Technical description not yet available.

BRIEF DESCRIPTION: The cap of A. theirsii is 35 - 100 mm wide, convex to conico-convex to plano-convex, mostly with a low, broad umbo, white, dry, sometimes slightly viscid with age, with a non sulcate, appendiculate margin; cap flesh up to 10 mm thick. At first the cap is entirely covered by soft, subpulverulent, lanose-floccose, squamulose, white volva; later becoming more or less glabrous with scattered, floccose-fibrillose to felted, patch- or scale-like, at center sometimes wart-like remnants of volva.

The gills are crowded to subdistant, free, rather narrow to broad.  In mass they appear  white to yellowish to creamy yellow or yellowish cream.  In side view they are white to cream to yellowish cream to sometimes almost color of egg yolk (in early stages of expansion).  The short gills are attenuate to subattenuated to subtruncate to rounded-truncate, of many lengths, unevenly distriubted, and rather common to plentiful..

The stem is 80 - 200 x 10 - 20 mm, equal, stuffed to hollow, white, bruising yellow in some specimens (associated with yellowing in other parts of the fruiting body and an odor of cheese). The bulb is merely a slight broadening of the stipe base, e.g., 25 x 22 mm.  At first, below the ring is densely covered by lanose-squamulose volva, with age breaking into easily removable, incomplete, floccose-squamose girdles, finally becoming scanty flocculose-squamulose to merely fibrillose.

Spores of A. thiersii measure (7.3-) 7.8 - 9.8 (-11.0) x (7.0-) 7.3 - 9.0 (-10.0) µm and are globose to subglobose (rarely broadly ellipsoid) and amyloid. Clamps are absent from bases of basidia.

There is a plausible report of a case of serious POISONING attributed to this species, from the state of Puebla, Mexico (Tulloss, unpub.data). As far as I know the outcome of the poisoning is unknown. Given other recent poisonings by taxa of section Lepidella, one might expect A. thiersii to halt kidney function at least temporarily when ingested by humans.  A Wieland [Meixner] test on the material involved in the cited poisoning case was negative for amatoxins.  More information on poisoning by A. thiersii and other amanitas of subsection Vittadiniae is desired by the editors of these pages.

Specimens with yellow bruising reactions and/or an odor of cheese may be infected by one or more hyphomycetes as has been noted in other taxa such as A. subsolitaria (Murrill) Murrill and A. polypyramis (Berk. & Curt.) Sacc.

The species is found in grassy areas distant from trees, such as in lawns and public parks. It is known from Illinois and Kansas, U.S.A. to the state of Puebla, Mexico.

Bas created stirps Thiersii in which the present species is placed along with A. albofloccosa A. V. Sathe & S. D. Deshp. (SW India), A. aureofloccosa Bas (Republic of Congo), A. foetens Singer (Argentina), and A. praeclara (Pearson) Bas (South Africa). -- R. E. Tulloss

Photo courtesy of Dr. Jay Justice (Arkansas)

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Last change 19 April 2006.
This page is maintained by R. E. Tulloss.
Copyright 2003, 2004, 2006 by Rodham E. Tulloss.
Photograph copyright 2003 by Dr. Jay Justice.