Amanita muscaria
Amanita muscaria was a fungus native to the sub-arctic climates of Earth, including Denmark. It was poisonous, and ingesting it could 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 the spirit of the bear.
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. [1]