20 of the World's Deadliest Plants

Aconitum (aka monkshood, wolfsbane, and devil's helmet)
The poisonous properties of members of the Aconitum genus have been known for generations; several species of the plant, for example, have long been used in preparing poison-tipped arrows for purposes of hunting and warfare. In humans, accidental ingestion can be fatal; the plants contains appropriately named aconitine neurotoxins and cardiotoxins, which lead to gastrointestinal complications, motor weakness, and heart and lung paralysis.