Cortinarius quercoflocculosus Kałucka & Liimat., sp. nov.

Index Fungorum number: IF 558554; MycoBank number: MB 558554; Facesoffungi number: FoF 09968; Fig. 1

Etymology – The name refers to the association of the species with oak (Quercus) as well as flocculose cap and stipe.

Holotype – LOD(F):47002

Pileus 2–4 cm in diam., convex, not umbonate or with obtuse umbo, later broadly truncate or even with a shallow depression in the centre, with margin incurved downwards, finely fibrillose to sparsely flocculose, especially towards the margin, rusty medium brown, cinnamon brown, honey brown, beige brownish, ochraceous, frequently with darkercentre; hygrophanous, margin striate, paler. Lamellae distant, adnate, rusty brown, bluish brown when young, with paler edge. Stipe 3.5–7 cm long, 0.4–0.8 cm thick at apex, 0.5–1 cm thick at the base, cylindric or frequently slightly wider at the base, solitary or cespitose, whitish silky fibrillose to sparsely flocculose, greyish white, light brownish, with bluish/lilac or rosy tinge (usually present more at the
apex, but sometimes visible only at the base). Context: not checked. Universal veil white, fibrous to floccose, abundant. Odour in lamellae indistinct or of cedar wood. Basidiospores (8–)8.5–9.5(–10) × 5–6 µm, av.=9 × 5.5 µm, Q =1.5–2, Qav.=1.5, ellipsoid to somewhat amygdaloid, moderately verrucose, moderately to fairly strongly dextrinoid, ochre brown in 10% KOH, spore deposit relatively bright, light rusty brown. Basidia 26–32×8–9 µm, narrowly clavate, with four sterigmata. In KOH, some basidia with dark brown amorphous pigment. Lamellar trama hyphae weakly pigmented, light yellowish ochre, smooth, with infrequent fine granular or spot-like encrustations. Pileipellis: Epicutis very thin, of 2–3 layers of parallel hyphae 4–10 µm, av.=6.5 µm, smooth, with cementing yellow parietal pigment, with a few ascending, slightly inflated hyphae with ends 8–17 µm, av.=12.7 µm. Hypoderm elements pale, consisting of 5–6 rows of±parallel subcellular elements, 28–57(78)×14–25 µm, av.=41.5×19 µm, hyaline with yellowish cementing parietal pigment. Trama yellowish, consisting of parallel hyphae, 7–15(19) µm wide, av.=11 µm, in the upper part tightly cemented with yellowish parietal pigment, with infrequent, scattered spot-like encrustations, parietal streaks and lumps of amber-like pigment, gradually transitioning to the more loose layer of subcellular elements, 42–74×16–24 µm, av.=20×57 µm, with very few fine spotlike encrustations. Oleiferous hyphae present. ITS sequence (GenBank MZ648198, holotype) different from the most similar sequence available in GenBank (FJ946918; Spain, Quercus ectomycorrhizal root) with only 1 substitution so probably represents the same species. C. quercoflocculosus is distinct from the closest known species, C. fulvopaludosus, and deviating with 12–14 substitutions and indels.

Ecology and distribution – In European oak forests, growing in groups of sporocarps and frequently cespitose; basidiomata found in October and November. Material examined: POLAND, Mt Kamieńsk lignite mine spoil heap near Bełchatów, young Quercus robur plantation with some solitary Betula pendula and Pinus sylvestris, on slightly acid to slightly alkaline clay, 1.17–5.96% CaCO3, 12 November 2011, leg. I.L. Kałucka 00260 (LOD(F):47002, holotype; K, isotype); loc. cit., 2 October 2013, leg. I.L. Kałucka 00270 (LOD(F):47003); Adamów lignite mine spoil heap near Turek, in Q. robur stand, 10 October 2012, leg. I.L. Kałucka 00523 (LOD(F):47004).

GenBank number – LOD(F):47002: ITS = MZ648198; LOD(F):47003: ITS = MZ648199; LOD(F):47004: ITS=MZ648200.

Notes – The two collections from Mt Kamieńsk, which is the outer spoil heap of the Bełchatów opencast lignite mine, including the holotype, come from the same young oak stand; the third Polish collection was found in oak stand on a lignite mine spoil heap Adamów, 110 km apart (Kałucka et al. 2016). The ITS region of this species seems to match a single sequence known from a Quercus ectomycorrhizal root from Spain. Thus, the species is expected to occur at least throughout the oak forests of Europe. The closest known species, Cortinarius fulvopaludosus, differs in having acute umbo, slenderer stipe with very sparse veil fibrils, with a lack of blueish tinge in lamellae and stipe and narrower spores (Fig. 1). In our phylogenetic analysis, Cortinarius quercoflocculosus formed a well-supported clade (100% MLBS; Fig. 2) within other telamonioid ITS sequences and based on the molecular and morphological data, the taxon is described here as new.

Figure 1 – Cortinarius quercoflocculosus (LOD(F):47002, holotype). a Basidiomata. b Basidiospores. c Oleiferous hypha in trama. d Pileipellis structure. Scale bars: a=20 mm, b=10 µm, c, d=20 µm

Figure 2 – Phylogram resulting from the RAxML (Stamatakis 2014) analysis of ITS region. Bootstrap values equal to or greater than 50% are indicated above the nodes. The specimens in boldface represent the type specimens of the species. The newly generated sequences are in blue