Leucocoprinus birnbaumii (MushroomExpert.Com)
Leucocoprinus birnbaumii [ Basidiomycota > Agaricales > Agaricaceae > Leucocoprinus . . . by Michael Kuo. I receive many frantic e-mails about this little yellow mushroom, since it has a tendency to pop up unexpectedly in people's flower pots—even indoors!