(L.) King & H.E.Robins.
Ageratina altissima, also known as white snakeroot, richweed, white sanicle, or tall boneset, is a poisonous perennial herb in the family Asteraceae, native to eastern and central North America. An older binomial name for this species is Eupatorium rugosum, but the genus Eupatorium has undergone taxonomic revision by botanists and a number of the species once included there have been moved to other genera.
Plants are upright or sometimes ascending, growing to 1.5 meters tall, producing single or multi-stemmed clumps. They are found in woods and brush thickets where they bloom mid to late summer or fall. The flowers are a clean white color and after blooming, small seeds with fluffy white tails are released to blow in the wind. This species is adaptive to different growing conditions and can be found in open shady areas with open bare ground; it can be weedy in shady landscapes and in hedgerows. There are two different varieties Ageratina altissima var. angustata and Ageratina altissima var. roanensis (Appalachian white snakeroot); they differ in the length of the flower phyllaries and shape of the apices.
White snakeroot contains the toxin tremetol; when the plants are consumed by cattle, the meat and milk become contaminated with the toxin. When milk or meat containing the toxin is consumed, the poison is passed on to humans. If consumed in large enough quantities, it can cause tremetol poisoning in humans. The poisoning is also called milk sickness, as humans often ingested the toxin by drinking the milk of cows that had eaten snakeroot.
During the early 19th century, when large numbers of European Americans from the East, who were unfamiliar with snakeroot, began settling in the plant's habitat of the Midwest and Upper South, many thousands were killed by milk sickness. Notably, milk sickness was possibly the cause of death in 1818 of Nancy Hanks Lincoln, mother of Abraham Lincoln.
It was some decades before European Americans traced the cause to snakeroot, although today Dr. Anna Pierce Hobbs Bixby is credited with identifying the plant in the 1830s. Legend has it that she was taught about the plant's properties by a Shawnee woman. The Shawnee woman's name is lost to history, but she and her people would have had deep knowledge of the herbs and plants in the area.
The plants are also poisonous to horses, goats, and sheep. Signs of poisoning in these animals include depression and lethargy, placement of hind feet close together (horses, goats, cattle) or held far apart (sheep), nasal discharge, excessive salivation, arched body posture, and rapid or difficult breathing.
A cultivar, sold under the name Eupatorium rugosum 'Chocolate', is grown in gardens for its dark-tinted foliage. The darkest color, which is a chocolaty black, occurs in plants grown in a sunny location. The plants are shade-tolerant and do best in moist soils. More recently, the plant can be found under the correct species name.
- "The Plant List: A Working List of All Plant Species".
- "USDA GRIN Taxonomy".
- "Ageratina altissima (Linnaeus) R. M. King & H. Robinson var. roanensis (Small) Clewell & Wooten". Flora of North America.
- "Ageratina altissima (Linnaeus) R. M. King & H. Robinson var. altissima". Flora of North America.
- "Milk Sickness", National Park Service
- W. D. Snively, Minnesota Medicine, V. 50, April 1967, pp. 469-476
- John W. Allen, It Happened in Southern Illinois, Carbondale: Southern Illinois University Press, 1968 (reprint, paperback, 2010 - Googlebook version), pp. 5-6, accessed 1 July 2011
- "Medicinal Plants-White Snakeroot". Bio.brandeis.edu. Retrieved 2013-11-05.
- "Eupatorium rugosum 'Chocolate'". Missouri Botanical Garden.
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