Gills creamy yellow; taste mild; flesh not discoloring when bruised; cap 3-12cm broad; cap margin striate. This keys to Russula flaviceps Peck using the Trial field key to the species of RUSSULA in the Pacific Northwest (http://www.svims.ca/council/Russul.htm). According to MycoBank, Russula flaviceps Peck is now a synonym of Russula claroflava Grove (http://www.mycobank.org/Biolomics.aspx?Table=Mycobank&MycoBankNr_=187108). I think this is the same species I observed the other day, but failed to collect (http://www.inaturalist.org/observations/881432).
I wish I would have collected this beautiful yellow Russula so that I could have keyed it out.
Bearded milk cap. Growing beneath arctic willow
The Russulaceae are a family of fungi in the order Russulales. According to a 2008 estimate, the family contains 1243 species. Its species typically have fruit bodies with friable, chalk-like stalks, that break with a distinct crack, somewhat like a carrot but with porous flesh (see below). Microscopically, the cells are not all long thin hyphae, which would provide strength and more fibrous appearance when broken. Instead, the flesh contains also many large spherical cells ("sphaerocysts"),...