Leucoagaricus americanus

[ Basidiomycetes > Agaricales > Agaricaceae > Leucoagaricus . . . ]

by Michael Kuo

This urban mushroom typically appears in late summer or early fall, in sawdust piles, on wood chips, around waste places or on stumps. It can be fairly easily identified by its distinctive swollen stem, which turns yellow, then slowly reddish, when rubbed. Its cap is scaly, and also turns reddish as the mushroom matures. All but the most recent field guides will list Leucoagaricus americanus as "Lepiota americana," but recent DNA studies indicate the mushroom is more closely related to species like Leucoagaricus naucinus than to species like Lepiota cristata.

Leucoagaricus americanus is a good edible mushroom, but it should only be collected for the table by extremely confident mushroom identifiers; it could be confused with deadly species of Amanita, or with more closely related mushrooms like Chlorophyllum molybdites (which has a greenish spore print and a stem that does not bruise yellow and red). Additionally, its urban habitat frequently places it near roadways, which can mean toxicity from pollution--and it is a species for which "allergic" reactions have been recorded with some frequency.

Description:

Ecology: Saprobic and, in my experience, probably a decomposer of dead wood (I have found it on stumps, in places where trees have been removed, and growing in the crotch of a tree 15 feet above ground); growing alone, scattered or gregariously in lawns and meadows, in sawdust piles or wood chips, near waste places, sometimes on stumps; late summer; widely distributed in North America but found more frequently east of the Rocky Mountains.

Cap: 3-15 cm, oval when young, becoming convex to broadly convex or flat in age; dry; smooth at first; becoming scaly with reddish to reddish brown scales; the center typically remaining smooth in age; whitish but reddening with maturity or after being handled; the margin becoming lacerated and ragged in old age.

Gills: Free from the stem; close; white when young; staining pinkish to reddish brown.

Stem: 7-14 cm long; .5-2.5 cm thick; distinctively swollen towards the base; smooth; firm; white, but soon discoloring reddish to reddish brown; bruising fairly promptly yellow, then slowly reddish, when rubbed; with a high, collarlike ring.

Flesh: White throughout; bruising yellow to orange when young; in age drying reddish; thick.

Odor and Taste: Not distinctive.

Spore Print: White.

Microscopic Features: Spores 8-14 x 5-10 µ; smooth; elliptical; dextrinoid; with a small pore. Cheilocystidia clavate or clavate with a long neck. Pleurocystidia absent. Pileipellis of long, upright, cylindric elements.

Lepiota bresadolae is a synonym.

REFERENCES: (Peck, 1872) Vellinga, 2000. (Saccardo, 1887; Atkinson, 1900; Kauffman, 1918; Kauffman, 1924; H. V. Smith, 1954; Smith, Smith & Weber, 1979; Arora, 1986; Phillips, 1991/2005; Lincoff, 1992; Metzler & Metzler, 1992; Vellinga, 2000; Vellinga, de Kok & Bruns, 2003; McNeil, 2006; Kuo, 2007.) Herb. Kuo 08289702, 09210101, 06300704.

Further Online Information:

Lepiota americana at Roger's Mushrooms

Cheilocystidia

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Cite this page as:

Kuo, M. (2005, October). Leucoagaricus americanus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/leucoagaricus_americanus.html