White Snakeroot

Photo of white snakeroot leaves and flowers
Safety Concerns
Scientific Name
Ageratina altissima (formerly Eupatorium rugosum)
Asteraceae (daisies)

White snakeroot looks very similar to the thoroughworts and bonesets, but it has triangular leaf blades that are more broadly angled or rounded at the base (not as narrow/lanceolate as in the thoroughworts). White snakeroot is common statewide. It’s a toxic plant if eaten, so it’s good to be able to identify it.

White snakeroot is an upright, much-branched perennial with smooth (sometimes hairy) stems and fibrous roots. The flowerheads are arranged in loose, terminal, flat-topped clusters. The flowers point upward and are clear white and tuftlike. Bracts of the involucre (leafy appendages at the base of the flowerhead) are acutely pointed and hairless. Blooms July–October. Leaves opposite, broadly ovate, with long petioles (leaf stems) and large teeth.

Similar species: White snakeroot used to be placed in genus Eupatorium (thoroughworts or bonesets), and nine species in that genus have been recorded in Missouri. All have rather similar clusters of fuzzy-looking white flowers. Because white snakeroot is toxic if eaten, it is good to know how to tell these plants apart. Leaf characteristics are usually the best way to distinguish between them. One common and widespread thoroughwort, late boneset (Eupatorium serotinum) has leaf blades that are somewhat narrower, with a more narrowly angled leaf bases. It also typically has grayish flowers instead of white or greenish white.


Height: to 4 or 5 feet.

Where To Find
image of White Snakeroot distribution map


Occurs in rich or rocky woods, bottomland forests, bases and ledges of bluffs, clearings, banks of streams and rivers, pastures, old fields, roadsides, waste places and other open, disturbed areas.

Native wildflower usually considered undesirable in pastures due to its toxicity to livestock.

The common name “snakeroot” comes from an old and incorrect belief that this plant could help treat venomous snakebites.

Instead, if eaten, this plant is toxic to mammals and can kill cattle and horses (where the malady is called “trembles”) as well as humans, who can be killed by drinking milk from poisoned cattle. Because of its toxicity to livestock, this native plant is often considered a weed. Animals may ingest the toxic compounds by eating either fresh plants or hay and are most at risk when allowed to graze in wooded habitats where white snakeroot can benefit from disturbance by livestock and form dense stands.

Humans who have ingested the toxins by drinking the milk of cows that have eaten the plant display weakness, muscle spasms, vomiting, constipation, thirst, delirium, and coma. This plant is responsible for the deaths of many early settlers who drank milk from cows that had consumed the plant. It is estimated that in the early 1800s in parts of Ohio and Indiana, up to half of all fatalities were caused by “milk sickness.” One victim, apparently, was Abraham Lincoln’s mother.

Like thoroughworts, goldenrods, ironweeds, native asters, and many other composites that produce big clusters of flowers late in the season, snakeroot attracts a wide array of pollinators — butterflies, bees, wasps, flies, beetles, and more. The presence of these insects makes them a hunting ground for many kinds of spiders, assassin bugs, robber flies, and other predators. Insect-eating birds also keep watch on the flower clusters.

In addition to being a meeting place for insect diners, snakeroot and other wildflowers that offer big clusters of flowers are also a place for insect courtship and mating.

Several closely related plants are eaten by the caterpillars of some tiger moths and other moths, and apparently this species is among the food plants of these moths. The toxins are incorporated into the moths’ bodies as a predator deterrent.

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Similar Species
About Wildflowers, Grasses and Other Nonwoody Plants in Missouri
A very simple way of thinking about the green world is to divide the vascular plants into two groups: woody and nonwoody (or herbaceous). But this is an artificial division; many plant families include some species that are woody and some that are not. The diversity of nonwoody vascular plants is staggering! Think of all the ferns, grasses, sedges, lilies, peas, sunflowers, nightshades, milkweeds, mustards, mints, and mallows — weeds and wildflowers — and many more!