Boletus regius, the regal or butter bolete, is a basidiomycete

Basidiomycota

Basidiomycota is one of two large phyla that, together with the Ascomycota, comprise the subkingdom Dikarya within the Kingdom Fungi...

 fungus

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 of the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Boletus

Boletus

Boletus is a genus of mushroom, comprising over 100 species. The genus Boletus was originally broadly defined and described by Elias Magnus Fries in 1821, essentially containing all fungi with pores...

found in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. B. regius has a pink cap, yellow flesh, and a reticulate pattern on the stem. Harry D. Thiers

Harry D. Thiers

Harry Delbert Thiers, born January 22, 1919 in Fort McKavett, Texas, died August 8, 2000 in Ohio, was an American mycologist who studied and named a great many fungi of native to North America, particularly California. Thiers taught mycology at San Francisco State University for many years, and a...

 described a similar mushroom from California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

as B. regius, although it has yet to be shown to be the same species. B. regius in Europe does not stain when exposed to air, but the California species stains blue. Both European and California specimens are considered choice edibles.