Butter-foot bolete

Appearance

The cap of ''B. auripes'' has a convex shape before flattening somewhat in maturity, and attains a diameter of 4–13 cm . The cap surface is dry, with a texture ranging from finely tomentose to nearly smooth, and colored yellowish brown to chestnut brown or grayish brown. The cap color fades with age. Similarly, the flesh—initially yellow—fades to whitish in maturity. Unlike some other ''Boletus'' species, in ''B. auripes'' neither the surfaces nor the internal tissue turns blue when injured or exposed to air. The odor and taste of the mushroom are not distinctive.

Initially pale yellow to yellow, the pore surface develops olive tinges as it matures, and often becomes depressed near the stem attachment. Pores are circular to angular, and minute—typically less than 1 mm wide; the tubes are 1–2.5 cm deep. The golden-yellow stem is 7–10 cm long by 2–3 cm thick. Young stems are typically bulbous to club-shaped, but this evens out somewhat as the mushroom grows, and mature stems are club-shaped to nearly equal in width throughout. The stem is dry, solid , and features yellow reticulation, at least on the upper portion. Mycelia at the base of the stem have a buff color. The fruit body does not have a partial veil or a ring on the stem. ''Boletus auripes'' is edible.

Mushrooms produce a spore prints that is yellow brown to olive brown. The smooth, yellowish spores measure 10–14 by 3–5 μm, and range in shape from roughly elliptic to cylindric to subfusoid . The basidia are club-shaped, four-spored, and measure 27.2–35.2 by 9.6–10.4 μm. The cellular arrangement of the cap cuticle is a trichodermium consisting of erect hyphae with a diameter of 3.2–6.4 μm.

Naming

Field characteristics used to distinguish ''Boletus auripes'' from potential lookalike species include the yellowish brown to chestnut-brown cap surface that becomes paler with age, yellow flesh that does not stain blue, and a reticulate stem. ''B. aureissimus'' has a similar appearance, but has a honey-yellow to bright yellow or yellow-ochre cap, less conspicuous stem reticulation, and a more limited range covering Florida west to Texas. ''B. aureissimus'' var. ''castaneus'' has a purplish-brown cap with a texture like velvet.

''Boletus auripes'' somewhat resembles ''B. aurantiosplendens'', but the latter species has a more variably colored cap that can be orange, brownish orange, or yellowish, and variable degrees of stem reticulation. ''B. hortonii'' has a similar color scheme but lacks reticulation on the stem. ''B. auripes'' bears a superficial resemblance in coloration to the Costa Rican species ''B. lychnipes'', known only from a limited area in the northern Cordillera de Talamanca. The latter species may be distinguished by the lack of reticulations on the upper half of the stem, a brown or salmon-pink staining reaction on the stem in response to handling, and microscopically by a conspicuously sterile margin and prominent pseudocystidia. ''Retiboletus retipes'' is set apart from ''B. auripes'' by a darker cap, tubes that lack an olive tinge, and a stem that has more prominent reticulation extending down to the base. In contrast to ''B. auripes'', ''B. impolitus'' has a floccose or tomentose cap surface, and lacks an olive tinge on the tubes.

Distribution

''Boletus auripes'' is mycorrhizal, and fruits singly, scattered, or in groups on the ground under broadleaf trees, especially oak and beech, but it has also been recorded associating with mountain laurel . ''Boletus auripes'' typically forms fruit bodies between June and November.

''Boletus auripes'' has a disjunct distribution, and is one of several fungi found in both eastern Asia and eastern North America. In North America, where it is relatively common, the range of the fungus extends from Alaska south to Mexico, and east to New York. In Central America, it has been recorded in Belize. The mushroom has also been recorded from Taiwan, China , and Japan. It was reported for the first time from the Russian Far East in 2008.

Habitat

''Boletus auripes'' is mycorrhizal, and fruits singly, scattered, or in groups on the ground under broadleaf trees, especially oak and beech, but it has also been recorded associating with mountain laurel . ''Boletus auripes'' typically forms fruit bodies between June and November.

''Boletus auripes'' has a disjunct distribution, and is one of several fungi found in both eastern Asia and eastern North America. In North America, where it is relatively common, the range of the fungus extends from Alaska south to Mexico, and east to New York. In Central America, it has been recorded in Belize. The mushroom has also been recorded from Taiwan, China , and Japan. It was reported for the first time from the Russian Far East in 2008.