Death Cap
The death cap is responsible for the majority of fatal mushroom poisonings worldwide and is now well established in North America, especially along the West Coast and Northeast, where it partners with oaks and introduced hardwoods in parks and gardens. It is a medium to large mushroom with a smooth, greenish to yellowish or pale olive cap, white gills, a white ring on the stem, and — the critical feature — a membranous cup (volva) around a swollen stem base that is often buried and easily missed.
Every serious identification of a pale gilled woodland mushroom must include excavating the stem base to check for that cup. In its young egg stage it can be mistaken for an edible puffball (a lengthwise slice reveals the developing capped mushroom inside), and the mature form has been confused with edible pale-capped mushrooms and the paddy-straw mushroom. Its toxins (amatoxins) are not destroyed by cooking and cause delayed liver and kidney failure. In the garden, know it, teach children to leave it, and keep pets away.
Deadly
Deadly — its amatoxins are not destroyed by cooking and cause delayed, often fatal liver and kidney failure. Confused in its white egg stage with edible puffballs, and mature specimens with pale edible mushrooms and the paddy-straw mushroom. The decisive checks: slice any white ball lengthwise (a death cap button shows a developing cap and gills; a puffball is featureless white), and excavate the stem base to expose the cup-like volva that edible meadow mushrooms lack.
Giant puffball and other puffballs (Calvatia, Lycoperdon) in the egg stage, Meadow mushroom (Agaricus campestris), Paddy-straw mushroom (Volvariella volvacea)
Forms mycorrhizal partnerships with oaks and introduced hardwoods, so ecologically it supports tree roots. Its significance to a gardener, however, is entirely as the deadliest mushroom likely to appear in a lawn or park.
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