Poisonous plants produce and accumulate poisons during vital activity; the plants are toxic to animals and humans. The principle active substances are alkaloids, glycosides (including saponins), essential oils, and organic acids. They are generally found in all parts of the plant, but frequently in different quantities.
Poisonous plants include many mushrooms, equisetics, club mosses, ferns, gymnosperms, angiosperms. In particular, poisonous berries abound. Hemlock and laburnum seed are noxious. In countries with temperate climates poisonous plants are most widely represented in the families: Ranunculaceae (crawfoot), Papaveraciae (poppy), Euphorbiaceae (spurges), Asclepiadaceae (milkweeds), Apocinaceae (dogbane), Solanaceae (nightshade), Scrophulariaceae (figwort), and Araceae (arum). Many plant poisons are valuable medicinal substances, for example, morphine, strychnine, atropine, and physostigmine.