This red-stainer definitely deserves the code letter "V" for the flesh discoloring, but even cap color is a question...
To further narrow our choices in Kibby & Fatto's key, we can attempt to find another certain feature. However, I failed to capture much more than the color change. I think I am seeing some bites where I tasted the cap but nothing rejected, and therefore assume that this species is not spicy tasting. So, that gives us "T"
EHKM PTV - Group 42; ...QTV - magna; EHKN PYV - albonigra; EIKM PTV - compacta; EIKN QTV - brunneoalba; FHKM PTV - Group 42; ...QTV - " ; FHKN PTV - decora; ...QTV - Group 46; ...RTV - faginea; FIKM PTV - compacta
We do end up confirming the white stem by looking at the choices listed above. But I am still wondering about the taste... R. nigricans would enter back into this discussion with the presence of a spicy taste. See this article:
A Deadly Russula
Also included here are images of blackening in older specimens.
H = Adnate cuticle, peels to the margin of cap or up to 1/3 of radius
K = White stem
M = 10 - 20 cm (4 - 8 in.)
we don't have indication of the spore color, except that the gills are cream-colored (for what that is worth)
S = Acrid, hot, or peppery taste
V = Flesh discolors when cut or bruised
FHKM PSV R. dissimulans