This is one of the most common and morphologically variable, Russula species in the mixed and conifer forests of California and the PNW. For some years it was referred to as Russula mordax sensu Thiers, until the type collection of Russula mordax Burl. 1936 was sequenced. In California it is one of the most common species in mixed woods, but always in the presence of Douglas Fir. I am yet to see it in the pure oak habitat. Despite the variability in appearance, the species has one obvious feature -- it is very slowly, but intensely acrid and the peppery sensation does not wash out easily. The same applies to it closest European relative Russula badia Quél. 1881. One more character by which I have been able to distinguish it in the field is the ribbed surface of the pileal margin in 2/3 of the mature fruitbodies. Yet, many times, I have not been able to achieve positive id, until I taste it... Interestingly, when the pileal coloration is reddish, the stipe also is likely to have pink zones, otherwise rarely.