Castor oil plant (Ricinus communis) from Maria Sibylla’s Metamorphosis Insectorum Surinamensium.
In 2007 edition of Guinness World Records the castor oil plant was named the most poisonous plant in the world. Just 4-8 seeds are enough to kill a grown person. The toxicity of this plant is due to the ricin it contains. Ricin is a chemical compound that inhibits ribosomes in the cells. As ribosomes are the molecules which produce proteins in the cells, once ricin interacts with ribosomes the protein production stops and it eventually kills the cell.
Extracts of castor oil plant have been widely used both as medicine and as poison. Under the 1972 Biological Weapons Convention ricin is marked as a schedule 1 controlled substance. Over the course of history ricin has been considered for use as a biological weapon as a part of bombs and bullets. In medicine ricin has been used in experiments involving cancer tumor treatment and improvement of vaccine immunogenicity.