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

Cortinarius albocyaneoides M.L. Xie, T.Z. Wei & Y. Li, sp. nov. MB 843745. Figs 2A, 6A, 7A. Etymology: The name refers to morphological similarity with Cortinarius albocyaneus. Typus: China, Inner Mongolia Autonomous Region, Genhe County, Mangui Town, in mixed forest of Larix gmelinii and Betula platyphylla, alt. 630 m, 24 Aug. 2017, M.L. Xie (holotype HMJAU 48664). Pileus 16–64 mm diam., at first convex, later plane to plano-convex, margin persistently incurved, becoming ± wavy, surface somewhat viscid and weakly hygrophanous when moist, somewhat wrinkled, at first with some greyish white universal veil, especially at the margin, smooth when mature, greyish lilac to dull violet grey when young, then slightly greyish ochraceous to greyish brown, with violet tinge. Lamellae subadnate at first, then emarginate, moderately crowded, greyish violet when young, later greyish ochraceous to brown, edges somewhat paler, even. Stipe 50–95 mm long, 6–10 mm thick, cylindrical to subcylindical, slightly thickened at the base, surface shiny white fibrillose, violet tinged when young, later dull whitish to yellowish. Universal veil whitish to greyish white, forming fibrils on pileus surface and sock like sheath on the stipe when young, later becoming yellowish. Context fleshy, hygrophanous when moist, soft, becoming hollow, at first greyish violet at the pileus and upper part of stipe, yellowish below, becoming yellowish in age. Odour indistinct. Taste mild. Basidiospores (6.9–)7.3–8.7 × 5.8–6.8 μm, Q = 1.11–1.34, Xav. = 7.6–7.9 × 6.2–6.5 μm, Qav. = 1.20–1.25, subgloboid to broadly ellipsoid, moderately verrucose. Basidia clavate, 4-spored, hyaline to subhyaline, rarely yellowish to yellowish brown. Lamellar edge fertile. Pileipellis duplex: epicutis well developed, hyphae loosely interwoven, hyaline or yellowish to yellowish brown, 2–10.5 μm wide, smooth; hypocutis well developed, hyphae 10–22 μm wide, hyaline or slightly yellowish brown, somewhat cellular, smooth. Clamp connections present. Ecology and distribution: Solitary or gregarious in mixed forests of Larix gmelinii and Betula platyphylla. Known from Northeast China, as well as from Japan based on molecular data. Additional specimens examined: China, Inner Mongolia Autonomous Region, Genhe County, Mangui Town, in mixed forest of Larix gmelinii and Betula platyphylla, alt. 630 m, 24 Aug. 2017, M.L. Xie, HMJAU 48637, HMJAU 48663; Genhe County, Mangui Town, Ningcuishan Park, in mixed forests of Larix gmelinii and Betula platyphylla, alt. 820 m, 25 Aug. 2017, M.L. Xie, HMJAU 48665 Additional nrITS sequences data from public sequence repositories: Japan, Yamanashi, Mount Fuji, AB848433, YM580 from root tip, as uncultured Cortinarius in GenBank; Morioka, Pinus densiflora, AB251830, Pdmt24 as uncultured ectomycorrhizal fungus in GenBank; Hokkaido, Abies sachalinensis, LC711478, a317_GR1_ma_td_4_1_ sirokoke2_e192_TD from root tip, as uncultured fungus in GenBank, LC711479, a207_GR1_chi7_1_ sirokoke1 from root tip, as uncultured fungus in GenBank, LC711480, a302_ GR1_chi3_2_sirokoke2 from root tip, as uncultured fungus; LC711481, a102_PC1_chi7_2_sirokoke from root tip, as uncultured fungus in GenBank. Notes: Cortinarius albocyaneoides produces small- to medium-sized basidiomata, a greyish violet to greyish brown pileus, and subgloboid to broadly ellipsoid basidiospores. The Chinese specimens occur in mixed forests of Larix gmelinii and Betula platyphylla. Moreover, based on the root data from Japan, this species also occurs with Pinus and Abies. Its appearance is similar to that of C. albocyaneus and C. epsomiensis. However, the basidiospores of C. albocyaneus and C. epsomiensis are rather large, on average 8.5–9 × 6–7.5 μm and 8.5–9 × 7–8 μm, respectively (Dima et al. 2016). The nrITS sequences of all Chinese specimens are identical and the holotype differs from other known members of sect. Anomali by at least 17 substitutions and indel positions. Six nrITS sequences in GenBank that originated from Japan, AB848433 from an ectomycorrhizal root tip in the Fuji Mountains, AB251830 from an uncultured specimen in Morioka and LC711478–LC711481 from ectomycorrhizal root tips of Abies sachalinensis in Hokkaido, are clustered with Chinese collections and considered as C. albocyaneoides.