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Top 10 Most Poisonous Plants

White Snakeroot

Most people know that John Wilkes Booth assassinated Abraham Lincoln, but did you know that a plant killed the president's mother? The culprit: white snakeroot (Eupatorium rugosum), a shade-loving weed native to the forests of the eastern and southern United States. This shrubby plant grows to a height of 18 to 60 inches (46 to 152 centimeters) and boasts leaves that are serrated around the edges. Its flowers, which emerge from the ends of the branches in late summer, are small and grow in white clusters. Don't let these beautiful blooms fool you, though; the plant contains high levels of tremetol, a powerful toxin.

White snakeroot causes "milk sickness," a condition that afflicts people who consume milk or meat from a cow that has grazed on the highly poisonous plant. (Snakeroot is also poisonous to the cow.) Those affected can experience a variety of symptoms, including bad breath, loss of appetite, listlessness, weakness, vague pains, muscle stiffness, vomiting, abdominal discomfort, severe constipation, coma and possibly death. Milk sickness was common until the 1920s when farmers widely recognized white snakeroot as the cause, eradicating the weed from their pastures and fencing them to prevent cows from wandering into the woods to graze. Unfortunately, this discovery came much too late for Lincoln's mother, Nancy, who fought milk sickness for two weeks before passing away on Oct. 5, 1818.