Cortinarius epsomiensis P. D. Orton, Naturalist

Cortinarius epsomiensis P.D. Orton, Naturalist, Leeds (Suppl.): 147. 1958. Figs 2G, 6F, 7F. Synonym: Cortinarius pastoralis Soop et al., Mycol. Progr. 15: 914. 2016. Pileus 25–70 mm diam., hemispherical when young, later convex to plane, with a broadly umbonate at the centre, margin becoming ± wavy, surface somewhat viscid when moist, not hygrophanous, innately fibrillose, greyish white when young, then yellowish brown to slightly ochraceous brown, with some dark striates radially, yellowing from the centre. Lamellae emarginate, moderately crowded, greyish violet when young, then greyish brown, edges paler, uneven. Stipe 55–77 mm long, 8–10 mm thick, cylindrical, slightly thickened at the base, surface whitish fibrillose, bluish tinges at the stipe apex, basal mycelium whitish. Universal veil sparse, white at first, then yellowish. Context fleshy, white, with bluish tinges at the stipe apex, later yellowish brown at base, sometimes hollow in the stipe. Odour indistinct to somewhat radish. Taste mild. Basidiospores 7.3–9.7 × 6.3– 7.7 μm, Q = 1.04–1.38, Xav. = 8.4–8.6 × 6.9–7.2 μm, Qav. = 1.18–1.24, subgloboid to broadly ellipsoid, moderately to rather strongly and densely verrucose, indextrinoid. Basidia clavate, 4-spored, hyaline to subhyaline, rarely yellowish to yellowish brown. Lamellar edge fertile. Pileipellis duplex: epicutis well developed, hyphae loosely interwoven, hyaline to slightly yellowish brown, 3.0–7.7 μm wide, smooth to slightly encrusted; hypocutis well developed, hyphae 8.7– 17.4 μm wide, almost hyaline, somewhat cellular, smooth. Clamp connections present. Ecology and distribution: Scattered or gregarious, associated with Betula in Northeast China. Widespread in Europe as well, associated with several deciduous trees and with Helianthemum. Specimens examined: China, Beijing Municipality, Fangshan District, Baihuashan National Nature Reserve, in Betula albosinensis forest, alt. 1954 m, 21 Aug. 2020, T.Z. Wei, HMAS 291465, HMAS 291466; Hebei Province, Laiyuan County, Baishishan Geopark, alt. 1931 m, 25 Aug. 2020, X.N. Shan, HMAS 291356; Heilongjiang Province, Mohe County, Gulian Forest Farm, in Betula platyphylla forest, alt. 550 m, 25 Aug. 2016, M.L. Xie, HMJAU 44241, HMJAU 44242; Inner Mongolia Autonomous Region, Hexigten Qi, Huanggangliang, in Betula platyphylla forest, alt. 1743 m, 3 Sep. 2018, T.Z. Wei, Z.W. Peng, J.Y. Zhuang & T.Z. Liu, HMAS 279963; Arxan County, in Betula platyphylla forest, alt. 1200 m, 22 Aug. 2018, M.L. Xie, HMJAU 44505. Notes: Cortinarius epsomiensis is an ochraceous to brown and slender species. It occurs in broadleaf forests in northern China, especially associated with Betula. This species was reported as C. pastoralis in China (Xie 2018, Wei & Liu 2019). It is also associated with Helianthemum, Corylus, and Tilia in Europe (Dima et al. 2016, Liimatainen & Ainsworth 2018). Phylogenetically, the sister species of C. epsomiensis is Cortinarius sp 14 from which it differs by six substitutions and indel positions in nrITS region, with a similarity of 99.0 %.