This mushroom with the mouthful of a scientific name is sometimes called the "western flat-top Agaricus." A member of the same genus as the cultivated or "button" mushroom, it is poisonous. The odor of crushed flesh is disagreeable, being described as "creosote-like" or "smelling of library paste." A good field mark is the bright yellow staining that occurs when the base of the stem is nicked, although this also happens with the equally poisonous A. xanthodermus. Photographed at the Hoyt Arboretum in Portland, Oregon.