Most poisonous (common) plant
Castor Bean
United States ()

Based on the amount it takes to kill a human, the most poisonous common plant in the world is the castor bean (Ricinus communis). According to the Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (1997) a dose of 70 micrograms (2 millionths of an ounce) is enough to kill a person weighing 72 kg (160 lb or 11 st 4 lb).