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. thiersii 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.
This species is found in grassy areas distant from
trees, such as in lawns and public parks. It
is now known from as far north as Indiana, Illinois,
Kansas, and Maryland, U.S.A. and southward
to the state of Puebla, Mexico.
Unjustified claim of toxicity:
About two decades ago there was a report of a case
of serious poisoning attributed to this
species, from the state of Puebla, Mexico (Tulloss,
unpub. data). The outcome of the poisoning is
unknown. RET was in Mexico at the
time, and the only amanita found where the poisonous
species was collected was brought to RET, he identified
the specimen (by microscopy) as Amanita
thiersii. It is important to know that
the mushroom was not from the material collected and
cooked by the poisoning victim. It was collected by
students who scoured the site after the poisoning was
A Wieland [Meixner] test on the
material involved in the cited poisoning case was
negative for amatoxins.
Given other (then recent)
poisonings by taxa of section Lepidella, I
considered that A. thiersii might contain
allenic norleucine. There was no evidence
and the symptoms of the poisoned person never became
RET's unjustified guess proved out to be wrong.
In recent years an
extensive study of large amino acids that are toxic
to humans was carried out—searching for these
amino acids in many amanitas. The experiment was
designed in part by RET in order to get broad coverage
of amanitas of every section of the genus then
recognized. Within section Lepidella
(sensu Bas 1969) we sampled at least one species of
every stirps to which we had access in the Roosevelt
herbarium and the herbaria of other
institutions. The results were very
informative and contradicted the
presumption of norleucine in
The individual study of A. thiersii showed
that it did not contain allenic norleucine.
At the time the A. ovoidea-A.
proxima-A. neoovoidea group
was incorrectly thought to belong
to section Amidella. This group is now
cited as belonging in the recently re-established section
Roanokenses for those following Cui et al.
In this group, at least
proxima contains allenic norleucine.
Unfortunately, the author of the study went out of
contact with RET and with his supervisor and the
results of the study have not been published.
RET has just been contacted by the supervisor (January,
2020). An attempt is being made to gather the
existing data and to carry out a repeat or an
of the experiments with a goal of publishing all
the relevant data.
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
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 industrial cellulose in
culture. The highest growth rate was recorded
for growth on sterilized grass clippings.
Genomic study: In 2009, a grant was received by the
that resulted in sequencing of the
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.
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 subsect.
Vittadiniae) that may serve as "genetic snap
shots" of the 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.
Bas (1969): [25/2/2] 7.5 - 9.5 × 7.0 - 9.0 μm, (Q = 1.0 - 1.10), colorless, hyaline, with very slightly thickened wall, amyloid, globose to subglobose; apiculus rather large, strongly projecting, broadly implanted; contents guttulate; color in deposit not recorded.
composite of data from all material revised by RET:
[70/4/4] (7.0-) 7.7 - 9.5 (-11.0) × (6.8-) 7.5 - 9.5
(-10.0) µm, (L = 8.1 - 8.7 µm; L’ =
8.4 µm; W = 7.8 - 8.2 µm; W’ = 8.0 µm;
Q = (1.0-) 1.01 - 1.10 (-1.17); Q = 1.04 -
1.07; Q’ = 1.05), hyaline, colorless, with
walls thin to slightly thickened, smooth, amyloid to
strongly amyloid, globose to subglobose, infrequently
broadly ellipsoid, adaxially flattened; apiculus
sublateral, predominantly cylindric,
occasionally truncate conic, often prominent,
occasionally proportionately narrow;
contents dominantly monoguttulate w/ or
without small granules, occasionally granular;
white in deposit.
Gregarious or in troops. On lawns, often in fairy rings. Occasionally fruiting with Chlorophyllum molybdites (Meyer : Fr.) Massee per J. McCandless, Louisville, Kentucky (pers. comm.).
Bas (1969): U.S.A.: TEXAS—Brazos Co. - College Station, 11.ix.1952 H. D. Thiers 1713 (holotype, MICH n.v.). 15.ix.1958 H. D. Thiers 5383 (paratype, L n.v.).
Wolfe et al. (2012)
vouchers for sequencing: KANSAS—?? Co. -
?? S. Kay 4041_het
MISSOURI—Cape Girardeua Co. - Cape
Girardeau, ca. Mississippi River bridge, 18.vii.2005
David P. Lewis, Pat Lewis & Bart Buyck [Lewis 7272] (FH).
PUEBLA—Mpio. Puebla - unkn. loc., 1.vii.1996 poisoning victim s.n. (MEXU).
ARKANSAS—Saline Co. - Bryant, 20-23.viii.1985 J. Justice s.n. [Tulloss 8-20/23-85-JJ1] (RET 205-6).
ILLINOIS—?? Co. - ??, ?? W. J. Sundberg ?? (SIU). Jasper Co. - Greenup, 1.viii.2003 Michael Kuo 08010305 (in herb. M. Kuo; RET 368-6).
KANSAS—Franklin Co. - Ottawa, Forest Pk., 419 N Locust St. [38°37'20" N/ 95°16'23" W, 272 m], 17.viii.2008 George Sayers s.n. (RET 424-9); Pomona, 2727 Colorado Rd. [38°34'53" N/ 95°27'06" W, 303 m], 8.ix.2008 George Sayers s.n. [Tulloss 9-10-08-B] (RET 423-3).
KENTUCKY—Jefferson Co. - Louisville, Cave Hill Cemetery [38°14'45" N/ 85°42'55" W, 151 m], 14.viii.1995 Judith McCandless s.n. (RET 156-3; TENN n.v.; VPI n.v.).
MARYLAND—Anne Arundel Co. - Baltimore-Washington International Airport [39°11'06" N/ 76°40;33" W, 35 m], 23.vi.2011 Ryoko Okamoto s.n. (RET 494-5, spore print and digital photo).
MISSISSIPPI—Washington Co. - Greenville, 20.viii.1982 Dan Guravich 1568 (MICH => BPI 751099); Greenville, St. Augustine, 18.viii.1972 Dan Guravich 140 (BPI 1104620).
MISSOURI—St. Louis - Tower Grove Pk. [38.6062° N/ 90.2553° W, 158 m], 3.ix.2012 Patrick Harvey s.n. [mushroomobserver.org #108503] (RET 513-7).
OKLAHOMA—?? Co. - ??.
TENNESSEE—Rutherford Co. - Smyrna Air Base [36.0024° N/ 86.513° W, 157 m], 8.ix.2012 Brian Adamo s.n. [mushroomobserver.org #109254] (RET 513-3).
TEXAS—Galveston Co. - Santa Fe, McCarvill’s residence, 6.viii.2000 David P. Lewis 6347 (RET 364-9). Jasper Co. - Jasper, off U.S. Rte 190 W, ca. Sergeant Jasper Motel [30°54'57" N/ 93°59'10" W, 77 m], 8.vi.1996 D. P. Lewis 5629 (RET 275-3). Jefferson Co. - Port Arthur, 21.ix.1976 D. P. Lewis 600 (in herb. David T. Jenkins n.v.; F n.v.; RET 028-2), 14.vi.1978 D. P. Lewis 1403 (F n.v.; RET 013-2), 26.vii.1978 D. P. Lewis 1485 (F n.v.; RET 028-1); Sabine Pass, Dick Dowling St. Pk., 11.ix.1999 D. P. Lewis 6205 (RET 364-10). Unkn. Co. - "E Texas," 25.x.1985 J. Justice s.n. [Tulloss 10-25-85-A] (RET 139-9).
[Note: there are also two collections at BPI.] [See also Guravich 1568 (MICH).]
—R. E. Tulloss
Information to support the viewer in reading the content of "technical" tabs
can be found here.
1. Amanita thiersii, Kansas, USA.
2. Amanita thiersii, Kansas, USA.
3. Amanita thiersii, Kansas, USA.
4. Amanita thiersii, Kansas, USA.
5. Amanita thiersii, Arkansas, USA.
6. Amanita thiersii, Kansas, USA.
7. Amanita thiersii, Kansas, USA.
8. Amanita thiersii spore germinating - courtesy Pringle Lab and Benjamin Wolfe
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.