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

Cortinarius microalbocyaneus M.L. Xie, T.Z. Wei, Y. Li & Dima, sp. nov. MB 843748. Figs 3B, C, 6I, 7I. Etymology: The name refers to the small-sized basidiomata and similarity to Cortinarius albocyaneus. Typus: China, Jilin Province: Yanji County, Sandaowan Town, Wupiyegou, under Quercus mongolica with scattered Pinus koraiensis, alt. 580 m, 4 Sep. 2019, M.L. Xie (holotype HMJAU 48706). Pileus 23–32 mm diam., convex when young, later plane, surface somewhat viscid when moist, innately fibrillose, with patches of pale yellowish universal veil remnants at the margin, sometimes wrinkle, especially at the margin when mature, at first greyish lilac to greyish violet, then greyish orange from centre. Lamellae emarginate to adnexed, moderately crowded, pale violet to greyish violet when young, later pale orange to brown, even at first, then with weakly serrate. Stipe 40–47 mm long, 6–8 mm thick, subclavate to clavate, somewhat thickened at the base, up to 11–12 mm, whitish, blue tinges at the stipe apex when young, later yellowish, basal mycelium whitish. Universal veil yellowish, sparse, sometimes forming fibrils on pileus surface and sock like sheath on the stipe. Context in pileus fleshy, hygrophanous when moist, bluish when young, especially at the stipe apex, later white, sometimes hollow in stipe. Odour radish. Taste mild. Basidiospores 6.2–7.7 × 5.4–6.8 μm, Q = 1.06–1.33, Xav. = 6.8–7.2 × 5.8–6.2 μm, Qav. = 1.17–1.20, subgloboid to broadly ellipsoid, rather weakly verrucose. Basidia clavate, 4-spored, hyaline to subhyaline, rarely yellowish to yellowish brown. Lamellar edge fertile. Pileipellis duplex: epicutis thinly developed, hyphae somewhat interwoven, hyaline or yellowish to yellowish brown, 2.5–7.5 μm wide, slightly encrusted; hypocutis well developed, hyphae 12–27 μm wide, hyaline to slightly yellowish brown, somewhat cellular, smooth. Clamp connections present. Ecology and distribution: Known from Northeast China in Betula platyphylla forests or Quercus mongolica dominated forests. It may be associated with Pinus based on the sequences (LC175062) of mycorrhizal root tips, too. Also known from Canada, Japan and USA based on molecular data. Additional specimens examined: China, Jilin Province: Yanji County, Sandaowan Town, Wupiyegou, under Quercus mongolica, with scattered Pinus koraiensis, alt. 580 m, 7 Sep. 2018, M.L. Xie, HMJAU 48649, HMJAU 48650, HMJAU 48651, HMJAU 48652; ibid., 8 Sep. 2018, M.L. Xie, HMJAU 48653; ibid., 4 Sep. 2019, M.L. Xie, HMJAU 48702, HMJAU 48703, HMJAU 48704, HMJAU 48705; ibid., 23 Sep. 2020, M.L. Xie, HMJAU 48721, HMJAU 48722, HMJAU 48723, HMJAU 48724, HMJAU 48725, HMJAU 48726, HMJAU 48727; Antu County, Changbai Mountain National Nature Reserve, under Betula platyphylla, alt. 1110 m, 19 Sep. 2020, M.L. Xie, HMJAU 48720; Ji’an County, Wunvfeng National Forest Park, unknown date, Y.L. Tuo, HMJAU 60641. Additional nrITS sequences data from public sequence repositories: Canada, British Columbia, Interior Cedar Hemlock Forests, DQ097877, OUC97234 as C. alboviolaceus in GenBank; Québec, Riviere-a-Pierre, MW845268, MQ21- HRL1598-QFB32934 as Cortinarius sp. in GenBank; Riviere-au-Tonnerre, OQ321992, MQ22-QFB33093- HRL3520 as Cortinarius sp. in GenBank. Japan, Iwate, Mt. Hayachine, LC175062, YM1162 from Pinus parviflora root tips, as Cortinarius sp. in GenBank. USA, New Hampshire, MT345185, CNV8 as Cortinarius sp. in GenBank. Notes: Cortinarius microalbocyaneus is characterized by small-sized basidiomata (pileus <50 mm diam.), greyish blue to yellowish brown pileus, clavate and somewhat hollow stipe, and subgloboid and small-sized basidiospores. Cortinarius albocyaneus and C. epsomiensis are morphologically similar species but can be distinguished by their ± shiny to distinctly glittery pileus and larger basidiospores of C. albocyaneus (8.5–9.0 × 6.0–7.5 μm) and C. epsomiensis (8.5–9 × 7–8 μm) (Dima et al. 2016, Liimatainen & Ainsworth 2018). Cortinarius microalbocyaneus also shares a similar appearance with C. albocyaneoides and C. subalbocyaneus. But C. albocyaneoides and C. subalbocyaneus have larger basidiospores and are associated with Larix and Betula. HMJAU 60641 was labeled as C. anomalus by Tuo et al. (2022), here we treat it as C. microalbocyaneus. Phylogenetically, the sister species of C. microalbocyaneus is Cortinarius sp9 from which it differs by 16 substitutions and indel positions in nrITS region, with a similarity of 97.3 %. Five GenBank sequences, DQ097877, MW845268 and OL891464 from Canada, LC175062 from Japan, and MT345185 from the USA, were treated as Cortinarius sp. in Dima et al. (2021), are clustered with the Chinese specimens and considered as C. microalbocyaneus.