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The Genus Agaricus

[ Basidiomycota > Agaricales > Agaricaceae > Agaricus . . . ]

by Michael Kuo

The mushrooms in Agaricus are terrestrial saprobes, and have caps that are not brightly colored. At maturity the gills are free or almost free from the stem, and are brown to chocolate brown. The stem breaks away cleanly from the cap. Agaricus species have a partial veil which often forms a ring on the stem. The spore print is dark brown.

Identification of Agaricus species ranges from fairly easy to very difficult. Characters include bruising reactions of the cap, stem, and flesh--as well as odors and, occasionally, microscopic features. Rub the edge of an Agaricus cap repeatedly in order to assess whether it bruises yellow or not--and be sure to rub the base of the stem, as well. In some species the flesh inside the stem base turns yellow when sliced. Agaricus odors are particularly frustrating for me, since I am apparently "smell blind" when it comes to one of the "distinctive" Agaricus odors: the "phenol" or "library paste" odor of some species. Other species smell like almonds (my sniffer registers this odor just fine), or have non-distinctive odors. Crush the flesh in the base of the stem to assess Agaricus odors.

Agaricus is an imperfectly documented genus in North America, and there is no authoritative contemporary treatise covering the genus across the continent. DNA studies are ongoing (see the references list below) and are beginning to bring the picture into focus--but a substantial amount of collecting and study must still be done (amateur mycologists and mushroom clubs can make substantial contributions in this regard; see Mushrooming in the Age of DNA: Now Comes the Fun Part for more information). For the time being, at any rate, the major species should probably be viewed as tentative "species groups" while we await further research.


Agaricus arvensis
Agaricus arvensis

Agaricus placomyces
Agaricus placomyces

Agaricus bisporus
Agaricus bisporus

Agaricus spore print
Spore Print

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Species Pages:


Arora, D. (1986). Mushrooms demystified: A comprehensive guide to the fleshy fungi. Berkeley: Ten Speed Press. 959 pp.

Bunyard, B. A. et al. (1996). Phylogeny of the genus Agaricus inferred from restriction analysis of the enzymatically amplified ribosomal DNA. Fungal Genetics and Biology 20: 243-253.

Callac, P., et al. (2003). A novel homothallic variety of Agaricus bisporus comprises rare tetrasporic isolates from Europe. Mycologia 95: 222-231.

Callac, P. & Guinberteau, J. (2005). Morphological and molecular characterization of two novel species of Agaricus section Xanthodermati. Mycologia 97: 416-424.

Calvo-Bado, L. et al. (2000). Sexual and genetic identity in the Agaricus section Arvenses. Applied and Environmental Microbiology 66: 728-734.

Challen, M. P. et al. (2003). A phylogenetic reconstruction and emendation of Agaricus section Duploannulatae. Mycologia 95: 61-73.

Chariton, L. R. (1997). Trial field key to the species of Agaricus in the Pacific Northwest. Retrieved from the Pacific Northwest Key Council Web site:

Didukh, M. et al. (2005). Notes on Agaricus section Duploannulati using molecular and morphological data. Mycological Research 109: 729-740.

Dilly, M. (1981). Trial field key to the species of Agaricus in the Pacific Northwest. Retrieved from the Pacific Northwest Key Council Web site:

Freeman, A. E. H. (1979). Agaricus in the southeastern United States. Mycotaxon 8: 50-118.

Freeman, A. E. H. (1979). Agaricus in North America: Type studies. Mycotaxon 8: 1-49.

Hotson, J. W. & D. E. Stuntz (1938). The genus Agaricus in western Washington. Mycologia 30: 204-234.

Kerrigan, R. W. (1979). Studies in Agaricus I. Agaricus pattersonae. Mycologia 71: 612-620.

Kerrigan, R. W. (1985). Studies in Agaricus II: Agaricus lilaceps re-evaluated. Mycologia 77: 137-141.

Kerrigan, R. W. (1985). Studies in Agaricus III: New species from California. Mycotaxon 22: 419-434.

Kerrigan, R. W. (1986). The Agaricales of California 6: Agaricaceae. California: Mad River Press. 62 pp.

Kerrigan, R. W. (1989). Studies in Agaricus IV: New species from Colorado. Mycotaxon 34: 119-128.

Kerrigan, R. W. et al. (1995). Indigenous and introduced populations of Agaricus bisporus, the cultivated button mushroom, in eastern and western Canada: Implications for population biology, resource management, and conservation of genetic diversity. Canadian Journal of Botany 73: 1925-1938.

Kerrigan, R. W., P. Callac, J. Xu & R. Noble (1999). Population and phylogenetic structure within the Agaricus subfloccosus complex. Mycological Research 103: 1515-1523.

Kerrigan, R. W. (2005). Agaricus subrufescens, a cultivated edible and medicinal mushroom, and its synonyms. Mycologia 97: 12-24.

Kerrigan, R. W., P. Callac, M. P. Challen & L. A. Parra (2005). Agaricus section Xanthodermatei: a phylogenetic reconstruction with commentary on taxa. Mycologia 97: 1292-1315.

Mitchell, A. D. & Brseinsky, A. (1999). Phylogenetic relationships of Agaricus species based on ITS-2 and 28S ribosomal DNA sequences. Mycologia 91: 811-819.

Robison, M. M. et al. (2001). A phylogeny of the genus Agaricus based on mitochondrial atp6 sequences. Mycologia 93: 30-37.

Smith, A. H. (1940). Studies in the genus Agaricus. Papers of the Michigan Academy of Science 24: 107-138.

Smith, A. H., Smith, H. V. & Weber, N. S. (1979). How to know the gilled mushrooms. Dubuque, Iowa: Wm. C. Brown. 334 pp.

Cite this page as:

Kuo, M. (2007, August). The genus Agaricus. Retrieved from the MushroomExpert.Com Web site: