Agaricus malangelus
(Agaricus xanthodermus, Agaricus sect. Xanthodermatei)

Habitat

Urban lawns, fields, parks and foothills along the front range up into the Juniper and Pinon belt.

Description

We always called these bad smelling, yellow stainer's Agaricus xanthodermus. A. xanthodermus is a close relative in Agaricus section Xanthodermatei known from California and other states. Recent DNA evidence from citizen science collections in Colorado suggest that we have Agaricus malangelus which was described from New Mexico. I believe our Colorado "xanthodermus" is actually Agaricus malangelus which is slightly smaller. We likely have other members of this group in other areas of Colorado. Agaricus iodosmus has been found on the Western slope. Beginners can easily confuse these for other edible Agaricus species such as A. campestris and A. arvensis as they are very similar in appearance.

They are characterized by having a phenolic odor. Smell however is subjective and some people cannot smell the difference. Crush a piece of the stem before smelling to get a stronger odor. It is said that the smell is more pronounced by cooking but I've never tried. The very base of the stipe when nicked, cut or injured will stain bright yellow especially when fresh. Cut a mushroom lengthwise, wait and observe the base to see if its turns bright yellow. The base of the stipe usually has a unique shape to it. The cap is generally deformed marshmallow like, less circular and forms a darker depressed center. The stipe will generally have a thick felt like ring. The appearance can be extremely variable. I've seen both shorter, stalkier and longer skinnier versions. That could be due to weather and environmental factors. I've also seen (forever ago) and heard of a rare yellow stainer from the mountains which is likely a different species in this section. The pictures shown here are from several different collections. Note the yellow staining bases on all of them. This is the tell tail sign. If you learn these basic characteristics it becomes easy to identify these poisonous Agaricus. In general if you do not know Agaricus all that well any yellow staining ones should be avoided. There are several differences between these and those Agaricus in section arvenses. They are also yellow staining, smell pleasant and are generally considered edible. It takes some time to become familiar with them. Smell is one of the quickest ways to differentiate.

Stains bright yellow in KOH.

Location

Colorado Springs

Smell

Phenolic

Spore Print

Chocolate Brown

Edibility

Poisonous

Color

White

iNaturalist Observation

https://www.inaturalist.org/observations/131938036

Last Updated

Jun 25 2025 08:36 AM

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