Suillus sibiricus Singer, Farlowia 1945

Suillus sibiricus (Singer) Singer, Farlowia 2 (2): 260 (1945) (Fig. 3 e, f)

Pileus 30–100 mm in diam., rounded convex, convex to expended, sometimes umbonate, viscid, light-yellow, brownyellow, with separate clear reddish-brown fibrous scales or spots, margin often appendiculate with soft white-yellow patches of veil tissue. Hymenophore as tubes, adnate or slightly decurrent, yellow, turning brown-yellow. Pores are angular, stretched in radial dimension, 1–2 mm in diam.. The young specimens with fibrous, white-yellowish partial veil, leaving more or less visible ring on the stipe. Stipe 50–110 × 5–15 mm, cylindrical, pale-yellow, covered by lightbrown, yellow-brown glandular dots, which turn brown-red when damaged or touched.

Basidia 20–30 × 6–8 μm, narrow-clavate, 4-spores. Basidiospores (8.5)9–11(13) × 4–5 μm, Q = 2.1–2.5, fusiform, yellowish. Cystidia (cheilo-, pleuro- and caulocystidia) 35–73 × 6–9 μm, clavate or fusiform, hyaline or with brown or dark-brown content, fasciculate, surrounded with brown amorphous pigment at the base. Pileipellis consisting of intertwined gelatinous hyphae of 3–8 μm in diameter.

Ecology and distribution. The species is widespread and form ectomycorrhizae with pines: in Europe (Alps, Tatras)—with Pinus cembra, P. peuce Griseb. (1846: 349) and P. strobus; in China —with P. armandii Franch. (1884: 285) and P. koraiensis; in North America—with P. monticola Douglas ex D. Don in Lambert (1832: 144) and P. flexilis (Munoz 2005; Wu et al. 2000). In Russia, Suillus sibiricus is wide spread in Siberia and Far East, rarely found in Northern Urals in forests with Pinus sibirica (Nezdojminogo 1969; Vassiljeva 1973; Petrov 1991; Perova & Gorbunova 2001; Perevedentseva 2008; Sazanova 2009; Gorbunova & Stepantsova 2015; Filippova & Bulyonkova 2017; Degteva 2019).

Collection examined. RUSSIA, Troitsko-Pechorsky district, Pechoro-Ilychsky Nature Reserve, the settlement Yaksha, 61°49’18.6”N, 56°50’21.4”E, inside the settlement, near the tree of Pinus sibirica, 15 Jul. 2015, col. A. Bobretsov, SYKOf 2663; 6 km upstream the Pechora River from cordon Shezhym-Pechorsky, 62°03’39.2”N, 58°28’4.1”E, spruce green moss forest with Pinus sibirica and Abies sibirica, 31 Jul. 2015, col. A. Bobretsov, SYKOf 2668; place Log Iordanskogo, near the Medvezhya Cave, 62°00’42.8”N, 58°38’51.2”E, birch-spruce herb forest with Pinus sibirica, 18 Aug. 2003, col. M. Palamarchuk, SYKOf 2877. Vuktyl district, “Yugyd va” National Park, basin of the Schugor River, Nizhnie Vorota, right bank, lower course of the river Kyrtael, 64°13’12.1”N, 57°58’35.4”E, spruce herb forest with Pinus sibirica, 11 Aug. 2016, col. M. Palamarchuk, SYKOf 2521.

Note. The most similar species (S. acidus var. intermedius), is distinguished by the absence of clear scales on the pileus, the presence of black glandular dots and a distinct ring on the stipe.