"NO MUSHROOM is worthier of fear than the terribly poisonous Death Cap (Amanita phalloides). This single, widespread species of mushroom is solely responsible for the majority of fatal and otherwise serious mushroom poisoning cases, worldwide as well as in North America. Indeed, one might argue that the Death Cap's notorious, relatively frequent victimization of Homo sapiens is far and away the best explanation (or rationalization) for the widespread fear of edible wild mushrooms."
Amanita phalloides- The World's Most Dangerous Mushroom. Written and produced by David. W. Fischer     

Amanita phalloides, commonly known as the death cap, is a recent addition to our shores. It is a mycorrhizal fungus, often found growing in association with the roots of oak trees.

Like other Amanitas, A. phalloides has a sack-like volva around its base and an annulus, or skirt-like ring, around the top of it's stalk. The gills are white or cream and the spores are white. The cap is either slightly greenish yellow or white and is relatively clean, without the scattered articles that many of the other species of Amanita exhibit. As they age A. phalloides also exhibits a foul almost sickly-sweet smell.

A. phalloides is not indigenous to the United States. There is a debate over exactly how and when it arrived but many scientists believe that it was brought into the U.S. from Europe, carried among cork or oak tree seedlings imported into California, and has since adapted to our native oaks. In the area north of Rochester, New York it was first discovered in the 1970s under Norway spruce that had been imported as nursery stock decades earlier. It has since been found in increasing numbers, under oaks native to the New York area.