Russula krombholzii

Common Name: Blackish-Red Russula
Description: Cap 4-10 cm across, convex then flattened with a slight depression; dark blackish purple at center, paler, more blood red at margin, often mottled with paler discolored areas; smooth, slightly viscid when wet. Stem 30-60 by 10-20 mm high and wide.
Habitat: usually under oak or other deciduous trees.Common. Found widely throughout northeastern North America. west to Michigan.
Edible: Yes.

Source: Mushrooms of North America by Roger Phillips.