The yellow houseplant mushroom (Leucocoprinus Birnbaumii) is fairly common in potted houseplants and greenhouses. These mushrooms pop up between summer and fall as a result of spores or mycelium (a network of fungal threads) getting into potting soil, mulch, or in outdoor garden soil.
This mushroom is yellow in color throughout with an oval cap when young which becomes a bell-shape as it ages. T...