Nightshade

Not to be confused with the rank-smelling plant of the same name. The fungal cap from this rare and unusual mushroom may be either crushed or boiled into a tea. The mage must always use great care when handling nightshade, for it is not only a very potent hallucinogenic, it is also extremely poisonous. Adds illusion or poison.

Can only be found in Ultima IV in the deepest Spiritwood. Can be bought in later games. The Nightshade was screwed up in Ultima IX, where is was transformed into a leaf plant, which goes against everything known before about it.