Observation 4220: Agaricus L.

When: 2007-09-24

Collection location: Madison Heights, Pasadena, California, USA [Click for map]

Who: Jason Hollinger (jason)

No specimen available

In lawn. Cap 2.5 cm, stem 2.5 × 0.4cm. Weak odor, but distinct almondy flavor (chewed on cap). Weak K+y on cap. Cap was pure white on location,but had developed distinct yellow tint by time I arrived home, presumably from bruising/rubbing. Spores 5-6 × 4-5 um. Keyed out using Arora, however spores are a bit too large.

Full notes here.

It seems there is some debate as to what this species might be — I’ll change it back to plain old Agaricus sp.

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Possible undescribed species
By: Nathan Wilson (nathan)
2007-10-05 23:59:47 CDT (-0400)

This looks similar to collections I’ve made in the LA area (e.g., Observation 538) that folks in the LA Mycological Society have called Agaricus arvensis, but which I believe are an undescribed species. True A. arvensis has a smooth cap, a hollow stipe and no sterile margin on the cap. The ones I’ve seen have a fibrillose cap, a solid to slight hollow in the stipe and a sterile cap margin. A. comtulus is an interesting possibility that I hadn’t really considered before. According to Kerrigan in Agaricales of California, A. comtulus is only know from San Francisco Co., but is to be expected elsewhere (Arora says it’s common). However, according to Kerrigan A. comtulus has a strongly hollow stipe and he makes no mention of the cap margin. The spore size matches pretty well with what you measured. I also eliminated it based on size. The ones I saw were often over 5cm broad and Kerrigan lists A. comtulus as having a pileus that’s 2-5cm broad. Yours appear to be in that range, but you also observed the solid stipe. I actually wrote to Kerrigan about this collection and he said that he was not aware of any almond scented Agaricus with a solid stipe.