Phytotaxa 549 (1), pp. 1-21 : 8-10

Entoloma argus O.V. Morozova, E.S. Popov, A.V. Alexandrova & Noordeloos , sp. nov. (Figs. 3, 4)

Mycobank: MB 843250

Type:— VIETNAM. Gia Lai Province, K’Bang District, Son Lang Commune , Kon Chu Rang Nature Reserve , N 14.505520°, E 108.541610°, 1050 m a.s.l., on soil in middle-mountain evergreen mixed forest with a predominance of Podocarpaceae ( Dacrydium elatum , Dacrycarpus imbricatus ), Magnoliaceae , Burseraceae ( Canarium) , Myrtaceae ( Syzygium) , 26 May 2016, O.V. Morozova (holotype: LE F-312694 (!), isotype in VRTC (!), ITS sequence GenBank OM987263 , LSU sequence GenBank OM996175 ).

Etymology:—Ἄργος (Greek), Argus (Lat.) a character from ancient Greek mythology. Argos was a one hundred-eyed giant who paid a service to the goddess Hera. Zeus killed the giant, but Hera remembered the giant by placing his one hundred eyes on the tail of the peacock. His name is used in various combinations in the generic and species names of butterflies of the Lycaenidae (Cupidinidae) family. The new Entoloma species is named after the butterfly Plebejus argus , due to the similarity of color.

Diagnosis:— Entoloma argus is characterized by the delicate greyish blue basidiomata with the distinctly translucently striate pileus covered by small dark blue squamules on a paler greyish blue background with contrasting dark blue centre, and the smooth, polished stipe concolorous with pileus. Microscopically, the sterile lamella edge of cylindrical to narrowly clavate colorless cystidia, and rather small 5–6 angled spores are characteristic.

Description:— Basidiomata small to medium-sized, collybioid. Pileus 15‒25 mm diam., hemispherical to convex soon expanding to plano-convex with flat to slightly depressed centre, with deflexed then straight margin, hygrophanous, translucently striate almost up to the centre, greyish blue (21C–D4–7), covered with dark blue squamules, glabrescent with age and discoloring to greyish beige, with dark blue (21F6–8) fibrillose center. Lamellae moderately distant, adnate-emarginate, ventricose, white, becoming pinkish, with entire edge concolorous with faces. Stipe 30–60 × 1–1.5 mm, cylindrical, smooth, polished, greyish blue, concolorous with pileus (21C–D4–7), with white tomentum at base. Context white, greyish under the surface. Smell indistinct, taste not reported.

Basidiospores (8.5–)9.5–10(–11.4) × (6.0–)6.5–7(–7.5) μm, Q = (1.3–)1.45–1.5(–1.6), heterodiametrical, with 5–6 angles in side-view. Basidia 24–34 × 8.5–11.5 μm, 1–2-spored or 4-spored, narrowly clavate to clavate, clampless. Cheilocystidia 33–53 × 7.5–14 μm, cylindrical to narrowly clavate, sometimes septate, not pigmented, forming a sterile lamellae edge. Pileipellis a cutis of cylindrical hyphae 2–7 μm diam with trichodermal bundles of ascending hyphae with cylindrical to narrowly clavate terminal elements (46–86 × 14–20 μm) forming the macroscopic squamules and central disk of pileus. Clamp connections absent.

Habitat and distribution:—In small groups in middle-mountain evergreen mixed forests. Known from Vietnam.

Additional specimens examined:— VIETNAM. Gia Lai Province, K’Bang District, Son Lang Commune, Kon Chu Rang Nature Reserve, on soil in middle-mountain evergreen mixed forest with a predominance of Podocarpaceae ( Dacrydium elatum , Dacrycarpus imbricatus ), Magnoliaceae , Burseraceae (Canarium) , Myrtaceae (Syzygium) , path to the waterfall, N 14.51361°, E 108.54621°, 1007 m a.s.l., 25 May 2016, A. Alexandrova ( LE F-315916 (!), ITS sequence GenBank OM 987264 ); ibid., N 14.505520°, E 108.541610°, 1050 m a.s.l., 28 May 2016, I. Semenyuk and E. Popov ( LE F-312695 (!), ITS sequence GenBank OM 987262 ); ibid., on the river bank, 28 May 2016, O. V. Morozova ( LE F-315915 (!), ITS sequence GenBank OM 987265 ).

Notes:— Entoloma argus is distinguished from the macromorphologically similar E. ekaterinae O.V. Morozova, Noordel., K. Nara, Dima & Brandrud, in Crous et al. (2019: 413) from the Russian Far East by the more applanate pileus, different pileipellis structure and shape of the cheilocystidia (cylindrical vs. broadly clavate and subglobose). E. subcaesiellum Noordeloos & O.V. Morozova (2010: 243) also described from the Russian Far East possesses a less squamulose pileus with blue squamules on a greyish beige background and microscopically lacks a distinct trichoderm at pileal center. The European E. phaeodiscum Vila & F. Caballero (2007: 41) differs by the absence of cheilocystidia, less pronounced, fading blue coloration, and geographical distribution.