Amanita thiersii is a species that may have been
introduced to the U.S. It is spreading north and east
from Texas, from which it was originally described. It
is known to be able to digest lawn clippings and
commercially produced cellulose. There is no
known evidence that A. theirsii ever forms
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 × 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 × 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.
The odor is described as indistinct, may become unpleasant in age and then of decay or cheese (associated with yellowing specimens so far as is known). Tthe taste is reported as oily bitter or bitter metallic.
Spores of A. thiersii measure (7.0-) 7.7 - 9.5 (-11.0) × (6.8-) 7.5 - 9.5 (-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.
Developing news: Recent work in the Pringle Lab (Harvard Univ.) has provided DNA-based support for the morphologically-based hypothesis of C. Bas (1969) that species of subsect. Vittadiniae (like A. thiersii were taxa with few "evolved" or "derived" characters (as was said in the 1960's). This has been done by showing that, based on those segments of genetic material that have been sequenced to date, the so-called "least derived" taxa form a group with one or a few ancestors that came into existence very early in the evolution of the genus Amanita. This research is still on-going.
The same research group, with much of the research in the hands of Benjamin Wolfe, also carried out a number of experiments demonstrating that indeed many of the basal taxa are at least capable of living as saprobes. Some species (the number is not yet known) operate only as saprobes. Among these latter is Amanita thiersii. The picture at the head of this paragraph shows a spore of A. thiersii germinating in the laboratory. Wolfe and Pringle have reported that A. thiersii can be grown easily in culture and can live entirely on cellulose in culture. The highest growth rate was recorded for growth on sterilized grass clippings.
In 2009, a grant was sought and received by the Pringle Lab that will result in the sequencing of the entire genome of A. thiersii. Among the goals of having a complete genome for the present species is the study of the origin of ectomycorrhizal symbiosis in Amanita. The genus Amanita is segregated from all other agarics by the process of development of its fruiting bodies from tiny primordia. DNA evidence suggests with high confidence, that the genus is descendant from a single ancestor. This isolated group has, preserved within its present day boundaries, a diverse set of taxa (particularly in sect. Lepidella) that may serve as "genetic snap shots" of one evolutionary history of an ectomycorrhizal "life style." —R. E. Tulloss
The editors of this site owe a great debt to Dr. Cornelis Bas
whose famous cigar box files of Amanita nomenclatural information
gathered over three or more decades were made available to RET for computerization
and make up the lion's share of the nomenclatural information presented on this site.
genitive of Latinized name, "Thiers'" or "of Thiers"
35 - 100 mm wide, white, sometimes becoming yellowish from handling, convex or conico-convex to plano-convex, may become concave after heavy rain (J. McCandless, priv. comm.), mostly with low broad umbo, dry, sometimes slightly viscid in age, subshiny; context white to off-white, unchanging, up to 10 mm thick, thinning evenly to margin; margin nonsulcate, appendiculate with thick flocculence that is continuous with pileus surface, long remaining incurved to decurved; universal veil at first covering surface, white, bruising yellowish when the same is true of exposed pileus in general, soft, subpulverulent, lanose-floccose, squamulose, detersile, in older specimens as scattered remnants (these floccose-fibrillose to felted, patches or scales, sometimes as warts over disk).
free, crowded to close to subdistant, white to yellowish to creamy yellow or yellowish cream in mass, in side view white to cream to yellowish cream to sometimes almost color of egg yolk (in early stages of expansion), rather narrow to broad, with entire to somewhat irregular edge; lamellulae attenuate to subattenuate to rounded truncate to subtruncate, of diverse lengths, unevenly distributed, rather common to plentiful.
80 - 200 × 10 - 20 mm, cylindric, white; base merely a slight enlargement of stipe, subclavate, subfusiform, up to 25 × 22 mm, sometimes with white mycelial “threads” at very bottom; context white, unchanging when cut or bruised (or yellowing except in central cylinder when reaction seen elsewhere in basidiome), stuffed to hollow, with central cylinder 5.5+ mm, with stuffing material dense and white and comprising longitudinally oriented fibrils; partial veil apical, thin, white, easily torn, sometimes ephemeral; universal veil as lanose-floccose covering of stipe below partial veil, in age breaking up into detersile, incomplete, floccose-squamose girdles, finally scant flocculose squamules or scant fibrils.
Odor indistinct, may become unpleasant in age and then of decay or cheese (associated with yellowing specimens so far as known). Taste oily bitter or bitter metallic.
Spot test for tyrosinase (L-tyrosine) - negative. Spot test for tyrosinase (paracresol) - negative throughout basidio,e. Spot test for laccase (syringaldazine) - negative throughout basidiome. Wieland [Meixner] test: negative for amatoxins. Test vouchers: 1.vii.1996 poisoning victim (MEXU), ??. POISONOUS.
George M. Sayers: (1-4) Kansas.
Dr. Jay Justice: (5) Arkansas.
RET: (6-7) Kansas.
Benjamin Wolfe: (8) Used with permission of the Pringle Lab, Harvard Univ. (within text, in vitro).
Brian Adamo: (9-11) Rutherford County, Tennessee, U.S.A. [Note: Original images and additional images can be found at mushroomobserver.org #109254
Each spore data set is intended to comprise a set of measurements from a single specimen made by a single observer;
and explanations prepared for this site talk about specimen-observer pairs associated with each data set.
Combining more data into a single data set is non-optimal because it obscures observer differences
(which may be valuable for instructional purposes, for example) and may obscure instances in which
a single collection inadvertently contains a mixture of taxa.