Cap 2-6 cm broad, conic, becoming broadly convex with age; surface smooth, viscid, yellow to bright yellow when fresh, fading to whitish or greyish; margin striate; flesh thin, very fragile.
Gills adnate to adnexed, close, sometimes free, yellowish, to yellowish-brown at maturity.
Stipe 6-11 cm long, 2-5 mm thick, equal to slightly enlarged at base, hollow, fragile, pale yellow, partial veil absent.
Spores 10-14 x 6-9 µm, elliptical, smooth, with a germ pore. Spore print rusty brown.
Scattered on grass and dung. Fruits throughout the year whenever moisture is available.
Edible, but too small and fragile to be of any interest.
Bolbitius vitellinus is a small, yellow, attractive mushroom that is easily recognized by its viscid, striate cap, yellow brown gills, rust-brown spores, lack of a ring, and habit of growing either on dung or grass. Like many small Coprinus (s.l.) species, fruitings are ephemeral, mushrooms opening in the morning, then shriveling by the end of the day. Occasionally, unusually robust specimens are found which may persist for several days. Leucocoprinus birnbaumii, a tropical species which in the Bay Area occurs mostly in greenhouses, is similar in size and cap color but the cap is not viscid, the gills are free, there is a ring, and the spores are white.