Ageratina altissima

Did You Know?

• A cultivar sold as Eupatorium rugosum 'Chocolate' is grown for its dark-tinted foliage, which becomes chocolate black in sunny locations.
• The genus name Ageratina comes from Greek meaning 'un-aging', referring to the flowers keeping their color for a long time.
• The species is native in Canada in Quebec, Ontario, and the Northwest Territories.

Description

Plants grow upright or ascending to 1.5 m tall, forming single or multi-stemmed clumps in mid to late summer and fall. Stems are smooth with opposite leaves spaced well apart, each leaf pair at a 90-degree angle from the pair above and below. The upper part branches in opposite pairs. Leaves have sharply serrated margins and reach 6 in long. Flat-topped panicles or compound corymbs of white flower heads appear at branch ends, measuring 2–6 in across. After blooming, small seeds with fluffy white tails disperse by wind. The plant also spreads by rhizomes. Two varieties exist: Ageratina altissima var. altissima and var. roanensis, differing in phyllary length and apex shape.

Ecology

The plant blooms from July to October, attracting butterflies, moths, bees, wasps, and flies. It serves as a larval host for moths including the Clymene moth (Haploa clymene), Leucospilapteryx venustella, and the hitched dart moth (Melanchra adjuncta). Insect-induced galls on stems are caused by Asphondylia eupatorii, Neolasioptera eupatorii, and Schizomyia eupatoriflorae.

Toxicity

White snakeroot contains the toxin tremetol. When cattle consume the plants, their meat and milk become contaminated, and humans ingesting these products can develop tremetol poisoning, also called milk sickness. Although 80% of the toxin tremetone decreases after drying and storage for five years, the plant's toxic properties remain. During the early 19th century, many European American settlers unfamiliar with snakeroot died from milk sickness in the Midwest and Upper South.

Nancy Hanks Lincoln, mother of Abraham Lincoln, possibly died from it in 1818. Dr. Anna Pierce Hobbs Bixby is credited with identifying the plant as the cause in the 1830s; legend says a Shawnee woman taught her about its properties. The plant is also poisonous to horses, goats, and sheep, causing depression, lethargy, hind foot placement changes, nasal discharge, excessive salivation, arched posture, and rapid or difficult breathing.