A sudden appearance of a yellow mushroom, in the shape of a small club or a bowling pin, in your pot might surprise you. This could be the flowerpot parasol (Leucocoprinus birnbaumii), a fungus found in potted plants. Also known as the yellow houseplant mushroom or plant pot dapperling, these small, lemon-yellow mushrooms are about 1 to 3 inches tall. Their bell-shaped or oval caps are 1 to 2 inches in size.  They may appear single or in clusters.

Flowerpot mushrooms thrive in warm, humid environments. Their presence indicates that the soil is healthy and has a high organic matter content. They are a saprotrophic fungus, which means that they break down dead organic matter in the soil, thereby releasing nutrients that can benefit the plant. However, they are toxic to pets and humans. They contain compounds called Birnbaumins, which are poisonous if ingested. Birnbaumins are alkaloids which were first isolated from the flowerpot parasol mushroom.

The cap of a flowerpot mushroom is very fragile. It has a nipple-like centre (umbo) and striations around the edges. 

A mushroom is the reproductive structure of a fungus and lives the rest of its life cycle as a thread-like body in the soil, which is not usually visible. That thread-like body, called a mycelium, could have been introduced to the pot in the potting mix, and that is how they suddenly appear in your flower pot. Another reason could be that a spore of the fungus (similar to a seed) may have floated through the air and landed in your pot, initiating the formation of a fungal colony.

Text and photos by Prerna Jain.