Rugiboletus extremiorientalis (Lj.N. Vassiljeva) G.Wu & Zhu L. Yang 2015, in Wu et al. Fungal Diversity 81(1):1–24 (2015)
Pileus 8–11 cm in diam., hemispherical to broadly convex, subtomentose, brownish yellow, yellowish brown to brown (5C8–5E8), often viscid when wet, incurved or suspended at the margin, usually wrinkled when young and crackled when old; context pale yellow to light yellow (2A2–2A4), ca. 2 cm thick, unchanging when bruised. Hymenophore adnexed; surface cream yellow, light yellow (3A7–3A8), almost concolorous with tubes, unchanging when bruised; pores nearly round, minute, ca. 2.5/mm, unchanging when bruised; tubes grayish yellowish (2B3–2B4), 1.5–2 cm long, free, unchanging when bruised. Stipe 9×2 cm, cylindrical to subcylindrical, light yellow to canary yellow (2A5–2B8), with concolorous or darker (brownish yellow) dotted squamules on the stipe, sometimes streaked with fibrils at the lower part; context pale yellow to light yellow (2A2–2A4) mixed with brown tinge, unchanging when bruised; basal mycelia off-white. Macrochemical reaction not observed.
Basidia 21–36×8.5–14 μm, clavate to broadly clavate, 4- spored, sometimes 1 or 2-spored. Basidiospores 11–13×4–5 (5.5) μm, [Q=(2.18) 2.45–3.17 (3.25), Qm=2.81±0.19], subfusoid and inequilateral in side view with distinct suprahilar depression, narrow subfusiform to elongated oviform in ventral view, light yellow, smooth, inamyloid. Hymenophoral trama boletoid, hyphae cylindrical, 4–8 μmwide. Cheilocystidia 22– 35×5–8 μm, fusoid-ventricose to subfusoid-mucronate with subacute apex, or clavate, thin walled. Pleurocystidia 20–60× 7–13 μm, broadly fusoid-ventricose to ventricose, sometimes with subacute apex, thin walled. Pileipellis an ixotrichodermium to an interwoven ixotrichodermium composed of brown to yellowish brown branched filamentous hyphae 3–6 μm in width with terminal cells 26–64×3–11 μm, which are almost subcylindrical with subacute apex to cystidioid, rarely inflated. Pileal trama composed of interwoven hyphae 3–6 μm wide. Stipitipellis hymeniform, 60–90 thick, composed of more or less vertically light brown to yellowish brown hyphae, terminal cells 20–40×8–16 μm. Stipe trama composed of slightly thick-walled (<1 μm) parallel hyphae 5–10 μm wide. Clamp connections absent.
Habitat: solitary or scattered, inmixed forests of Pinus spp. (P. yunnanensis and P. densiflora, etc.) and Fagaceae (Quercus spp., Castanopsis spp., and Lithocarpus spp.) or the forests dominated by Fagaceae.
Known distribution: China: Currently known from southwestern, central, and northeastern China (Li and Bau 2003); Far East Russia (Vassiljeva 1950); Korea (Kim et al. 1975); Japan (Hongo and Izawa 1994); Nepal (Christensen 2009); Thailand (Chantorn et al. 2007).
Index Fungorum number: IF 810363
Notes: Rugiboletus extremiorientalis was originally considered as a Krombholzia, and then transferred to Leccinum Gray sect. Luteoscabra Singer by Singer (1962). Binder and Besl (2000) and Zang (2013) also treated it in Leccinum. However, it never stains brown when bruised or cut, a feature that could be used to distinguish this genus from Leccinum species.
Figure 1: Basidiomata of Rugiboletus extremiorientalis (m HKAS 74770, n HKAS 63523) Scale bars =5 cm