Entoloma arion O.V. Morozova, E.S. Popov, T.H.G. Pham & 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 : 10-13

Entoloma arion O.V. Morozova, E.S. Popov, T.H.G. Pham & Noordeloos , sp. nov. (Figs. 5, 6)

Mycobank: MB 843251

Type:— VIETNAM. Gia Lai Province, K’Bang District, Son Lang Commune , Kon Chu Rang Nature Reserve , N 14.487996°, E 108.57101°, 960 m a.s.l., on soil along a track in middle-mountain evergreen mixed forest with a predominance of Podocarpaceae ( Dacrydium elatum , Dacrycarpus imbricatus ), Magnoliaceae , Burseraceae ( Canarium) , Myrtaceae ( Syzygium) , 29 May 2016, O.V. Morozova and E.S. Popov (holotype: LE F-312691 (!), isotype in VRTC (!), ITS sequence GenBank OM987259 , LSU sequence GenBank OM996176 ).

Etymology:—Ἀρίων (Greek), Aríon (Lat.) a Greek poet, singer and musician who played the cithara (7–6th centuries BC). According to legend, Arion sailed with rich treasures on a ship to Corinth. The sailors, wanting to take possession of the singer’s wealth, threw him overboard, but Arion was rescued by a dolphin and safely reached Corinth. A butterfly Phengaris arion of the Lycaenidae (Cupidinidae) family with a blue upper and a light under surface of the wings was named after him. Our new species is similar to it in colors.

Diagnosis:— Entoloma arion is characterized by the bright blue, radially fibrillose pileus with rather dark blue central spot and scales at first densely covering whole surface, moving apart with pileus expansion, showing a whitish or light blue background, and a white stipe that is minutely innately fibrillose and pruinose at the apex. Microscopically, cylindrical to broadly clavate septate cheilocystidia and caulocystidia in the form of bundles of long hairs are distinctive.

Description:— Basidiomata small to medium-sized, collybioid. Pileus 10‒25 mm diam., hemisphaerical, convex, soon expanding to plano-convex with flat to slightly depressed centre, with deflexed then straight margin, non hygrophanous, non translucently striate, radially fibrillose, at first entirely densely covered with dark blue to blackish blue squamules (20E–F6–8), moving apart with pileus expansion showing whitish or light blue (20B–C4–6) background, with fibrillose, contrasting blackish blue centre. Lamellae moderately distant, broadly adnate, slightly emarginate with a small tooth, segmentiform to arcuate, white, or pale bluish in young basidiomata, becoming pinkish, with irregular concolorous edge. Stipe 30–70 × 1.5–2 mm, cylindrical, minutely innately fibrillose, pruinose in upper part, translucent, white or pale bluish in young basidiomata. Context white. Smell indistinct, taste not reported.

Basidiospores (9.5–)10.5–12(–13) × (6.5–)7–7.5(–8.5) μm, Q = (1.3–)1.5(–1.7), heterodiametrical, with 5–6 angles in side-view. Basidia 23–30 × 9–12 μm, 1–2-or 4-spored, narrowly clavate to clavate, clampless. Cheilocystidia 27–78 × 7–18 μm, cylindrical or narrowly to broadly clavate, often septate, not pigmented, forming a sterile lamellar edge or intermixed with basidia. Pileipellis a cutis with transition to a trichoderm, composed of repent cylindrical hyphae 4–8 μm diam with narrowly clavate to fusoid ascending terminal elements 70–210 × 15–25 μm, a trichoderm at center. Caulocystidia in the form of bundles of hairs up to 200 μm long composed of chains of cylindrical cells 23–44 × 5–10 μm. Clamp connections absent.

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

Additional specimens examined:— VIETNAM. Gia Lai Province, K’Bang District, Son Lang Commune, Kon Chu Rang Nature Reserve, N 14.49776°, E 108.556993°, 975 m a.s.l., on soil along a track in middle-mountain evergreen mixed forest with a predominance of Podocarpaceae ( Dacrydium elatum , Dacrycarpus imbricatus ), Magnoliaceae , Burseraceae (Canarium) , Myrtaceae (Syzygium) , 28 May 2016, O.V. Morozova and E.S. Popov (LE F-312692 (!), ITS sequence GenBank OM987260 ; LE F-315917 (!), ITS sequence GenBank OM987261 ).

Notes:— Entoloma arion can be easily recognized by the bright blue pileus and contrasting white stipe, a very rare combination in subgenus Cyanula . Entoloma floccosodentatum Corner & E. Horak , in Horak (1980: 288) from New Caledonia is superficially similar in colors, spore size and cystidia form, but its pileus is pale blue and smooth, or only innately fibrillose, or tomentose. The presence of clamps on the hyphae indicates that Entoloma floccosodentatum does not belong to the subgenus Cyanula . Geographically it is also very distant and isolated.