Royal Bolete

The caps are convex or flat, reaching a diameter of 6–20 cm (2+1⁄4–7+3⁄4 in) wide. The cap surface is pink to red, occasionally with hints of yellow or brown, more so around the margin. Initially velvety to slightly tomentose (hairy) when young, these minute hairs tend to slough off with age, and the cap develops wrinkles and pits. The cap flesh is yellow, usually slowly and erratically bruising blue in North American specimens. In Europe, it does not stain when exposed to air or stains weakly. The pores on the underside of the cap are angular and measure about 1–2 per millimetre. The color of the pore surface is bright yellow to start, but eventually darkens somewhat, and will stain blue with damage. The depth of the tubes comprising the pores extends to 0.8–2.5 cm (1⁄4–1 in). The stem measures 5–14 cm (2–5+1⁄2 in) long and 2.5–6 cm (1–2+1⁄4 in) thick, typically with a thick, bulbous base. It is solid (i.e., not hollow), and a bright yellow color, often with reddish tones, particularly near the base of the stem. The stem surface can be covered with fine yellow reticulations either throughout its length, or just on the upper portion. The spore print is olive-brown. …

Butyriboletus regius is an ectomycorrhizal species with a broad host range, associating with oak and conifers, especially fir. The fruit bodies grow singly, scattered, or grouped together. In North America, they usually appear from August to November, although they also appear between May and June. The North American distribution includes the Pacific Northwest states of California, Oregon, and Washington, where its frequency of occurrence ranges from "rare to locally abundant". It is rare in Europe, appearing on the Regional Red List of several countries and being considered endangered in the Czech Republic. The species has also been recorded from China.

Both European and California species are considered choice edibles, but the latter can be maggot-infested.