Cap 3-5 cm broad, convex, expanding to plano-convex, with or without a low umbo; margin incurved, then decurved, plane to slightly upturned, frequently wavy; surface lavender-purple to vinaceous-purple; when fresh, minutely tomentose (use hand lens), in age blotched shades of purple and brown, eventually entirely brown; context up to 1.0 cm thick, soft, cream-colored, unchanging or darkening slightly; odor mild to slightly farinaceous; taste latently farinaceous to bitter.
Gills sinuate, sometimes with a decurrent tooth, close, golden-yellow to yellowish-buff, in age cream-buff to tan, up to 5 mm broad, edges even; lamellulae in up to three series.
Stipe 2-4 cm long, 1-2 cm thick, more or less equal, sometimes with a basal bend; surface of apex pale-lavender over a pallid ground color, matted tomentose to appressed fibrillose; lower portion fibrillose-striate; context fleshy-fibrous, cream-colored, unchanging; partial veil absent.
Spores 3.5-4.0 x 2.0-2.5 µm, elliptical to oblong-elliptical in face-view, similar in profile, slightly inequilateral with a flat and rounded side, smooth, thin-walled, hilar appendage inconspicuous, inamyloid; basidia with siderophilous granules; spore print white.
Singly or in small groups under conifers; fruiting after fall rains along the coast, in the spring in montane forests; uncommon in most years.
Inedible; unpleasant taste.
Calocybe onychina is a beautiful, seldom collected mushroom characterized by a vinaceous-purple cap and striking yellowish gills. Formerly placed in Tricholoma because of stature and white spores, it is now placed in Calocybe for cytological and molecular reasons. The bright, contrasting colors sometimes cause confusion with Russula species, but these can be distinguished by their brittle structure, i.e. gills that readily shatter and stipes that snap cleanly. Additionally, Russula spores are amyloid ornamented, while those of Calocybe onychina are smooth and inamyloid. A second Calocybe species, Calocybe carnea has a pinkish rather than purplish cap, and is found occasionally in grassy areas during the summer months