White Snakeroot (Ageratina altissima)


Sunflower Family (Asteraceae)

Other Names:

Eupatorium rugosum, Eupatorium ageratoides, E. urticaefolium, deerweed, deerwort, deerwort-boneset, fall poison, hemp-agrimony, Indian sanicle, milk-sickness plant, richweed, snakeroot, squaw-weed, stevia, white sanicle, white top.

Origin and Distribution:

White snakeroot is a native of North America. The plant is currently naturalized throughout southern Canada and all over the eastern half of the U.S. excluding areas in the extreme south. White snakeroot occurs everywhere in Ohio, but it is rarer in the northwest compared with other parts of the state. White snakeroot is a tall plant with rather showy clusters of small bright-white flowers so it is easy to spot in fields, meadows, thickets, woods, waste places, roadsides, lake edges, stream banks, and other shady areas in which it thrives. White snakeroot prefers moist forested areas and rich soils, but plants survive in dry places and may even persist in disturbed areas. The species grows best in basic soils.

Plant Description:

White snakeroot is a 3-foot-tall perennial herb. Distinctive features include opposite leaves, which are coarsely-toothed, rounded at the base, sharply-pointed at the tip, and attached to a long slender leaf stalk (petiole), and flat-topped clusters of small bright-white flowers. Ingesting leaves and stems of the plant produces a deadly condition known as "trembles" in animals, and humans can develop "milk sickness" by consuming milk from affected animals. White snakeroot reproduces by seeds and short rhizomes (horizontal underground stems).

  • Root System:

    The root system includes fibrous, branched roots and tough, knotty rhizomes (horizontal underground stems).

  • Seedlings and Shoots:

    Young leaves are thin, pale green, and have short hairs on the upper surface, edges, and veins. Leaf veins, consisting of the midrib and a simple vein on either side (3-nerved), are easy to discern on both the upper and lower surfaces. Stems and leaf stalks (petioles) of young plants are often purple-stained.

  • Stems:

    Stems are erect, leafy, 2 to 3 feet tall, and much branched near the top. Stems may be solitary or several may emerge in a cluster from the same root system.

  • Leaves:

    Leaves are opposite (2 leaves per node), thin, 2 1/2 to 7 inches long, broadly oval to lance-shaped, and 3-nerved. Larger leaves have a rounded base, sharp teeth around the edge, and taper to a point at the tip. Leaves attach to the stem by way of a slender petiole that is at least 1/4 as long as the leaf.

  • Flowers:

    Numerous flower heads are grouped into loosely-branched, flat-topped clusters arising from the axils of upper leaves. Each flower head is about 1/4 inch wide and contains 8 to 30 bright-white disk flowers.

  • Fruits and Seeds:

    The single-seeded fruits are brown or black, about 1/16 inch long, cigar-shaped, and tipped with a tuft of white hairs (pappus).

Similar Species:

White snakeroot can be separated from other Eupatorium species such as bonesets, Joe-Pye weeds, other snakeroots, and thoroughworts by its distinctive leaves that are opposite, sharply-toothed, 3-nerved, and attached to long petioles.


White snakeroot generally begins to flower in July and continues until September. The weed does not persist in cultivated areas. Plants should be pulled as soon as they appear or mowed close to the ground several times during the season before seeds form. Improving drainage may aid in control of this poisonous plant.


Leaves and stems of white snakeroot plants contain tremetol, which is extremely poisonous. The plant is unpalatable to animals, but they will consume it if other forage is scarce. If sufficient amounts of white snakeroot are consumed, animals develop a condition known as ''trembles'' that may cause death. Lactating animals excrete the toxin in their milk, which can then pass to humans drinking the milk. The condition produced, known as "milk sickness", was common in early colonial times. A great milk sickness epidemic occurred in local areas of the eastern U.S. in the early nineteenth century resulting in many deaths. Abraham Lincoln's mother, Nancy Hanks Lincoln, was among those who died. Eventually, the toxin in white snakeroot was identified as the cause. The condition is rare today because it is common to pool milk from different areas and herds for commercial production thereby diluting any tremetol present. Meat of animals that eat white snakeroot can also contain tremetol at levels toxic to humans consuming it. Dried plants in hay are toxic but not as poisonous as fresh plants.

Facts and Folklore:

  • Native Americans used the plant as a treatment for snakebites as well as for various diseases.

White snakeroot leaves.
Roots of white snakeroot.
White snakeroot stem and bloom.