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The Agrocybe praecox cluster

[ Basidiomycetes > Agaricales > Bolbitiaceae > Agrocybe . . . ]

by Michael Kuo

The mushrooms in the Agrocybe praecox species cluster feature brown spore prints, whitish to yellowish brown caps, and partial veils that often leave fragments hanging from the cap margins and fragile rings on the stems. The mushrooms range from small to medium in size, and are often found in urban settings--though some species occur in woods, as well.

Research by Flynn and Miller (1990) determined at least five biological species in the Agrocybe praecox cluster, four of which occur in North America. A "biological species" is defined on the basis of whether the organisms can mate and produce offspring--regardless of what they look like (think of dobermans and dachshunds, both of which are Canis familiaris). The four North American praecox species vary so widely in their physical features, according to the authors, that traditional identification methods (careful observation, microscopic analysis) are pretty much useless.

Fortunately for those of us who want to identify our finds, Flynn and Miller found parallels between mating compatibility and ecology; the four North American biological species in the praecox cluster can be grouped according to their ranges and the type of organic material the mushrooms decompose:

Agrocybe molesta is the only grass-decomposing biological species in the group. It is widely distributed in North America, appearing in spring and early summer.

Species II  decomposes the fragmented wood litter of conifers or aspens in western North America's forests, appearing in spring (which can come quite late at high elevations).

Species III  decomposes the fragmented wood litter of hardwoods in eastern North America's forests, appearing in spring and summer. Occasionally, Species III fruits from fallen logs and stumps. Maple trees are often present, and Species III may correspond to "Agrocybe acericola"--but that species, which was defined on the basis of subtle differences in physical features, would need to be redefined for the name to represent a natural organism.

Species I  "usually occurs in urban habitats where fragmented wood chips are used to mulch ornamental plantings" (1107). It appears in spring and summer, and often reappears in fall at about the time Agaricus campestris appears.

Thus the species can be sorted out fairly easily, unless your Agrocybe praecox was growing in grass, a few feet away from woodchips, at the edge of a lawn abutting a mixed conifer-hardwood forest in the Panhandle of Nebraska--in which case you will probably have trouble figuring out which ecological lines to draw. Still, even this challenge seems less daunting than figuring out whether your mushroom's cystidia are "clavate-utriform" or merely "utriform," which is the kind of thing you would have been faced with before Flynn and Miller's research.


Ecology: Saprobic on woody debris; growing alone or gregariously; spring, summer, and fall; widely distributed in North America. See the material above for more precise information.

Cap: Small or medium in size (rarely larger than 10 or 12 cm across); convex becoming broadly convex or flat, often with a low central bump; smooth, but sometimes developing cracks in age; color ranging from whitish to yellow-brown or brownish (but not often dark brown); sometimes with whitish partial veil remnants on the margin.

Gills: At first covered by a white partial veil; attached to the stem or pulling away from it; close; whitish to pale at first, becoming brown to cinnamon brown.

Stem: Dimensions variable, but not often wider than 1.5 cm or longer than 10 cm; more or less equal; smooth to finely hairy near the apex; whitish or pale brownish; with a thin, whitish ring which often disappears; with white rhizomorphs attached to the base.

Flesh: Whitish; not particularly thick in the cap.

Taste: Mealy; odor mealy.

Spore Print: Dark brown.

Chemical Reactions: KOH on cap surface negative or yellowish.

Microscopic Features: Spores 8-11 x 5-6 µ; more or less elliptical; smooth; with a pore at one end; slightly truncated. Cystidia present, but assessing sizes and shapes is apparently not informative in identification.

REFERENCES: (Persoon, 1800) Fayod, 1889. (Smith, Smith & Weber, 1979; Arora, 1986; Flynn & Miller, 1990; Phillips, 1991/2005; Lincoff, 1992; Evenson, 1997; Barron, 1999; Roody, 2003; McNeil, 2006.) Herb. Kuo 05030311, 05260307, 06040301, 05290402, 08300402, 05020605, 05040601, 05050602.

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Agrocybe praecox

Agrocybe praecox

Agrocybe praecox

Agrocybe praecox

Agrocybe praecox

Agrocybe praecox

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Kuo, M. (2006, September). Agrocybe praecox. Retrieved from the MushroomExpert.Com Web site: