Cap 1.5-4.5 cm broad, convex, nearly plane in age, often umbonate; surface at first smooth, reddish-brown at the disc, shading to a lighter margin, the cuticle, except at the disc, soon breaking up into concentrically arranged scales revealing underlying white tissue; flesh thin, white; odor pungent.
Gills free, close, white to cream.
2.5-6 cm tall, 0.2-0.4 cm thick, hollow, slender, equal to slightly enlarged at the base; surface white, smooth or with a scattering of fibrils; veil membranous forming a fragile, superior ring.
Spores 6-7.5 x 3-4.5 µm, wedge-shaped, spurred, smooth and dextrinoid; spore print white.
Solitary to scattered under conifers, especially Monterey cypress and redwood; fruiting from early fall to mid-winter.
Unknown; to be avoided as some small Lepiotas contain the same deadly toxins as Amanita phalloides (Death Cap).
Lepiota castaneidisca belongs to a group of small Lepiotas that can be difficult to tell apart. A combination of characters help to distinguish it from related species: a concentrically-scaled cap, smooth disc and stipe, unchanging color when bruised, pungent odor and wedge-shaped, dextrinoid spores. Note, caps may vary from finely to moderately scaled depending on weather conditions.
Lepiota castaneidisca is common in the San Francisco Bay Area, where it has long been mis-identified as Lepiota crista. Lepiota castaneidisca is probably a California endemic species, whereas Lepiota cristata is widespread in the Northern Hemisphere.