Ageratina altissima-White Snakeroot

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

White Snakeroot, Richweed, White Sanicle

Ageratina altissima

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Synonyms of Ageratina altissima from Plants of the World Online (21 as of 1-8-20): Ageratina ageratoides Spach, Ageratum altissimum L., Batschia nivea Moench, Eupatorium aboriginum Greene, Eupatorium ageratoides L.f., Eupatorium ageratoides var. angustatum A.Gray, Eupatorium altissimum (L.) L., Eupatorium boreale Greene, Eupatorium eurybiifolium Greene, 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 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.
Accepted infraspecific name: Ageratina altissima var. angustata (A.Gray) Clewell & Wooten

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.

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. According to Plants of the World Online by Kew (as of 10-20-18), there are 322 accepted species in the genus Ageratina.


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.

The 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 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) produce 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. 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 horticulturalist 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. 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.