Volvariella orientalis E.F. Malysheva, E.S. Popov & A.V. Alexandrova, 2022

Malysheva, Ekaterina & Popov, Eugene, 2022, Observations on Pluteaceae in Vietnam. 3. One new species of Volvariella, Phytotaxa 545 (3), pp. 278-286 : 282-284

Volvariella orientalis E.F. Malysheva, E.S. Popov & A.V. Alexandrova , sp. nov. ( Fig. 2 )

MycoBank MB 841914

Diagnosis: —Basidiocarps large and stout, pileus pilose-squamulose, pale brownish grey or ochre brown, volva spacious, saccate, ochre brown or with olive tint, with velvety outer surface; basidiospores 7.5–8.5(9.3) × 5.0–6.0(6.4) µm, broadly ellipsoid to ovoid, cheilocystidia lageniform or fusiform, with apical papilla (mucronate), caulocystidia numerous; grow on rotten wood or litter.

Type: — VIETNAM. Nghe An Province, Con Cuong District, Chau Khe commune, 2.5 km WNW of Khe Choang ranger station, Pu Mat National Park , 18°57’48.204’’N, 104°39’43.524’’E, h = 457 m. a.s.l., disturbed lowland tropical broadleaved monsoon forest, on strongly rotten banana debris, 18 April 2018, E. Popov ( LE 313654!; GenBank: OL415619 – nrITS, OL415617 – nrLSU, OM 948984 – tef1) .

Etymology: —The name refers to geographical distribution.

Basidiocarps large, fleshy. Pileus 60–110 mm diam., initially broadly campanulate, then convex to applanate with broad umbo, with even incurved non-striate margin; non-hygrophanous; surface dry, pilose-squamulose, covered with silk grey (RAL 7044), pebble grey (RAL 7032) or ivory (RAL 1014) squamules, scarce at margin and more dense and dark-coloured (ochre yellow - RAL 1024, olive brown – RAL 8008) at centre, with silver-white or yellowish background. Lamellae rather crowded, free, with lamellulae, ventricose, pinkish, spotted, with whitish undulating edge. Stipe 40–65 × 7–10 mm, cylindrical, broadening towards base (up to 20 mm), solid, grey white (RAL 9002) or oyster white (RAL 1013); longitudinally fibrillose. Volva spacious, saccate, bilobed, rather thick, ochre brown (RAL 8001) or olive brown (RAL 8008), with velvety surface. Context white. Smell and taste indistinct.

Basidiospores [60, 1, 1] 7.5–8.5(9.3) × 5.0–6.0(6.4) µm (L av = 8.3 µm, W av = 5.7 µm, Q = (1.3)1.4–1.6(1.7), Q av = 1.5), ellipsoid to broadly ellipsoid or ovoid, hyaline in KOH, thick-walled. Basidia 24–30(40) × 7–10 µm, 4- spored, broadly clavate, often inflated in the middle. Cheilocystidia (40)57–93(110) × 13.5–20(40) µm, numerous, forming a sterile lamella edge, ventricose-fusiform, broadly lageniform, often with apical papilla (mucronate), thin- or slightly thick-walled, hyaline in 3% KOH, often with granular content. Pleurocystidia 40–80(98) × 13–20(28) µm, rather abundant, ventricose-fusiform or lageniform with obtuse or subcapitate apex, slightly thick-walled, hyaline in 3% KOH. Lamella trama composed of hyaline hyphae 3–7 µm wide, thin-walled. Pileipellis a cutis, transforming into a trichoderm, made up of thin- or slightly thick-walled, non-gelatinous hyphae, 15–20(30) µm wide, hyaline or yellowish; ascending terminal elements are cylindrical or fusiform with acuminate or mucronate apex, 70–200(290) µm long. Stipitipellis a cutis, compose of long, cylindrical, hyaline hyphae, 8–10 µm wide. Caulocystidia rather numerous, 30–84(92) × (5.5)7.0–18 µm, in bundles, cylindrical, fusiform or lageniform, hyaline, thin-walled. Clamp connections absent in all tissues examined.

Habitat and known distribution: —Solitary, on banana litter in woody area. So far known only from two provinces of Vietnam located in central and southern parts of the country.

Additional specimen examined: — VIETNAM. Central Highlands region (Tây Nguyên), Kon Tum Plateau, Gia Lai Province, Mang Yang districts, A Yun commune, A Yun village, Kon Ka Kinh National Park , 45 km northeast of the city Pleiku , 35 km east of the city Kon Tum, bank of the stream, 14°12’14.6376’’N, 108°17’51.2088’’E, banana grove, on banana litter, 21 May 2016, A. Alexandrova ( LE 313241!, GenBank: MK 882999 – nrITS, MK 883004 – nrLSU, MK 940803 – tef1) .

Notes: —During the expedition to Vietnam in 2016, one specimen of a presumably unknown species was collected. Thorough morphological and molecular study has shown its uniqueness and independent taxonomic status ( Malysheva et al. 2019). However, this specimen was immature, and then we could not study in detail the features of basidiospores. Another collection, found by one of the co-authors (E. Popov) in Nghe An province of Vietnam in 2019, turned out to be identical to the previous one. This made it possible to clarify the lacking morphological characteristics. Here we describe a new species, providing an amended and combined description based on the two studied collections.

The macroscopic characteristics of our collections mostly agree with the description of Volvariella bombycina in terms of stout basidiocarps with light-coloured pale brownish and entirely squamulose pileus, thick stipe, and spacious brown volva. At the same time, the microscopic characters, such as the size of basidiospores and the peculiar form of cheilocystidia with the apical papilla, make it close to V. volvacea . Volvariella orientalis differs from V. bombycina in velvety outer surface of volva and broader hymenial cystidia with subcapitate apex, and it mainly differs from V. volvacea in pilose-squamulose pileus, ochre brown or olive brown volva and the presence of caulocystidia ( Boekhout 1990). Moreover, the phylogenetic analyses of the combined nrITS and nrLSU sequences demonstrate the independent position of these three species on the tree ( Fig. 1 ).

The macromorphology of V. orientalis makes it also close to V. diplasia (Berk. & Broome 1871: 151) Singer (1949: 401) , edible mushroom species currently cultivated in both tropical and subtropical regions. The main differences between the two species are colour of the volva, shape and size of basidiospores and cheilocystidia. The volva of V. diplasia is more light coloured, while V. orientalis has dark brown volva with distinct olive tint; the spores of V. diplasia are more elongate, often subcylindrical and frequently 10 µm or longer, and cheilocystidia are piriform or clavate and significantly smaller (33–50 × 18–26 µm) (Pegler 1987) than ones in V. orientalis .

Figures

FIGURE 1.—Best tree from the ML analysis of the nrITS-nrLSU dataset for Volvariella species, with Cantharocybe gruberi as outgroup. Bootstrap support values and Posterior probability (BS/PP) are given above the branches.All tips are labelled with taxon name and voucher or strain numbers. For taxon in bold the sequences are generated in present study.

FIGURE 2.—Morphologicalfeatures ofVolvariellaorientalis. A.Mature basidiocarp.B.Terminal elementsof pileipellis.C.Pleurocystidia. D. Cheilocystidia. E. Caulocystidia. F. Basidia and spores. All from holotype (LE 313654). Scale bars: = 1 cm (for A), = 10 μm (for B), = 10 μm (for C–E) and = 10 μm (for F).