Macromorphology: Pileus 3-15 cm; convex becoming broadly convex or plane; surface dry or slightly tacky, very finely tomentose or glabrous; frequently pitted or rugulose in youth and/or areolate at maturity; color variable, but frequently mustard yellow to orangish yellow young, becoming brownish yellow or brownish before fading to tan—or medium brown young, fading to yellowish brown or tan; with a tiny (1 mm) sterile margin but without substantial overhanging flaps. Context quite firm (nearly brittle when young); whitish or pale yellowish; changing to pinkish or reddish when sliced and exposed to air, then grayish to blackish over the course of 20-60 minutes (Figure 3). Tubes to 2 cm long; yellowish to greenish yellow; pore surface dull yellow to yellowish, becoming olive yellow or brownish, not bruising or bruising brownish, depressed at the stipe; 1-2 pores per mm. Stipe 4-15 cm long; 14-30 mm wide; often subclavate when young but at maturity more or less equal, or tapering to apex and/or base; yellowish or whitish (sometimes with reddish areas, especially in wet weather); finely pruinose or subreticulate apically; scabrous for about the bottom two-thirds with yellowish, medium brown, cinnamon brown, or grayish brown scabers; basal mycelium whitish to yellowish. Odor and taste not distinctive. Exsiccata with a dark reddish brown pileus surface, a dull grayish olive to dirty ochraceous pore surface, and a brownish ochraceous stipe surface adorned with concolorous or brownish scabers. Spore print brownish to olive brown.
Chemical reactions (Figure 4): KOH red on pileus surface; golden yellow to rusty or orangish on context. Ammonia reddish or negative on pileus surface; yellowish to negative on context. Iron salts grayish on pileus surface, greenish gray to olive on context.
Micromorphology: Basidiospores subfusoid; inamyloid; yellowish in KOH; smooth; (9.5-) 12-21 x (3-) 4-6 µ. Basidia clavate; four-sterigmate; up to 40 × 12 µ. Hymenial cystidia (Figure 5) fusoid-ventricose with a long neck; up to 48 × 13 µ; hyaline to yellowish in KOH; scattered to numerous. Pileipellis (Figure 5) a trichoderm of chained elements, the penultimate and/or antepenultimate (occasionally the terminal) element often swollen up to 33 µ wide; hyaline to yellowish or brownish in KOH. Caulocystidia (Figure 5) in bundles with caulobasidia; variously shaped but mostly fusoid-ventricose with a long, twisted neck; also mucronate, clavate, or irregular; up to 70 × 20 µ or longer; hyaline to yellowish brown in KOH.
Molecular Data: Two partial sequences have been deposited in GenBank: DQ407250 (partial ITS1-complete 5.8S-partial ITS2, deposited by Y. Zhao, citing a Y. Zhao collection from China in an uncited herbarium), apparently not publically aligned; and AY612813 (partial 28S, deposited by T. Y. James and collaborators with a voucher of “TH6967” in an uncited herbarium), aligned by Binder & Hibbett (2004) and by den Bakker & Noordeloos (2005). The Binder & Hibbett and den Bakker & Noordeloos alignments are similar, though not identical, placing AY612813 in a clade with oak- and hornbeam-associated taxa; in the den Bakker & Noordeloos alignment AY612813 is sister to a clade containing Leccinum subglabripes, Leccinum longicurvipes, Leccinum crocipodium, and other taxa; in the Binder & Hibbett alignment it is sister to a specimen identified as Leccinum albellum.