Caloboletus marshii, commonly known as Ben's bitter bolete,[2][3] is a species of mushroom in the family Boletaceae.

[3] The pore surface and the flesh are yellow, and quickly turn blue when bruised or cut.

[3] It can also be confused with the white king bolete, Boletus barrowsii, which doesn't bruise blue as much as Caloboletus marshii.

[3][5] Caloboletus marshii is a mycorrhizal fungus that grows under live oaks in California,[2][4] Oregon, and Washington.

However, this didn't stop a man named Ben Marsh from repeatedly trying to make it edible.