Leucocoprinus birnbaumii (Corde) Singer syn. Leucocoprinus flos-sulfuris (Schnitz) Cejp Lepiota lutea (Bolton) Quél. Cap 2.5-6cm across, oval becoming broadly conical or bell-shaped then umbonate and flat, with the margin distinctly lined in mature specimens; bright yellow to greenish yellow or pale yellow or white, the disc sometimes darker or more brownish; dry, powdery to mealy or minutely scaly in age. Gills free, crowded; yellow or pale yellow. Stem 30-100x 1-5mm, slender, but slightly enlarged at the base; yellow; dry, smooth, or powdery. Veil yellow partial veil forms a small, collar-like ring on the upper stalk which may disappear. Flesh very thin; yellow. Spores ellipsoid, with an apical pore, smooth, dextrinoid, 8-13 x 5.5-8µ. Deposit white. Habitat singly or in groups or dense tufts on rich organic matter and on compost, decaying hay, and leaf piles; also in gardens and lawns in the South. Common in the South. Found in Europe and widely distributed in many parts of North America; indoors (greenhouses) in the North, outdoors in warmer areas. Season May-September, anytime indoors. Not edible - reported as poisonous to some people. Many thanks to Rachel Inbar for the pictures of the almost white form.