This photograph is courtesy of “leafdesigner” (a member of the UBC Botanical Garden Forums) of Battle Ground, Washington. leafdesigner submitted this image via the BPotD Submissions Forum here. Thanks for the image, and also thanks for writing accompanying text! leafdesigner writes:
“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 Agaricus xanthodermus.”
I'll add an additional link: Agaricus praeclaresquamosus via Mykoweb.
Botany resource link: the Fungus Identification Forum, recently separated out as its own discussion area on the garden's forums after a request from one of the forum members. Identification of fungi can be extremely challenging, often requiring the use of a microscope and “spore prints”. Unlike lichen identification, though, you don't need to walk around with a chemistry set (a story for another day). Despite often requiring lab work, identification to genus is possible for many fungi with a good image and description, like so: Hydnellum peckii (which I absolutely have to find one day for BPotD!).