Some of the most poisonous plants in the world include water hemlock, deadly nightshade, white snakeroot and the rosary pea. Many of these and other poisonous plants are native to tropical areas, such as South America and Africa.
Many of these plants are lethal when eaten, but that doesn't mean that the plant must be consumed for the negative effects to take place. For example, a single seed of the rosary pea, if broken or scratched, releases more than enough deadly protein to kill an adult. Oleander is a similar plant, with a poisonous sap that severely irritates the skin, at the very minimum.