Cap 7-14 cm broad, convex, expanding to nearly plane, the disc sometimes slightly depressed; margin at first incurved, then decurved, occasionally wavy; surface dry to subviscid depending on conditions, glabrous to minutely tomentose; color variable: cream-yellow, buff-brown to yellow-brown, often flushed with rusty to reddish-brown tints in age, darkening where handled; context 1.5-3.0 cm thick, firm, cream to pale-yellow, unchanging or bluing erratically; odor and taste mild.
Pores minute when young, up to 1 mm broad at maturity, angular, not boletinoid, at first pale-yellow, then lemon-yellow, eventually dull olive-yellow, bruising blue; tubes 1-1.5 cm long, colored like the pores, depressed at the stipe.
Stipe 5-9 cm long, 3-6 cm thick at the thickest point, typically clavate to bulbous, occasionally equal, the base sometimes narrowed to a point; surface of upper-half reticulate, glabrous below, cream-yellow to yellow, frequently overlain with reddish tints, bruising brown where handled; veil absent.
Spores 11.5-13.5 x 3.5-4.5 µm, subfusoid, smooth, thin-walled; spore print olive-brown.
Solitary to scattered under hardwoods, particularly oaks (Quercus spp.) and tanbark oak (Lithocarpus densiflora); fruiting shortly after the fall rains.
Edible and choice.
Boletus appendiculatus is distinguished by a cream to yellow-brown cap often suffused with rusty-brown to reddish-brown tints, yellowish pores that readily blue and a hardwood habitat. Its robust stature and reticulate stipe sometimes cause confusion with three other local boletes: Boletus regius, B. edulis and B. aereus. Boletus regius is similar but has a pinkish-red cap which becomes paler in age and does not develop rusty-brown to reddish-brown tints. Boletus edulis, the King Bolete, also has a differently colored cap: buff, tan-brown to chestnut-brown, pale pores when young which never bruise blue, and is found mostly with pines. Boletus aereus, the Queen Bolete is an occasionally encountered bolete that is associated with hardwoods. It has a dark-brown to almost blackish cap when young, a more or less equal stipe at maturity, and like Boletus edulis, does not bruise blue. All of these species have a mild taste and are edible. Boletus appendiculatus is considered by some to be superior to B. edulis because of a firmer texture. Unfortunately it is seldom found in quantity.