Mushroom Mystery: Identifying Yellow Fungi

Yellow mushrooms are a common sight in gardens and houseplants, and are often a cause for concern. The most common variety is Leucocoprinus birnbaumii, also known as the yellow parasol mushroom, the painted dapperling, or the flowerpot parasol. This species is toxic to humans and pets, and can spread easily through spores in the soil. Other types of yellow mushrooms include the yellow patches mushroom, the yellow fieldcap mushroom, and the golden oyster mushroom, which is popular for cooking. While the presence of yellow mushrooms may indicate overwatering, it is more likely due to contaminated potting soil.

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Leucocoprinus birnbaumii

The species was first described as Agaricus luteus in 1788 by the English mycologist James Bolton, who observed it in a hothouse near Halifax in 1785. At the time, gilled species were classified as Agaricus, and luteus comes from the Latin for yellow or yellow-orange. Bolton suggested the common name of 'Yellow Cottony Agaric' in reference to the soft, scaly texture of the mushroom. However, the name A. luteus had already been used to describe an unrelated Russula species, published in 1778 by William Hudson.

In 1839, the Czech mycologist August Corda described the same species from Prague, where it was found growing in a greenhouse between pineapple plants by a garden inspector named Birnbaum. He called it Agaricus Birnbaumii. The French mycologist Marcel Locquin classified it as Leucocoprinus luteus in 1945, and the German mycologist Rolf Singer reclassified it as Leucocoprinus birnbaumii in 1962.

The mushroom thrives in warm, humid environments and moist soil, so it can appear in houseplants or greenhouses year-round. The spores are commonly introduced by contaminated soilless mix, and humans, pets, and even air can also sometimes bring spores in from outside. It is adept at spreading via potting soil and transplanted plants, so if you don't want a house full of yellow mushrooms, it is recommended to remove the plant from the house or attempt spore removal.

Yellow parasol mushroom

The yellow parasol mushroom, also known as Leucocoprinus birnbaumii, is a species of gilled mushroom in the family Agaricaceae. It is common in the tropics and subtropics and frequently occurs in greenhouses and flowerpots. The French mycologist Marcel Locquin classified it as Leucocoprinus luteus in 1945, and the German mycologist Rolf Singer reclassified it as Leucocoprinus birnbaumii in 1962.

The yellow parasol mushroom is easily recognisable by its small size and bright lemon yellow oval or bell-shaped cap that fades to white with age. They can grow outdoors in clusters or singularly, but they most commonly occur in potted plants, greenhouses, and compost piles where they thrive in warm, moist conditions. In outdoor conditions, they are most often seen in the summer, while in indoor conditions they appear year-round. They work to break down organic matter found in soils and they do not harm living plants.

The mushroom spores infect the soil and are widely distributed as it is packaged and shipped. Infection can happen at any point, from a contaminated ingredient from a factory or farm to spores on the clothes of an employee. The spores can also be introduced by humans, pets, or even air from outside. Overwatering of potted plants can also cause the mushrooms to appear, and they are difficult to manage once established.

The yellow parasol mushroom is considered inedible and toxic, although the exact toxicity is unknown. Therefore, it is recommended to remove the mushrooms as soon as they appear if pets or small children reside in the home. To get rid of the mushrooms, you can remove the plant from the house, attempt spore removal by picking off visible mushrooms, or replace the soil entirely.

Toxicity and edibility

Leucocoprinus birnbaumii, commonly known as the yellow parasol, flower pot parasol, or plantpot dapperling, is a toxic mushroom species. While the exact toxicity is unknown, the mushroom is considered inedible and may be poisonous to pets and humans. If you have small children or pets, it is recommended to remove the mushrooms from your houseplants to prevent accidental ingestion.

The mushroom is identified by its bright to pale yellow colour, including the inner flesh, and its oval or bell-shaped cap, which can grow up to two inches in diameter. As the mushroom ages, the cap expands and opens up to a wider, parasol shape, and the colour fades to pale yellow or brown. The gills of the mushroom are typically yellow but can turn brown with age, and they do not attach to the stem. The stalk, or stipe, is a few inches tall and usually has a ring around it, although this ring may disappear as the mushroom matures.

Leucocoprinus birnbaumii thrives in warm, humid environments and is commonly found in potted plants and greenhouses. The mushroom spores can infect the soil, and the contamination can occur at any point during the packaging and shipping process. The spores can also be introduced by humans, pets, or air from outside. While the mushrooms are not harmful to plants and may even provide benefits, it is important to prevent the spread of the spores by removing the mushrooms as soon as they appear and replacing the contaminated soil.

It is important to distinguish Leucocoprinus birnbaumii from other yellow mushroom species, such as Leucocoprinus straminellus, which is a paler shade of yellow, or Leucocoprinus flavescens, which typically has a brown area in the centre of the cap. Additionally, there are other types of yellow mushrooms, such as Golden Oysters, which are edible and sought after by foragers, and Yellow Patches, which are not poisonous despite some claims. Proper identification of mushroom species is crucial to determine their toxicity and edibility.

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Removal and prevention

Leucocoprinus birnbaumii, commonly known as the yellow parasol mushroom, is a species of gilled mushroom that is toxic to humans and pets. It is common in the tropics and subtropics and frequently occurs in greenhouses and flowerpots. If you want to get rid of these mushrooms, here are some steps you can take:

• Remove the plant from the house: Put the plant outside or get rid of it entirely. This is the simplest solution if you want to avoid having a house full of yellow mushrooms.
• Attempt spore removal: Pick off all visible mushrooms from their base to prevent them from releasing spores and spreading. However, this may not be effective if the fungus has deeply infested the soil.
• Replace the soil: Remove the plant from the pot, shake off the roots, and replant it in fresh, uncontaminated soil. If replanting is not possible, remove the top two inches of soil.
• Use fungicide: Treat the plant's substrate with a fungicide like Copper. However, Leucocoprinus birnbaumii is pretty resilient, and fungicides may not always work.
• Alter the conditions: Mushrooms thrive in warm, humid environments with moist soil. Try to reduce the humidity, lower the temperature, or improve airflow to prevent the mushrooms from growing.

To prevent Leucocoprinus birnbaumii from appearing in the first place, avoid using contaminated potting soil or mulch. The mushroom spores can infect the soil during packaging, shipping, or through external factors like spores on employees' clothes. Additionally, be cautious when introducing new plants to your home, as the spores can spread to other plants.

If you live in an area with a cold winter, leaving the plant outside during the winter will likely kill the fungus. Leucocoprinus birnbaumii is not winter-hardy in most of the continental USA or Canada and prefers warm, moist soil.

Other types of yellow mushrooms

There are several other types of yellow mushrooms, including:

• Golden oyster mushrooms: These mushrooms exhibit a striking yellow colour and are popular for cooking, with a mild, delicate flavour and velvety texture. They are native to eastern Russia, northern China, and Japan, and are one of the most popular wild mushrooms eaten in Russia. They have been introduced to North America, where they can now be found in several states.
• Golden waxcaps: These mushrooms feature a bright yellow stem and cap, with caps that are sticky to the touch when young. They can grow up to four inches tall with a nearly two-inch cap. They are often found growing under different types of trees in different regions, such as coastal redwoods on the west coast of North America and beech trees on the east coast.
• Yellow fieldcap mushrooms: These mushrooms typically appear wherever organic matter is plentiful. They have little yellow heads that pop up in clusters of bell-shaped caps with thin, white stems. Their gills turn from yellow-white to brown as they age, and their caps expand until they flatten out. They grow to about five inches tall with caps approximately two inches wide.
• Yellow patches mushrooms: This variety of mushroom has a rounded, yellow-orange cap that is either smooth or has small warts on its surface, and a tall, pale stem. Their sticky caps can grow to about four inches wide on a stem up to four inches tall. They are commonly found in the central and eastern parts of North America, appearing in naturalized areas with lots of organic matter.
• Leucocoprinus straminellus: This variety is closely related to Leucocoprinus birnbaumii, but is generally a paler shade of yellow. It is a tropical or subtropical mushroom, so finding it in nature in the continental US, Canada, or northern Mexico is extremely rare, but it is commonly found in potting and gardening soil.

Frequently asked questions