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Agrocybe molesta

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

by Michael Kuo

Like other members of the Agrocybe praecox cluster, Agrocybe molesta features a partial veil that usually leaves a ring on the upper stem. Unlike the other members of the cluster, however, it is a devoted decomposer of grass litter, and features spores 10-14 µ long; other praecox-ish species decompose other substrates, and have shorter spores.

It is not always easy to figure out whether a mushroom is a grass-loving saprobe or a wood decomposer, especially if there are trees, woodchips, or even former trees (whose dead root systems extend through the soil) in the vicinity. This means a microscope may be needed to identify Agrocybe molesta with certainty--but the task is still easier than it used to be. To separate Agrocybe molesta (also known as Agrocybe dura) from Agrocybe praecox, field guides emphasize a suite of frustrating minor differences in physical features like the toughness of the stem, the tendency of the cap to crack in old age, the color of the cap, and the precise shade of brown displayed in the mature gills. But recent research has simplified things substantially for this species, allowing us to more or less ignore these differences and focus on the ecology: Agrocybe molesta is the only grass decomposer in the group, though it is variable in many of its physical features.


Ecology: Saprobic, decomposing grass litter; growing alone or gregariously in lawns and other grassy areas; spring and early summer; widely distributed in North America.

Cap: Usually 4-9 cm, but sometimes smaller or larger; convex becoming broadly convex to flat; creamy white, discoloring somewhat--or yellow brown to brown; smooth, but sometimes developing cracks in age; often with whitish partial veil remnants on the margin.

Gills: At first covered by a whitish partial veil; attached to the stem; whitish to pale at first, becoming brown to dark brown or purple-brown; close.

Stem: Usually about 4-10 cm long and .5-1.5 cm thick; more or less equal; smooth to finely hairy; white or brownish; with a thin ring (but the ring often disappears).

Flesh: White.

Taste: Mild, mealy, or slightly bitter to disagreeable; odor not distinctive or mealy.

Spore Print: Dark brown.

Microscopic Features: Spores 10-14 x 6.5-8 µ; more or less elliptical; smooth; slightly truncated; with a pore at one end. Cystidia usually present, but so variable that assessing precise dimensions and shapes is probably a waste of time.

REFERENCES: (Lasch, 1828) Singer, 1978. (Smith, Smith & Weber, 1979; Flynn & Miller, 1990; Phillips, 1991/2005; Lincoff, 1992; Barron, 1999; McNeil, 2006.) Herb. Kuo 06160210.

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