20 of the World's Deadliest Plants

 Ageratina altissima (aka White Snakeroot)
White snakeroot is so potent that just drinking the milk or eating the meat of a cow that's ingested the plant can lead to severe sickness and even death. The plant contains a toxin called tremetol, which, when ingested by humans, can lead to trembling, vomiting, and serious intestinal troubles. The illness brought on by secondary tremetol ingestion was so widespread in the early 19th century that it became known as "milk sickness," and is estimated to be responsible for thousands of deaths at the time — including that of Abraham Lincoln's mother, Nancy Hanks Lincoln.