Clitocybe rivulosa
Führ. Pilzk.: 122. 1871.
Common Name: sweat-producing Clitocybe
Synonym: Clitocybe dealbata var. rivulosa (Pers.) P. Kumm.
Misapplied name: Clitocybe dealbata (Sowerby) Gillet
Cap 2.0-4.0 cm broad, shallowly convex in youth, expanding to nearly plane with a slightly depressed to umbonate disc; margin incurved, then decurved to occasionally raised in age; surface canescent, white, ashy-grey to greyish-tan; streaked or water-spotted at maturity; context thin, 3.0-4.0 mm thick at the disc, 1-2 mm at the margin; context soft, cream-buff, unchanging; odor mild; taste mild to slightly astringent with time.
Gills adnate at first, subdecurrent in age, close, cream-buff, becoming tan, relatively narrow; lamellulae in three to four series.
Stipe 2.0-4.0 cm long, 4.0-8.0 mm thick, equal to enlarged at the apex, straight or curved, solid in youth, eventually hollow, often flattened in cross section, not leathery or tough; surface appressed fibrillose, pallid, darkening where handled; partial veil absent.
Spores 4.0-5.0 x 2.0-3.0 µm, smooth, thin-walled, elliptical-oblong in face-view, elliptical and inequilateral in profile, hilar appendage well-developed, inamyloid; spores white in deposit.
In arcs and rings in grasslands and pastures; fruiting from late fall to mid-winter; infrequent to occasionally common.
Toxic; contains muscarine.
Clitocybe rivulosa is a toxic look-alike of the edible Fairy-Ring Mushroom, Marasmius oreades. Both occur in grass and are similar in size. Marasmius oreades differs, however, in having a uniform, buff to tan-colored cap, not pale-grey and streaked, more widely spaced adnexed to adnate gills as opposed to subdecurrent, and a leathery, tough stipe. Additionally, fruiting bodies of Marasmius oreades revive after drying, a feature absent in Clitocybe rivulosa. Two subspecies and several varieties have been described, an indication of its variability. Here it is treated as a single species.
Ammirati, J.F., Traquair, J.A. & Horgen, P.A. (1985). Poisonous Mushrooms of the Northern United States and Canada. University of Minnesota Press: Minneapolis, MN. 396 p.
Arora, D. (1986). Mushrooms Demystified. Ten Speed Press: Berkeley, CA. 959 p.
Bigelow, H.E. (1982). North American Species of Clitocybe. Part I. J. Cramer: Vaduz, Liechtenstein. 280 p. (PDF)
Breitenbach, J. & Kränzlin, F. (1991). Fungi of Switzerland. Volume 3: Boletes and Agarics (1st Part). Strobilomycetaceae, Boletaceae, Paxillaceae, Gomphidiaceae, Hygrophoraceae, Tricholomataceae, Polyporaceae (lamellate). Verlag Mykologia: Luzern, Switzerland. 361 p.
Desjardin, D.E., Wood, M.G. & Stevens, F.A. (2015). California Mushrooms: The Comprehensive Identification Guide. Timber Press: Portland, OR. 560 p.
Gregory, D. (2007). The genus Clitocybe of California. Masters Thesis. San Francisco State University.
Knudsen, H. & Vesterholt, J. ed. (2008). Funga Nordica: Agaricoid, boletoid and cyphelloid genera. Nordsvamp: Copenhagen, Denmark. 965 p.
Knudsen, H. & Vesterholt, J. ed. (2012). Funga Nordica: Agaricoid, boletoid, clavarioid, cyphelloid and gastroid genera. Vol. 1. Nordsvamp: Copenhagen, Denmark. 511 p.
Siegel, N. & Schwarz, C. (2016). Mushrooms of the Redwood Coast. Ten Speed Press: Berkeley, CA. 601 p.