Cortinarius subalbocyaneus M. L. Xie, T. Z. Wei, Y. Li & Dima 2025, sp. nov.

Cortinarius subalbocyaneus M.L. Xie, T.Z. Wei, Y. Li & Dima, sp. nov. MB 843753. Figs 4E, 4F, 6O, 7O. Etymology: The name refers to the affinity to Cortinarius albocyaneus. Typus: China, Inner Mongolia Autonomous Region, Eerguna County, Moerdaoga Town, in mixed forest of Betula platyphylla and Larix gmelinii, alt. 750 m, 24 Aug. 2018, M.L. Xie (holotype HMJAU 48659). Pileus 23–34 mm diam., convex when young, later plane to convex, surface somewhat viscid when young, somewhat shiny to distinctly glittery when dry, not hygrophanous, with greyish fibrillose, at first violet grey, then slightly brownish orange, paler at the margin. Lamellae emarginate, moderately crowded, greyish violet when young, finally greyish orange to brown, edges somewhat uneven. Stipe 72–102 mm long, 3–5 mm thick above, cylindrical to subcylindrical, somewhat thickened at the base (up to 9–17 mm), surface with shiny greyish white fibrillose, white when young, blue tinges at the apex, finally dull whitish to yellowish. Universal veil greyish, forming fibrils on pileus surface and a sock like sheath on the stipe, later sparse, sometimes discolouring yellowish. Context fleshy, marbled watery when young, somewhat hollow in stipe, at first whitish, bluish tinges at the stipe apex. Odour somewhat radish. Taste mild. Basidiospores 7.7–9.7 × 6.2– 7.7 μm, Q = 1.04–1.48, Xav. = 7.9–8.6 × 6.7–7.0 μm, Qav. = 1.14–1.29, subgloboid to broadly ellipsoid, rarely ellipsoid, moderately to rather strongly and densely verrucose. Basidia clavate, 4-spored, hyaline to subhyaline, rarely yellowish to yellowish brown. Lamellar edge fertile. Pileipellis duplex: epicutis thinly developed, hyphae parallel, yellowish to slightly yellowish brown, 4–8 μm wide, smooth; hypocutis well developed, hyphae 10–19 μm, hyaline, somewhat cellular. Clamp connections present. Ecology and distribution: Solitary or gregarious in Betula platyphylla or mixed with Larix gmelinii, also associated with Populus based on the sequences of ECM root sample. Known from Heilongjiang and Jilin of China, as well as Canada, Estonia and Amur Oblast of Russia based on molecular data. Additional specimens examined: China, Heilongjiang Province, Tahe County, Tafeng Forest Farm, in mixed forest of Betula platyphylla and Larix gmelinii, alt. 360 m, 28 Aug. 2016, M.L. Xie, HMJAU 44282; Jilin Province, Antu County, Changbai Mountain National Nature Reserve, in Betula platyphylla forest with scattered Populus, alt. 1100 m, 6 Sep. 2018, M.L. Xie, HMJAU 48660, HMJAU 48661; under Betula platyphylla trees, alt. 1110 m, 19 Sep. 2020, M.L. Xie, HMJAU 48728, HMJAU 48729, HMJAU 48730, HMJAU 48731, HMJAU 48732, HMJAU 48733; Xizang Autonomous Region, Linzhi City, Lulang Town, Sejila Mountain, in Abies dominated forest with Rhododendron, alt. 3326 m, 6 Sep. 2014, T.Z. Wei, J.Y. Zhang, X.Y. Liu & H. Huang, HMAS 271932. Additional nrITS sequences data from public sequence repositories: Canada, British Columbia, FJ157104, F18506 as C. aff. caninus in GenBank; British Columbia, Cariboo, UDB031695, 228A as Cortinarius sp. in UNITE. Estonia, UDB0706856, HB29 as Cortinarius sp. in UNITE. Russia, Amur Oblast, Zeya, LC547581, szYM140 from ectomycorrhizal root tip of Populus sp., as uncultured Cortinarius in GenBank. Notes: Cortinarius subalbocyaneus is a small species. The pileus is violet grey when young, ± viscid when moist, and somewhat shiny to distinctly glittery when dry. The universal veil is greyish. The basidiospores are subgloboid to broadly ellipsoid, rarely ellipsoid. Cortinarius subalbocyaneus shows a high degree of morphological convergence with C. microalbocyaneus. However, the basidiospores of C. microalbocyaneus are rather small, on average 6.8–7.5 × 5.8–6.2 μm, and its habitats are related to Quercus mongolica. Phylogenetically, the most closely related species of C. subalbocyaneus is C. jonimitchelliae from which it differs by at least six substitutions and indel positions in the nrITS region, with a similarity of 98.9 %. The nrITS sequences FJ157104 and UDB031695 from Canada, UDB0706856 from Estonia, and LC547581 from Russia are clustered with Chinese sequences and considered as C. subalbocyaneus. This species was treated as Cortinarius sp. in Dima et al. (2021).