Detailed microscopical observations on four type specimens of Russula subsect. Lactarioideae from North America are presented and illustrated. As the result of our analyses, all four species are accepted as good species in Lactarioideae, although sometimes with slightly modified concept. R. brevipes is recognized by the rather short and often inflated cells in the pileipellis, large spores with spiny, subreticulate ornamentation and the distinctly amyloid suprahilar spot. Whether or not the European R. chloroides is a later synonym remains to be examined. R. inopina is characterized by filiform, flexuous-undulate terminal cells in the pileipellis, as well as on the gill edge, and it lacks shorter, mucronate pileocystidia. R. romagnesiana, originally described to replace the invalidly published, European R. chloroides var. parvispora, is here considered to be quite different from this European taxon and is accepted as distinct, native American species characterized by having equally small spores, frequently bicapitate pileocystidia near the pileus center as well as hyphal terminations with a glutinous sheath, but lacking distinct incrustations. R. vesicatoria is defined as a species of sandy Pinus stands with crowded gills, large and clavate, obtuse to capitate, often thick-walled pileocystidia, very long and slender hyphal extremities and spores with an inamyloid suprahilar spot. A tentative key to all North American Lactarioideae introduces objective microscopic features for the identification of all recognized species in this group.