Boletus Auripes
The fruit bodies (mushrooms) formed by the fungus have convex to nearly flat caps that are up to 13 cm (5.1 in) wide. The stems are up to 10 cm (3.9 in) long by 3 cm (1.2 in) thick, and feature reticulations (net-like ridges) on the upper portion. Other than the brownish upper cap, the entire surface of the mushroom is yellow. B. auripes is edible. It can be distinguished from other similar yellow boletes by differences in color, degree of stem reticulation, and distribution.
Taxonomy
The species was originally described by American mycologist Charles Horton Peck in 1898. Peck collected the type specimen in Port Jefferson, New York. In 1945, Rolf Singer proposed the variety Boletus auripes var. aureissimus as a new combination of the name Ceriomyces aureissimus described by William Alphonso Murrill in 1938; this taxon is now regarded as a distinct species under the name Boletus aureissimus. In 1936, Wally Snell reported finding a specimen of Boletus crassipes, another species described by Peck from Mount Gretna, Pennsylvania. Snell suggested that although B. crassipes might be a valid species distinguished from B. auripes by a deeper brown cap color, yellow flesh that does not fade to white, and a stem with a more orange-yellow color and more extensive reticulation, he conceded that it was not clear that the morphological characteristics between the two did not overlap, and that further collections would be needed to clarify any differences between them. A couple of years later, he was more convinced of his stance and considered the two conspecific. The taxonomic authorities Index Fungorum and MycoBank, however, do not recognize this putative synonymy.
In the genus Boletus, B. auripes is classified in section Appendiculati. Species in this section are characterized by having a dry cap with a surface texture ranging from smooth to somewhat tomentose, yellow flesh, a reticulate stem, and a mild taste. Other North American boletes in this section include Boletus speciosus and Boletus regius.
The specific epithet auripes means "golden yellow foot". It is commonly known as the "butter-foot bolete".
Description
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/20/Boletus_auripes_90459.jpg/220px-Boletus_auripes_90459.jpg)
The cap of B. auripes has a convex shape before flattening somewhat in maturity, and attains a diameter of 4–13 cm (1.6–5.1 in). The cap surface is dry, with a texture ranging from finely tomentose (hairy) 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 (0.4–1.0 in) deep. The golden-yellow stem is 7–10 cm (2.8–3.9 in) long by 2–3 cm (0.8–1.2 in) 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 (i.e., not hollow), 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 (especially in fresh prints) 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 (somewhat spindle-shaped). The basidia (spore-bearing cells) 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 (whereby the outermost hyphae emerge roughly parallel, like hairs, perpendicular to the surface of the cap) consisting of erect hyphae with a diameter of 3.2–6.4 μm.