Pleuromyces fauriei Svetash., E.F. Malysheva & S.N. Bondarchuk, 2025

Malysheva, Ekaterina F., Svetasheva, Tatiana Yu. & Bondarchuk, Svetlana N., 2025, Towards a taxonomy of Pleuromyces (Agaricomycetes): a new species of P. fauriei from Russia described and the status of the genus within the Agaricales reconsidered, Phytotaxa 705 (1), pp. 63-74 : 68-70

Pleuromyces fauriei Svetash., E.F. Malysheva & S.N. Bondarchuk , sp. nov. ( Figs. 3 and 4 )

MycoBank: MB858489

Diagnosis:—Basidiomata pleurotoid, not stipitate, very small, up to 3 mm in diameter, slightly felted, pale colored, mainly whitish, growing in large colonies. The spores are ovoid to ellipsoid, somewhat angular, (6.1)7–7.8(8.2) × (4.1)4.4–5.6(6) μm, cheilocystidia distinctly capitate.

Holotype:— RUSSIA. Primorsky Krai, Sikhote-Alin Nature Reserve, “Kabaniy” field station, permanent plot “Fori 1”, 45°07’22.8” N 135°51’34.8” E, forest site dominated by Rhododendron fauriei , with Pinus koraiensis , Abies , Betula , Picea , Acer and other trees, on fallen branches of Rhododendron fauriei , 14 Aug. 2024, T. Yu. Svetasheva (LE F-354615). GenBank nrITS: PV394772, nrLSU: PV394774.

Etymology:—The name refers to the substrate of Rhododendron fauriei branches on which the species was collected.

Description:—Basidiomata pleurotoid or crepidotoid without a stipe, dorsally or laterally attached. Pileus tiny, 0.7–3.0 mm diam, cup-shaped to fan-shaped with incurved to straight, slightly wavy margin; whitish (Wool white RAL 060 93 05 or Grain white RAL 060 90 05), sometimes become a bit brownish (Apricot brown RAL 050 60 40) with age; surface dry, felted, somewhat rugulose, not hygrophanous. Lamellae ventricose, with lamellulae, pale yellowish or beige (Vanilla white RAL 075 93 05, Cream white RAL 090 93 05) when young, pinkish or ochre brown (Sienna ochre RAL 050 70 30, Apricot brown RAL 050 60 40 or Elm brown red RAL 060 50 60) with age or on dry specimens, edge irregular. Spore deposit ochre to reddish brown (Elm brown red RAL 060 50 60).

Basidiospores (6.1)7–7.8(8.2) × (4.1)4.4–5.6(6) μm, mean 7.4 × 5.1 μm, Q = (1.3)1.35–1.6(1.8), Q av = 1.5, ovoid to ellipsoid, slightly irregular or uncertainly angular in side view, smooth, unevenly thick-walled, yellowish brown, usually with one rarer two-three guttules, apex blunt, with indistinct or small germ-pore. Basidia 20–22 × 7.7–9.2 μm (excluding sterigma), subclavate, 1, 2- or 4-spored. Cheilocystidia 23.0–37.5 × 4.8–9.4 μm, abundant, in clusters on lamella edge, elongated, quite variable in shape, often lageniform with capitate apex, with a head 3.9–7.3 × 3.7–6.0 μm ending by 1–3 apical appendages, not incrusted, thin- or slightly thick-walled, predominantly hyaline, but sometimes with yellowish brown content. Pleurocystidia not observed. Hymenophoral trama regular. Pileipellis a trichocutis, scarcely incrusted, composed of flexuous thick-walled pigmented hyphae 3–4 μm wide, terminal elements, 25.5–39.5 × 3.0–4.5 µm, cylindrical with sinuous walls, usually with rounded apex, thick-walled, brownish. Subpellis made of cylindrical hyphae 3–4 μm wide, pale to yellowish brown, smooth, distinctly thick-walled and clamped at every septa.

Habitat and distribution:—On branches of Rhododendron fauriei Franch. , in the mountain relict old-growth mixed forest. So far only known from the type locality.

Additional specimen studied:— RUSSIA. Primorsky Krai, Sikhote-Alin Nature Reserve, “Kabaniy” field station, permanent plot “Fori 1”, forest site dominated by Rhododendron fauriei , with Pinus koraiensis , Abies , Betula , Picea , Acer and other trees, on fallen branches of Rhododendron fauriei , 14 Aug. 2024, S. N. Bondarchuk (LE F-354623). GenBank nrITS: PV394773, nrLSU: PV394775.

Figures

FIGURE 3. Basidiomata in situ and microscopic characters of Pleuromyces fauriei. A. Basidiomata LE F-354615 (holotype, photo by T. Svetasheva). B. Basidiomata LE F-354623 (photo by T. Svetasheva). C. Basidiospores (from holotype). D. Cheilocystidia (from holotype). Scale bars: A, B = 10 mm; C, D = 10 μm.

FIGURE 4. Microscopic features of Pleuromyces fauriei (LE F-354615, holotype). A. Basidia. B. Basidiospores. C. Terminal elements of pileipellis. D. Cheilocystidia. Scale bar = 10 μm.