Metrodiana 9(2): 47. 1979.
Common Name: none
Synonyms: Calocybe onychina (Fr.) Donk; Lyophyllum onychinum Kühner & Romagn.; Tricholoma onychinum (Fr.) Gillet; Agaricus onychinus Fr.
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.
Rugosomyces onychinus 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, then placed in Calocybe for cytological reasons and now in Rugosomyces for 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 Rugosomyces onychinus are smooth and inamyloid. A similar species, Calocybe carnea has a pinkish rather than purplish cap, and is found occasionally in grassy areas during the summer months
Desjardin, D.E., Wood, M.G. & Stevens, F.A. (2015). California Mushrooms: The Comprehensive Identification Guide. Timber Press: Portland, OR. 560 p.
Donk, M.A. (1962). Generic names proposed for the Agaricaceae. Beih. Nova Hedw. 5: 1-320.
Kalamees, K. (2004). Palearctic Lyophyllaceae (Tricholomatales) in northern and eastern Europe and Asia. Scripta Mycologica 18: Tartu.
Knudsen, H. & Vesterholt, J. ed. (2008). Funga Nordica: Agaricoid, boletoid and cyphelloid genera. 965 p.