This wild herb is thought to have caused the death of President Abraham Lincoln's mother. https://www.nps.gov/libo/learn/historyculture/milk-sickness.htm

When cattle eat White Snakeroot, their meat and milk become contaminated with the toxin Tremetol. If the meat or milk or meat is consumed by humans or calves, the poison is then passed on & can cause a serious condition called "milk sickness". During the early 19th Century, many thousands of settlers to the Midwest were killed by milk sickness.

However, Native Americans knew the deadly toxic effect of this herb. As with many herbs that can be poisonous, some Native Americans knew how to use it for medicinal purposes. Root tea was used to treat diarrhea, kidney stones, and fever. A root poultice can be used on snakebites. Thus, the name "snakeroot".

A Shawnee medicine woman passed on her knowledge on to a female, frontier doctor.

Having lost family members, the woman doctor then conducted her own experiments on cattle to scientifically determine toxicity of the plant. As a result, she discovered that white snake root (which blooms seasonally) was what was responsible for the death of her own mother & sister.

However because women doctors (actually women period) were not highly respected during her lifetime, the results of her experiments (and the knowledge passed on by the Shawnee Medicine Woman)were not accepted by the medical community until 55 years after the pioneer doctor's death.
Nevertheless, in 1928, the doctor's notes were finally published; thus revealing the cause of "milk fever".

Today, a domestic cultivar (deep burgundy leave) of White Snakeroot is planted in many flower gardens: https://www.saundersbrothers.com/plant/Eupatorium-rugosum-Chocolate This is also poisonous like the wild White Snakeroot.