The Friends of the Wild Flower Garden, Inc.

Plants of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States


Common Name
White Snakeroot


Scientific Name
Ageratina altissima (L.) R.M.King & H. Robinson var. altissima


Plant Family
Aster (Asteraceae)

Garden Location
Woodland & Upland


Prime Season
Late Summer to Early Autumn



White Snakeroot is a native erect perennial forb growing 1 to 3 feet high on greenish stems that are mostly hairless but can have minute fine hairs. Some branching occurs both below and within the floral array.

Leaves are egg shaped to lanceolate, up to 5x as long as wide, with a long tapered tip, rounded base, oppositely arranged, coarsely toothed and on a long stalk (over 3/4 inch). Lower leaves may have a heart-shaped base. Upper stem leaves are more lanceolate with a tapered base to the stalk. Upper leaf surfaces are usually hairless, the underside is paler in color and can have whitish hair on the ribs. Some stem leaves near the floral array may have an alternate arrangement instead of opposite.

The floral array is composed of terminal roundish branched clusters (corymbs) on the upper stems, some of which spring from the leaf axils.

Flowers: Each flower cluster is up to 1/2 inch wide when mature and composed of 10 to 30+ flower heads. Each head has a variable number of tubular florets that have 5-parted white corollas with lips that are pointed and spreading when the flower opens. The five stamens with yellow anthers cluster around the base of the style which has a forked stigma and greatly exceeds the length of the corolla. Ray florets are absent. Surrounding the outside of the flowerhead is a series of green phyllaries with pointed tips. The flower heads in each cluster have stalks of varying length so that the top of the cluster appears flat to rounded.

Seed: Fertile florets produce a dark dry oblong 5-ribbed obconic shaped cypsela (like an achene) that has tuffs of fluffy pappus for wind dispersion. Seeds require at least 60 days of cold stratification and then light for germination.

Varieties: There are two varieties - var. altissima and var. roanensis. The difference is in the shape of the tips of the phyllaries of the flowerhead. Only the former is found in Minnesota. It has phyllaries 3 to 5 mm long with tips that are not cuspidate (abruptly tapered to a point). The second variety has phyllaries 4 to 7 mm long with tips cuspidate to acuminate

Toxic - Which Snakeroot causes the trembles in cattle and milk sickness in humans - see bottom of page for details.


Habitat: White Snakeroot normally grows in partial shade in disturbed sites, woodland and path edges in various soils as long as the moisture level is moist to mesic. It has a rhizomatous root system which allows vegetative growth and it will easily self-seed along the edges of a woodland or spread via the root system.

Names: The genus Ageratina is derived from the Greek ageratos, which was used in botanical language for plants that kept their color for a long time - hence the Ageratums. The Latin suffix ina made it 'small Ageratum', in this case a small flowered one. The species altissima means 'tallest' or 'very tall' - a tall Ageratina. The scientific name for the plant has been recently revised with the plant moved into the genus Ageratina but a number of references will still use an older name of Eupatorium rugosum which was once assigned to this variety but is no longer accepted. An even older name for this variety, current in Eloise Butler's day but again, no longer accepted, was Eupatorium urticifolium.

The old species name, rugosum, means "rough" and the older genus name, Eupatorium, is much more fun to read about. It was named after Mithridates Eupator the ruler of Pontus in old Asia Minor, who lived from 135-63 BC. He was the sixth in his line and was aware that the principal method of disposing of ones enemies in those days was by poison so he began using plants in his medicine and in his personal quest to become insensitive to poisons. By ingesting a slight amount of plant poisons each day along with various plant based antidotes, Mithridates was able to build an immunity to many poisons, such that when he wished to commit suicide following his defeat, poison would no longer work and he had to have a military associate slay him by the sword. Long a friend of Rome, he had gone his own way, defeating two prominent Roman generals in the process, but in 63 BC he was finally defeated in his own kingdom of Pontus by Gnaeus Pompeius Magnus, which battle earned Pompey the title “Pompey the Great,” who then was later associated with Julius Caesar in the First Triumvirate.

The common name of 'snakeroot' was due to a misconception by the early settlers that the root of the plant was useful for treating snakebite.

The author names for the plant classification are: The first to classify in 1753 using the name Ageratum altissimum was '(L)' which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was updated in 1970 by ‘R.M.King’ who is Robert Merrill King (1930-2007) American botanist, research associate at the Smithsonian and at the Missouri Botanical Garden and frequent collaborator with 'H.Robinson' who is Harold E. Robinson (1932 -) American botanist, specialist in the Asteraceae.

Comparisons: There are only a few plants with white corymb flower clusters that might be confused. The closest is Boneset, Eupatorium perfoliatum L., but there the leaves are a different shape and pierce the stem, and that plant is located in sunny moist areas.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

floral array flower closeup

Above: The floral array is composed of terminal roundish branched clusters of flowerheads (corymbs) on the upper stems. Individual florets in each flowerhead have a white corolla with 5 pointed, spreading lips from which is exserted a long style with divided tip. Florets open from the outer edge of the head first.

Blooms occur from late-July to mid-September depending on seasonal weather.

White Snakeroot White snakeroot

Below: The large opposite leaves have coarse teeth, a rounded to heart-shaped base to the stalk and taper to a pointed tip.

White Snakeroot White Snakeroot Leaf

Below: 1st photo - The green linear phyllaries around the flower head have pointed tips. 2nd photo - A large group of White Snakeroot. The rhizomatous root system allows colonies to from.

flower heads group of plants

Below: An upper stem leaf, smaller, less egg-shaped and with smaller and fewer marginal teeth.

upper stem leaf

Below: 1st photo - the underside of the leaf is paler in color and has fine whitish hair on the ribs. 2nd photo - A stem section - greenish, usually smooth, except there can be minute whitish hair as seen here.

Leaf underside Stem section

Below: Seeds are a dark oblong dry cypsela with fluffy white pappus attached for wind dispersion.

seed head seed
Plant group


Notes: White Snakeroot is indigenous to the Garden area. Eloise Butler catalogued it on Sept. 6, 1907 using the older name for this variety of Eupatorium urticifolium that was accepted in her day. There is no record that she or her successors ever had to replant it. It is native to most counties in Minnesota except the north third and a few in the far SW corner. In North America it is found from the central plains eastward in the U.S. and from Ontario eastward in Canada except the Maritime Provinces. This is the only species of Ageratina found in Minnesota.

Toxicity and Medicinal notes: White Snakeroot has poisonous characteristics as it contains trematol, a toxic alcohol, which causes Ketosis. If cows eat enough of the plant they get a disease called 'the trembles' which eventually leads to death but if they are lactating, the toxin is secreted into the milk causing milk sickness in those who drink the milk. Abe Lincoln's mother, Nancy Hanks Lincoln, died of the disease in 1818 (When young Abe was 7 years old) at Little Pigeon Creek, Indiana. Because of the prevalence of the disease in the area, Thomas Lincoln and his new wife then moved to Illinois where Lincoln grew up.

The link between this plant and milk sickness was made by Illinois doctor (although trained only as a nurse and midwife) Anna Pierce in the 1830s after she had lost a number of family members to the toxin and found she had no way to cure it. She had befriended a Shawnee woman known as Auntie Shawnee, who was a fugitive from the Shawnee re-location. The woman took Dr. Pierce into the woods and showed her the plant. See experimented with feeding the plant to a calf which then developed the 'trembles', confirming the link. Her work was not believed, but several other doctors performed their own experiments and came to the same conclusion but the mainstays of the medical profession would hear nothing of it.

It was not until 1928 when Dr. James Couch isolated the chemicals that belief finally set in. It was determined that the constituents of Snakeroot are not in themselves poisonous but when the human body metabolizes them, they are converted into toxic substances. It has also been determined that the concentration of chemicals in the plant varies regionally and by the amount of seasonal moisture. In humans, milk sickness has progressive symptoms: Lassitude, a sickly sweet breath, nausea, vomiting, stomach pains, intense thirst, prostration, coma, death. (For a complete discussion see Natural History, July 1990, "Land of Milk and Honey" by David Duffy Cameron).

Eloise Butler wrote of this plant: "The most beautiful of the eupatoriums is the White Snakeroot, also of medicinal repute. It is of value not only on account of its profuse, soft, starry inflorescence of harmonious white, but because it is easily cultivated and can be depended upon to bloom after frosts have set in. In one garden at least in Minneapolis, besides the wild one, where it stars the ground in late summer, it is the most prized ornament. The flowers yield not a whit in beauty to those of the ageratum, which they resemble so much in form that they once bore the name ageratoides - meaning like ageratum." Published Aug. 6, 1911, Minneapolis Sunday Tribune. Eloise would be interested to know that the species is now moved back to a genus referring to Ageratums - Ageratina.

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

graphicIdentification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.