Ageratina altissima-White Snakeroot

Ageratina altissima (White Snakeroot) on 9-6-18, #503-1.

White Snakeroot, Richweed, White Sanicle

Ageratina altissima

ad-jur-uh-TY (TEE)-nuh  al-TISS-ih-muh

Synonyms of Ageratina altissima from Plants of the World Online (23 as of 3-21-21): Ageratina ageratoides Spach, Ageratum altissimum L., Batschia nivea Moench, Eupatorium aboriginum Greene, Eupatorium ageratoides L.f., Eupatorium altissimum (L.) L., Eupatorium boreale Greene, Eupatorium cordatum var. fraseri (Poir.) DC., Eupatorium eurybiifolium Greene, Eupatorium fraseri Poir., Eupatorium frasieri Poir., Eupatorium odoratum Walter, Eupatorium rugosum Houtt., Eupatorium rugosum var. chlorolepis Fernald, Eupatorium rugosum var. tomentellum (B.L.Rob.) S.F.Blake, Eupatorium rugosum f. villicaule (Fernald) Fernald, Eupatorium rugosum var. villicaule (Fernald) S.F.Blake, Eupatorium urticifolium Reichard, Eupatorium urticifolium var. tomentellum B.L.Rob., Eupatorium urticifolium var. villicaule Fernald, Kyrstenia aborginum Greene, Kyrstenia altissima (L.) Greene, Kyrstenia borealis Greene

Ageratina altissima (L.) R.M.King & H.Rob. is the correct and accepted name for this species of Ageratina. It was named and described as such by Robert Merrill King and Harold Ernest Robinson in Phytologia in 1970. It was described as Ageratum altissimum by Carl von Linnaeus in the second edition of Species Plantarum in 1753.

Accepted infraspecific name: Ageratina altissima var. angustata (A.Gray) Clewell & Wooten

A few cultivars of this plant have been available for home gardens and often sold under the species name Eupatorium rugosum, which is now a synonym. 

The genus, Ageratina Spach, was named and described by Édouard Spach in Histoire Naturelle des Végétaux in 1841.

Plants of the World Online by Kew lists 325 accepted species in the Ageratina genus (as of 3-21-21 when I last updated this page. It is a member of the plant family Asteraceae with 1,679 genera. Those numbers could change as updates are made.

Distribution map of Ageratina altissima from Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; Retrieved on 3-21-21.

The above distribution map for Ageratina altissima is from Plants of the World Online. Areas in green are where the species is native and purple where it has been introduced. The map on the USDA Plants Database for North America is the same. The species could have a wider range than what the maps show.


Ageratina altissima (White Snakeroot) on 9-6-18, #504-1.

There are individual small groups here and there on the farm but several very large groups as well. They have nice “Ageratum-like” flowers. Like many wildflowers, however, it is a poisonous weed.

Ageratina altissima (White Snakeroot) on 9-6-18, #513-1.

The White Snakeroot can be found in pastures, along roadsides, edges of and in woodlands, brushy thickets, etc. This adaptable plant can grow as a single stem or multi-stemmed clumps, singly or in colonies. The plants have bright white flowers which produce small seeds with fluffy tails that blow in the wind.

Ageratina altissima (White Snakeroot) on 9-6-18, #513-2.

Wikipedia says, “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.” 

Thousands of settlers died in the early 19th century in the US from milk sickness from these plants. Although Dr. Anna Pierce Hobbs Bixby is credited with identifying the plant in the 1830s, legend has it she was taught about the plant by a Shawnee woman.

Ageratina altissima (White Snakeroot) on 9-6-18, #513-3.

Ageratina altissima leaves are opposite, petiolate, and simple. In shape, they are triangular to triangular-ovate, sharply pointed with broadly toothed margins, slightly hairy with three main veins. The three veins have been a good way to identify this plant, especially when it isn’t flowering.

Their main flower head (inflorescence) produces from 9-25 flowers (florets) with 5 petals (corollas).

Ageratina altissima (White Snakeroot) on 9-6-18, #515-1.

Family: Asteraceae
Origin: North America
Zones: USDA Zones 3-8 (° F)
Size: 3-5 feet tall x 2-4 feet wide
Light: Full sun to part shade
Water: Medium to wet
Blooming Period: Summer through frost

Ageratina altissimum (White Snakeroot) on 8-7-19, #612-1.

I found a few Ageratina altissima growing in the back of the farm in a mostly shady area on August 7 (2019). Right next to it was a plant that was the same species with more elongated leaves. Check the veins on the leaves for proper ID.

Ageratina altissimum (White Snakeroot) on 8-7-19, #612-2.

The genus name, Ageratina, means “Ageratum-like”. If you have grown Ageratum in your flower bed, you can see why. Conoclinum coelestinum grows in the wild in some areas, which is the Blue Mistflower or Hardy Ageratum with blue flowers. There are several white cultivars available as well.

Ageratina altissimum (White Snakeroot) on 8-7-19, #612-3.

Although the White Snakeroot may be a neat-looking plant and there are cultivars available, I think it is best left in the wild. Definitely not one you would want to use in a salad.

Ageratina altissimum (White Snakeroot) on 8-7-19, #612-4.

Be sure to check the links below for accurate and technical descriptions.

Ageratina altissimum (White Snakeroot) on 8-7-19, #612-5. says Ageratina altissima is often confused with Eupatorium serotinum which is taller and less branched. Eupatorium serotinum leaves are also more lanceolate (lance-shaped). Flowers are said to be dirtier looking than Ageratina altissima. What can be confusing is that there is both  Ageratina altissima and Eupatorium altissimum which is somewhat confusing. Eupatorium altissimum (L.) L. is a synonym of Ageratina altissima (L.) R.M.King & H.Rob. but Eupatorium altissimum L. is an accepted species. Apparently, Mr. Linnaeus gave two different plants the same name… Hmmm… So, he initially named two different species Ageratum altissumum but was correct about Eupatorium altissimum, which one of the incorrectly named species was also, which he incorrectly renamed the second time around.

Many scientific names have been changing because so many plants have had multiple scientific names. Botanists and horticulturalists are working hard to straighten the mess out so we must be patient and understanding.

I have enjoyed photographing and learning about the many wildflowers growing on the farm and other areas. My farm is in Windsor, Missouri in Pettis County (Henry County is across the street and Benton and Johnson aren’t far away). I have grown over 500 different plants and most have pages listed on the right side of the blog. I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can be somewhat variable from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at I would enjoy hearing from you especially if you notice something is a bit whacky. 


NOTE: The figures may not match on these websites. It depends on when and how they make updates and when their sources make updates (and if they update their sources or even read what they say). Some websites have hundreds and even many thousands of species to keep up with. Accepted scientific names change periodically and it can be hard to keep with as well. In my opinion, Plants of the World Online by Kew is the most reliable and up-to-date plant database and they make updates on a regular basis. I make updates at least once a year and when I write new pages but I do get behind. We are all a work in progress. 🙂


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