White Snakeroot – The Plant that Killed Abe Lincoln’s Mother

By Kimberlee Carey

I was first introduced to white snakeroot (Ageratina altissima) during a 4-H pasture management seminar, “Danger in the Grass:  Plants Toxic to Horses” (https://extension.psu.edu/toxic-plants-in-horse-pastures).  First, we watched a video, and then club members and volunteers gathered live plant samples for a hands-on identification activity.  This session sparked my curiosity, so I continued to scout the area near my home, identifying toxic plants and marking their locations.  It was late summer when I spied white snakeroot peeking out from a wooded area just above a soybean field.  Even though I knew they were poisonous, I still thought that the plants were stunning!

White snakeroot is a perennial herb native to North America.  It is a member of the aster family.  “Aster” is Latin for “star,” and refers to the shape of the flower head.  Along with its cousin, goldenrod (Solidago spp.), white snakeroot is one of the few native plants that are still flowering at the end of the growing season.  This is truly a blessing for many pollinators such as flies, bees, and moths.  White snakeroot flowers provide vital nectar and pollen just before the first killing frost destroys this food source.

White snakeroot is easily identified by clusters of showy white flowers, which begin blooming in July.  The leaves are opposite, coarsely toothed, and rounded at the base.  Each leaf has a sharply-pointed tip.  White snakeroot can reach a height of three feet.  It thrives in moist, shady areas along meadows, thickets, fields, and woodlots.  The plant spreads by producing wind-blown seeds and rhizomes (horizontal underground stems), allowing it to colonize quickly in preferred soil conditions.  White snakeroot is a welcome addition to many pollinator gardens and landscapes.  It is often seen in mass plantings or naturalized borders.

Having discussed the merits of white snakeroot, let us dig into this plant’s lethal history.  The leaves and the stems of white snakeroot are extremely poisonous.  This is due to the toxin tremetol, an unsaturated alcohol with a consistency and odor resembling turpentine.  The toxin is more potent in fresh green plants, but can remain, to a lesser degree, even after a hard frost.  According to the Ohio Weed Guide (https://www.oardc.ohio-state.edu/weedguide/single_weed.php?id=91), “dried [white snakeroot] plants in hay are toxic but not as poisonous as fresh plants.”

 If grazing areas for cattle and horses have inadequate grass cover, livestock will resort to eating any available plants, including white snakeroot.  Once consumed, cattle and horses alike will show signs of weakness, loss of appetite, seizures, and pronounced trembling, often leading to death.  In addition, lactating cows can pass the tainted milk on to both calves and humans, causing severe lethargy, tremors, vomiting, delirium, and eventually death.  This is how the disease became known as “milk sickness.”  Please be aware that tremetol levels in the meat of animals that died of milk sickness can also be toxic to humans.

In the early eighteen hundreds, milk sickness claimed thousands of lives.  It wasn’t uncommon for entire families to die of the disease.  The most notable victim was Nancy Hanks Lincoln, Abraham Lincoln’s mother.  She is thought to have succumbed to milk sickness during the summer of 1818, leaving behind young Abe and his sister, Sarah.  Tragically, Mrs. Lincoln was not alone, as many other people in Little Pigeon Creek, Indiana, died in the same outbreak of this disease.  

Eventually, a frontier physician, Dr. Anna Pierce Hobbs Bixby, learned of the cause of milk sickness from a woman of the indigenous Shawnee people.  The woman helped Dr. Anna (as she was called by her patients) identify the plant, and warned her of its toxic properties.  Dr. Anna then experimented by feeding the stems and leaves from white snakeroot plants to a calf.  It wasn’t long before it displayed the familiar symptoms of “the trembles,” and the calf soon died.  Following the results of her experiment, Dr. Anna led a campaign to remove white snakeroot from local grazing lands, and almost eliminated the disease from her village of Rock Creek, Illinois.  Although others also obtained the same results, medical society largely ignored Dr. Anna’s findings.  Regrettably, milk sickness continued to claim thousands of lives until the early nineteen hundreds.  After years of research, scientists finally confirmed that tremetol from white snakeroot was, indeed, the primary cause of milk sickness.   

Milk sickness, thankfully, is no longer as great a concern for commercial dairy operations.  This is largely due to education and better pasture management.  In addition, milk from many dairy farms is mixed together at processing plants, diluting any tremetol that is present.  It is always good practice, however, to find and eliminate toxic plants in livestock grazing areas.  As the saying goes, “an ounce of prevention is worth a pound of cure.”

Despite it dark history, is the bee-friendly white snakeroot a friend or foe?  I guess it literally depends on which side of the fence you are standing.  In any case, do not eat white snakeroot; leave it for the pollinators!

Kimberlee Carey has been a Penn State Master Gardener Apprentice since April, 2020.  She can be reached at clintonmg@psu.edu or through the Clinton County Master Gardener Hotline at (570) 858-0198.