Lepiota lutea: Leucocoprinus birnbaumii
Cap 2.0-5.0 cm broad, obtuse-conic to bell-shaped, broadly conic in age, margin at first incurved, then decurved to plane, conspicuously striate; surface more or less smooth at the disc, elsewhere sqaumulose or matted tomentose; color bright yellow to fluorescent yellow, soon fading to dingy, pale yellow; flesh thin, soft, fragile, unchanging; odor: strongly of "mushrooms;" taste, mild.
Gills free, close, moderately broad, thin, fragile, pale yellowish, the edges slightly darker.
Stipe 2.5-7.0 cm long, 2-6 mm thick, round, slender, hollow to stuffed at maturity, equal except for an often enlarged base; surface matted fibrillose, especially at the apex, obscurely so below, especially in age or after handling; color like the cap, soon fading to pale yellow; veil membranous, pubescent, forming a narrow, fragile, superior annulus.
Spores 7.5-11 x 6-7 microns, oval to broadly elliptical, smooth, thick-walled, dextrinoid, with an apical germ pore.
Solitary, scattered to clustered on the soil of potted greenhouse plants; occasional outdoors in grass or well-decayed wood chips; fruiting year-round in greenhouses, restricted to late summer or early fall outdoors.
Possibly poisonous, to be avoided.
This diminutive mushroom, typically found on the soil of potted indoor plants, is easily recognized by a bright-yellow (when fresh, it fades rapidly in the sun), finely-scaled, bell-shaped, striate cap, thin, collar-like annulus, and free, yellowish gills. A close relative is Leucoprinus cepaestipes which has a white, striate cap and fruits outdoors on well rotted wood chips or in grass under conifers.