Amanita muscaria
From Memory Alpha, the free Star Trek reference
Amanita muscaria is a fungus native to the subarctic climates of Earth. It is poisonous, and ingesting it can cause profuse sweating, convulsions and acute delirium. The Vikings knew it as the atuta, a powerful plant they boiled into broth and consumed before battle for spirit.
In 2371, The Doctor identified an Amanita muscaria to Freya in the Beowulf holodeck program. (VOY: "Heroes and Demons")
Amanita muscaria is known in English as the fly agaric or the fly mushroom. There is a common notion that Vikings used it to to induce their "berserker" rages, but there is little historical evidence for this.
