Today’s entry on Agaricus deardorffensis (originally posted as Agaricus praeclaresquamosus, but updated in 2018 to reflect the new understanding) is also partially written by the submitting photographer.
leafdesigner@UBC Botanical Garden Forums 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, [this species] 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 deardorffensis 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!).