The cap is 2.5 centimetres (1 inch) wide and hemispheric. The gills are adnate, crowded, medium broad, entire, white, unchanging.
The stem is about 30 by 5–8 millimetres (1+1⁄8 in × 1⁄4 in–3⁄8 in), narrowing upward, smooth, glabrous, white, unchanging when bruised. The ring is fixed 10 mm (3⁄8 in) from the top of the stem, very short, skirt-like, grooved by the gills above, white, persistent. The bulb is ovoid, white, 20 mm × 15 mm (3⁄4 in × 5⁄8 in). The volva is neither appressed nor widely spreading, the edge is either 3-lobed or ragged.[2] The mushroom is odorless and tasteless.
Similar species
A. hygroscopia resembles several edible species, most notably Agaricus campestris.
Toxicity
The principal toxic constituent is α-Amanitin, an elective inhibitor of RNA polymerase II and III, which causes liver and kidney failure. 15% of those poisoned will die within 10 days and those who survive are at risk of lifelong, permanent liver damage.[3]
There is no antidote for amanitin poisoning; treatment is mainly supportive (gastric lavage, activated carbon, and fluid resuscitation). In severe cases the only effective treatment may be a liver transplant.
Amatoxins, the class of toxins found in these mushrooms, are thermostable: they resist changes due to heat, so their toxic effects are not reduced by cooking.
^Benjamin, Denis R. (1995). "Amatoxin syndrome". Mushrooms: Poisons and Panaceas – A Handbook for Naturalists, Mycologists and Physicians. New York: W. H. Freeman and Company. pp. 198–214.
