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Amanita thiersii

[ Basidiomycetes > Agaricales > Amanitaceae > Amanita . . . ]

by Michael Kuo

Unlike most species of Amanita, which are mycorrhizal, Amanita thiersii is a saprobic decomposer of dead grass roots, and is not found in woods or in association with trees. From a distance, Amanita thiersii is easily confused with Chlorophyllum molybdites, a well known feature of summer lawns across North America. Unlike Chlorophyllum molybdites, however, Amanita thiersii has white gills at maturity--and it is covered from head to toe with shaggy, sticky universal veil material.

Amanita thiersii was originally described from Texas (Thiers, 1957)--but the species has been expanding its range over the last few decades. In my area (central Illinois), it was rarely if ever seen 20 years ago; now it is a very common lawn ornament. It has made its first documented appearances in central Indiana over the last decade, and I have had photos of the species sent to me recently from southern Ohio. The species appears to have a northern limit, perhaps associated with temperature, below the Great Lakes; it has not yet appeared in northern Illinois, even though Chicagoland is much closer to my area than southern Ohio. Then again, prevailing winds here move from west to east, and if spore dispersal via wind currents is the mode of range expansion, this would provide an alternative explanation.

Description:

Ecology: Saprobic in grasses; growing alone, scattered, gregariously, or in arcs and fairy rings in lawns and meadows; summer; south of the Great Lakes (see above).

Cap: 3-15 cm; convex, becoming broadly convex or nearly flat; covered with powdery, shaggy, sticky universal veil material (sometimes washed away by rain); white; the margin hung with veil remnants.

Gills: Nearly free; close or nearly distant; white to creamy; short-gills frequent.

Stem: 8-16 cm long; 1-2 cm wide; with a skirtlike, white ring; bald above the ring; below the ring shaggy and sticky like the cap; volva powdery and indistinct.

Flesh: White; soft; unchanging when sliced.

Odor: Slightly foul.

Spore Print: White.

Microscopic Features: Spores 8-10 µ; globose; smooth; amyloid. Basidia 4-spored, without clamps. Lamellar trama bilateral; subhymenium cellular.

REFERENCES: Bas, 1969. (Thiers, 1957 [A. alba]; Smith, Smith & Weber, 1979; Weber & Smith, 1985; Jenkins, 1986; Metzler & Metzler, 1992; Horn, Kay, & Abel, 1993; Kuo & Methven, 2010; Wolfe, Kuo & Pringle, 2012; Tulloss, 2013.) Herb. Kuo 07280307, 07290301, 07220704, 09100701, 07190807.

Thiers (1957) originally named this species "Amanita alba," but was apparently unaware that the name was already in use; thus Bas (1969) was forced to change the name of the species in order to give it a legitimate name.


Further Online Information:

Amanita thiersii at Studies in the Amanitaceae

 

Amanita thiersii

Amanita thiersii

Amanita thiersii

Amanita thiersii

Amanita thiersii
Cap surface after heavy rains

Amanita thiersii
Spores



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Kuo, M. (2013, May). Amanita thiersii. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/amanita_thiersii.html