Agaricus xanthodermus
Description
Agaricus xanthodermus, commonly known as the yellow-staining mushroom, is a species of fungus in the family Agaricaceae. This species is notable for its characteristic yellow discoloration when bruised or cut, which is a key identifying feature. It is widely distributed across Europe and North America and can be found in various habitats, including grasslands, gardens, and woodlands.
Taxonomy and Nomenclature
The species was first described by the French mycologist Léon Louis Rolland in 1876. The genus name Agaricus is derived from the Greek word agarikon, which refers to a type of tree fungus. The specific epithet xanthodermus comes from the Greek words xanthos meaning yellow and derma meaning skin, referring to the yellow staining of the mushroom's flesh.
Morphology
Cap
The cap of Agaricus xanthodermus is convex to flat, measuring 5–15 cm in diameter. It is white to cream-colored and often exhibits a slight yellowish tinge, especially towards the center. The surface is smooth and dry, sometimes cracking with age.
Gills
The gills are free from the stem, crowded, and initially white, turning pink and eventually dark brown as the spores mature. This color change is typical of many Agaricus species.
Stem
The stem is 6–12 cm long and 1–2 cm thick, cylindrical, and often slightly bulbous at the base. It is white and discolors to yellow when bruised. The stem has a persistent ring, which is white and membranous.
Flesh
The flesh is white but quickly turns yellow when cut or bruised, especially at the base of the stem. This yellowing reaction is due to the presence of phenolic compounds.
Spores
The spores are dark brown to black, smooth, and elliptical, measuring 5–7 by 4–5 µm. The spore print is dark brown.
Chemical Composition
Agaricus xanthodermus contains several bioactive compounds, including phenolic compounds responsible for its yellow staining. It also contains hydrazine derivatives such as agaritine, which are toxic and can cause gastrointestinal distress in humans. The presence of these compounds makes the mushroom inedible and potentially harmful if consumed.
Habitat and Distribution
Agaricus xanthodermus is a saprotrophic fungus, meaning it derives nutrients from decomposing organic matter. It is commonly found in grassy areas, gardens, parks, and woodland edges. The species is widely distributed across Europe and North America, with occurrences reported in other temperate regions worldwide.
Ecological Role
As a saprotroph, Agaricus xanthodermus plays a crucial role in the decomposition of organic matter, contributing to nutrient cycling in ecosystems. It helps break down complex organic materials, releasing nutrients back into the soil, which benefits plant growth.
Toxicity
Agaricus xanthodermus is considered toxic due to its content of phenolic compounds and hydrazine derivatives. Ingestion can cause symptoms such as nausea, vomiting, abdominal pain, and diarrhea. The yellow-staining reaction serves as a warning sign of its toxicity. It is important to distinguish this species from edible Agaricus species, such as Agaricus bisporus (the common button mushroom).
Identification
The key identifying feature of Agaricus xanthodermus is its yellow staining when bruised or cut. This reaction is immediate and can be observed on the cap, gills, and stem. Other distinguishing characteristics include the white to cream-colored cap, free gills that change color with age, and the presence of a persistent ring on the stem.
Similar Species
Several other Agaricus species can be confused with Agaricus xanthodermus, including:
- Agaricus arvensis - Known as the horse mushroom, it lacks the yellow staining reaction and has a more robust stature.
- Agaricus campestris - The field mushroom, which also lacks the yellow staining and has a pink to brown spore print.
- Agaricus bisporus - The common button mushroom, which is widely cultivated and lacks the yellow staining.