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White Snakeroot Ageratina altissima (Eupatorium rugosum)


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White Snakeroot
credit: Sten Porse/CCSA

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Family: Asteraceae, Aster view all from this family

Description Solitary or clustered firm stems bear flat-topped clusters of small white fragrant flowerheads composed entirely of disk flowers.
Habit: native perennial herb; one or several stems, occasionally branched.
Height: 1-4 ft (30-120 cm)
Leaf: at base, opposite, long-stalked, heart-shaped, strongly serrated, 1.5-6 in (4-15 cm) long, 1-3.5 in (2.5-9 cm) wide; becoming smaller, lanceolate above.
Flower: small fuzzy button, white, rayless, .15-.5 in (4-12 mm) wide; held in round flat-topped terminal cluster, 3 in (75 mm) wide.
Fruit: tiny linear seed, tipped with white bristles.

Warning White Snakeroot is poisonous to livestock. The toxins will pass into milk produced by animals that ingest the plant, and the tainted milk can fatally poison humans.

Flower July to October.

Flower August - October

Habitat Lightly shaded: Woods and thickets, disturbed sites.

Range Eastern and central North America: New Brunswick and Maine, south to Florida, west to northeast Texas, north to North Dakota, east to Minnesota and southern Ontario.

Discussion Also known as richweed, snakeroot. Three varieties are recognized. Considered weedy or invasive in some areas. This plant used to be placed in the genus Eupatorium, as did Smaller White Snakeroot (A. aromatica), a nonaromatic plant despite its name; it has less coarsely toothed leaves, the upper ones stalkless. Other similar species are Late-flowering Thoroughwort (Eupatorium serotinum), which has long-stalked lanceolate leaves with 3-5 main veins, and Hyssop-leaf Thoroughwort (E. hyssopifolium), with very narrow leaves in whorls of 3-4.

Comments Spreads by seed and can become weedy.

Exposure Preference Shade to partial shade.

Native Distribution Eastern Canada to Saskatchewan, s. to West Virginia, upland Georgia & e. Texas

Site Preference Rich woods; thickets; clearings; shady river bottoms

Soil Preference Rich soils. pH 6-7.