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 (8) (Updated on 11-29-23 from Plants of the World Online): Ageratina ageratoides Spach, Ageratum altissimum L., Batschia nivea Moench, Eupatorium ageratoides L.f., Eupatorium altissimum (L.) L., Eupatorium rugosum Houtt., Eupatorium urticifolium Reichard, Kyrstenia altissima (L.) Greene
Synonyms for Ageratina altissima var. altissima (15) Updated on 11-29-23 from POWO): Eupatorium aboriginum Greene, Eupatorium boreale Greene, Eupatorium cordatum var. fraseri (Poir.) DC., Eupatorium eurybiifolium Greene, Eupatorium fraseri Poir., Eupatorium frasieri Poir., Eupatorium odoratum Walter, 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 var. tomentellum B.L.Rob., Eupatorium urticifolium var. villicaule Fernald, Kyrstenia aborginum Greene, Kyrstenia borealis Greene
Synonyms of Ageratina altissima var. angustata (5) (Updated on 11-29-23 from POWO): Eupatorium ageratoides var. angustatum A.Gray, Eupatorium angustatum Greene, Eupatorium rugosum var. angustatum (A.Gray) S.F.Blake, Eupatorium urticifolium var. angustatum (A.Gray) B.L.Rob., Kyrstenia angustata Greene

Ageratina altissima (L.) R.M.King & H.Rob. is the accepted scientific 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 Names: *Ageratina altissima var. altissima (autonym), Ageratina altissima var. angustata (A.Gray) Clewell & Wooten. *When an infraspecific taxon is named, an autonym (“type-specimen”) is automatically generated whose description is closest to the (original) species. All have their own list of synonyms… 

A few cultivars of this plant have been available for home gardens and are 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.

As of 11-29-23 when this page was last updated, Plants of the World Online by Kew lists 315 accepted species in the Ageratina genus. It is a member of the plant family Asteraceae with 1,702 genera. Those numbers could change as updates are made on POWO. The number of genera in the family fluctuates often… 

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 is where it has been introduced. The map on the USDA Plants Database for the United States and Canada is the same. Flora of North America includes Saskatchewan but not the Northwest Territories. The species could have a wider range than what the maps show. Both lower taxon are found in Missouri where I live.

The map on iNaturalist shows where members have made observations. Anyone can join and it is a great website to confirm and share your observations. The maps on iNaturalist are continually updated as members post new observations.

THERE ARE A FEW LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING AND BETTER PLANT ID.

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.

There are more photos at the bottom of the page.

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.

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 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).

USEFUL INFORMATION:
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

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.

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.

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.

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

The Missouri Plants website 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 are both  Ageratina altissima and Eupatorium altissimum. 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…

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 live on a small farm in Windsor, Missouri where I enjoy gardening, collecting plants, and identifying wildflowers. The farm is in Pettis County but Henry County is across the street, and Benton and Johnson aren’t far away. I have grown over 500 different plants and identified over 250 wildflowers (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 thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky. 

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
FLORA OF NORTH AMERICA (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
MISSOURI BOTANICAL GARDEN
DAVE’S GARDEN
MISSOURI PLANTS
MSU-MIDWEST WEEDS AND WILDFLOWERS
USDA PLANTS DATABASE
iNATURALIST
ILLINOIS WILDFLOWERS
MINNESOTA WILDFLOWERS
LADY BIRD JOHNSON WILDFLOWER CENTER
KANSAS WILDFLOWERS AND GRASSES
WILDFLOWER SEARCH
BROOKLYN BOTANIC GARDEN
PFAF (PLANTS FOR A FUTURE)
GO BOTANY
MARYLAND BIODIVERSITY PROJECT

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. 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. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is one of the most reliable and up-to-date plant databases and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos but I do get behind. We are all a work in progress. 🙂

More photos from 2019…

 

 

 

 

 

Photo from 2021…

Photos from 2023…