Russula sect. Compactae subsect. Lactarioideae contains ten accepted species which may be distinguished on the basis of size of the pileus, taste and odor of the trama, spacing of the lamellae, and color, size, and ornamentation of the spores. Taxa described for the first time are R. inopina, R. cascadensis, R. romagnesiana, R. brevipes var. acrior, and R. b. var. megaspora.
Also review: “Type Studies in Russula Subsection Lactarioideae from North America and a Tentative Key to North American Species,” Cryptogamie, Mycologie 34(3), 259-279, (1 January 2013). https://doi.org/10.7872/crym.v34.iss2.2013.259