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Fungi: Basidiomycota


Agaricus xanthodermus (a.k.a. Yellow Stainer)

A. Species Name

  • Agacricus xanthodermus

B. Native Enviroment

  • Substrate: on the ground.
  • Habitat: in clusters or large troops in lawns among grass, or in garden beds among leaf litter. Mostly in urban areas, sometimes in bushland, but then usually in disturbed areas such as around picnic areas or where the understorey has been cleared. They commonly grow among oak trees.
  • Distribution: SA, QLD, NSW, VIC, TAS.; cosmopolitan.
  • Conservation status: common and widespread. May be an introduced species.
  • Scattered, gregarious, or in broad arcs in a variety of habitats: under conifers, hardwoods, in grass and in gardens
  • Fruiting throughout the year when moisture is available, but most abundant from early fall to mid-winter.

C. Characteristics of the Organism

  • Cap: 50-200 mm diameter, at first globose or hemispherical (but usually rather square in profile), then convex to plane. Surface white, eventually off white, but in age the cap often becomes brown or greyish brown in the centre, and may eventually be entirely gray.
  • Gills: crowded, free, at first white, then deep flesh pink, eventually brown then dark purplish brown.
  • Flesh: white, bruising yellow on cutting. Even in old specimens, the flesh inside the base of the stem will bruise yellow (cut stem in half).
  • Odour: strong chemical odour, of phenol (also has been described as Carbolic or like Indian Ink or iodine).
  • Spore print: dark purplish brown.

Distinctive characteristics
  • The surface of the cap and stem stain bright yellow on bruising or scratching.
  • The yellow stain is particularly obvious if the stem is split in two and the flesh at the stem base is rubbed.
  • The cap is a little squarer than other species of Agaricus - especially in the button stage.
  • There is an unpleasant odour - like a disinfectant.
  • The odour and the yellow stain become more noticeable on cooking.

Similar species
  • The Yellow Stainer is very similar in appearance to the Cultivated Mushroom (Agaricus bisporus) and to edible wild mushrooms such as the Field Mushroom (Agaricus campestris). wild mushrooms such as the Field Mushroom (Agaricus campestris).

D. Adaptations to the Environment

  • An adaptaion to the enviroment is how the fruiting body is yellow in colour. In nature, and by other creatures, yellow is considered a sign of danger.
  • The fruiting body has probably evolved to be yellow, becuase it is a colour that will be less likely to be eaten by animals.
  • Another adaptation was to become toxic which is dangerous to smaller animals and painful to larger animals. This adaptaion helps keep the fruiting body productive.

E. Ecological and Medical Roles

  • Basidiomycetes are of immense ecological and industrial importance in their mycorrhizal associations with forest trees and many other plants. Mycorrhiza is a symbiotic associaton between fungi and plant roots, form which both benefit. They advantages for the fungi are that the plants with which they are associated pass on photosynthetic products to them, and in turn the fungi provide the plants with mineral nutrients, which they can extract more efficiently from the soil. Many pioneer plants of poor soils are extremely dependent on these mycorrhizal fungi. Plants may form mycorrhizal associations with many fungal species.

F. A Picture or Sample of the Organism

Three Images of Agaricus xanthodermus

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