Crepidotus sokolovii E.F. Malysheva, 2025

Malysheva, Ekaterina & Malysheva, Vera, 2025, New species and new record of Crepidotus (Crepidotaceae, Agaricales) from Sikhote-Alin, Russia, Phytotaxa 706 (3), pp. 255-268 : 260-262

Crepidotus sokolovii E.F. Malysheva , sp. nov. ( Figs. 2 , 3 )

MycoBank: MB858726

Diagnosis:—Basidiomata small, semicircular to flabelliform, laterally attached to the substrate with pseudostipe, with even and sulcate margin; surface of pileus dry, slightly pruinose, dull ochre-brown, greyish-brown or tawny; basidiospores (5.8‒)6.7‒8.8(‒9.8) × (5.8‒)6.5‒8.2(‒9.6) µm, globose to subglobose, verrucose ornamented; cheilocystidia flexuous heteromorphic, often with apical papilla.

Holotype:— Russia. Primorsky Krai, Sikhote-Alin State Nature Biosphere Reserve, vicinity of Zimoveiny field reserve station, 45°08’20.90” N, 136°18’54.30” E, floodplain coniferous-broadleaved forest (with Pinus koraiensis and Populus maximowiczii ), on a mossy, large fallen trunk of Populus maximowiczii , 20 Aug. 2024, V. Malysheva (LE F-354604). GenBank nrITS: PV468332; nrLSU: PV468334.

Etymology:—In honor of Vladimir Sokolov, Sikhote-Alin State Nature Biosphere Reserve staff member, for his invaluable help in organising mycological research in the Reserve and many years of work on preserving the unique nature of this region.

Description:— Pileus 10‒15 mm, semicircular to flabelliform, plano-convex to applanate, laterally attached to the substrate with pseudostipe, with even and distinctly striate-sulcate margin; surface of pileus dry, not hygrophanous, slightly pruinose and tomentose along the margin and at the point of attachment to the substrate, dull ochre-brown, greyish-brown or tawny (Bamboo beige RAL 050 70 10, Amber grey RAL 050 70 20 or Medium brown RAL 050 60 30). Lamellae moderately crowded, ventricose, uniformly beige to cinnamon (Soft greige RAL 060 80 10, Peanut butter RAL 060 70 20), then spotted; lamellar edge minutely fimbriate, whitish. Stipe absent or rudimentary. Spore print yellowish brown (Camel brown RAL 060 50 40).

Basidiospores (5.8‒)6.7‒8.8(‒9.8) × (5.8‒)6.5‒8.2(‒9.6) µm (n = 100) (L av = 7.6, W av = 7.2, Q = 1.0‒1.1(1.2); Q av = 1.1), varying significantly in size even within a single basidioma, globose to subglobose, with a single, large, central oil drop, thick-walled, yellow-brown in KOH, verrucose ornamented (in light microscopy the spores appear punctate; under SEM warts irregular in shape and size, isolated or finely confluent). Basidia 27‒38 × 8‒9 µm, 2-spored, narrowly clavate. Cheilocystidia (21.6‒)24.0‒36.0(‒50.5) × (5.5‒)5.8‒9.0(‒10.0) µm, rather abundant, cylindrical, clavate, narrowly utriform, sometimes irregularly branched, with digitate projections, often apically constricted, flexuous, thin-walled. Pleurocystidia absent. Pileal trama composed of thin-walled, hyaline hyphae, 5.5–8 μm wide. Pileipellis a cutis, not-gelatinized, with tufts of erect to semi-erect undifferentiated, narrowly attenuated or filiform apical elements, up to 160 μm in length and 2.5–4 μm wide, thin-walled, hyaline. Clamps present in all tissues.

Habitat and distribution:—Solitary, on the bark of fallen, mossy trunks of Populus . Currently, only known in the Primorsky Krai, Russia.

Additional collection examined:— RUSSIA. Primorsky Krai, Sikhote-Alin State Nature Biosphere Reserve, vicinity of Zimoveiny field reserve station, 45°08’19.30” N, 136°18’33.70” E, floodplain coniferous-broadleaved forest (with Pinus koraiensis , Salix cardiophylla and Populus maximowiczii ), on fallen trunk of Populus maximowiczii , 21 Aug. 2024, E. Malysheva (LE F-354625). GenBank nrITS: PV468331.

Crepidotus indicus Manojk. & C.K. Pradeep , in Kumar, Vrinda & Pradeep, Cryptog. Mycol. 39(3): 290 (2018) ( Figs. 2 , 4 )

Pileus 10‒18 mm, semicircular to more or less flabelliform, convex when young, becoming plano-convex, some young basidiomata rather reniform, laterally attached to the substrate, with even, slightly involute margin, hygrophanous; surface of pileus dry, tomentose to pubescent, apricot to orange-pink (Mild orange RAL 060 80 30, Candle yellow RAL 060 70 40), darker on drying (Apricot brown RAL 050 60 40, Orange yellow RAL 050 60 50). Lamellae moderately crowded to distant, ventricose, uniformly beige to yellowish-brown (Ash yellow RAL 075 80 40, Apricot yellow RAL 070 80 40); lamellar edge concolorous, entire. Stipe absent or rudimentary, with white tomentum. Spore print yellowish brown (Peach yellow RAL 060 70 30).

Basidiospores (6.1‒)6.7‒7.8(‒8.6) × (5.7‒)6.5‒7.5(‒8.3) µm (n = 90) (L av = 7.2, W av = 6.9, Q = 1.0‒1.1; Q av = 1.0), globose, with a single, large, central oil drop, yellow-brown in KOH, verrucose ornamented (in light microscopy the spores appear punctate; under SEM warts conical, rounded or somewhat short-cylindrical, isolated, rarely confluent), thick-walled. Basidia 29‒44 × 6.5‒8.5 µm, 1- and 2-spored, narrowly clavate. Cheilocystidia (42.5‒)44.5‒66.5(‒75.5) × (4.5‒)5.0‒7.5(‒8.4) µm, numerous, projecting above the hymenium, forming a somewhat dense, sterile layer on lamellae margin, flexuous, cylindrical or narrowly fusiform, hyaline, thin-walled, clamped. Pleurocystidia absent. Pileal trama composed of thin-walled, hyaline hyphae, 6–8 μm wide. Pileipellis a trichoderm, composed of hyaline or yellowish, thin-walled hyphae; terminal elements (65‒)71‒126(‒135) × 4‒8 µm, cylindrical or subulate and attenuated, straight or slightly flexuous, subterminal cells often short, ventricose, 10‒15 µm wide, thick-walled and somewhat incrusted. Clamps present in all tissues.

Habitat and distribution:—In small group, on fallen, mossy trunk of Populus . Currently, known from India, North America and Asian part of Russia.

Collection examined:— RUSSIA. Primorsky Krai, Sikhote-Alin State Nature Biosphere Reserve, vicinity of Zimoveiny field reserve station, 45°08’20.90” N, 136°18’54.30” E, floodplain coniferous-broadleaved forest (with Pinus koraiensis and Populus maximowiczii ), on a mossy, large fallen trunk of Populus maximowiczii , 20 Aug. 2024, V. Malysheva (LE F-354605). GenBank nrITS: PV468333; nrLSU: PV468335.

Figures

FIGURE 2. Fresh basidiomata and SEM-micrographs of basidiospores of the studied Crepidotus species. A. Basidiomata of C. sokolovii (LE F-354604, holotype). B. Basidiomata of C. indicus (LE F-354605). C, E. Basidiospores of C. sokolovii (from holotype). D, F. Basidiospores of C. indicus. Scale bars for A–B = 1 cm.

FIGURE 3. Microscopic features of Crepidotus sokolovii (LE F-354604, holotype). A. Terminal elements of pileipellis. B. Basidia. C. Basidiospores. D. Cheilocystidia. Scale bars: A = 10 μm; B–D = 10 μm.

FIGURE 4. Microscopic features of Crepidotus indicus (LE F-354605). A. Terminal elements of pileipellis. B. Cheilocystidia. C. Basidiospores. D. Basidia. Scale bars: A = 10 μm; B–D = 10 μm.