Now classified as Ageratina altissima by most botanists, the genus Eupatorium having been broken up into a number of smaller concerns by the FTC.
One of our most decorative late-summer and autumn flowers, White Snakeroot lights up the edge of the woods and can form a perfect ornamental border around a field. Its beauty comes at a price: it’s poisonous to cattle, and the poison can be transmitted through their milk. “Milk sickness” killed Abraham Lincoln’s mother. But if you don’t have cattle, there’s no reason not to enjoy this beautiful wild native. These plants grew at the edge of the woods in Mount Lebanon, where they were blooming in the middle of September.
As a member of the Composite family, this species is especially interesting for the way the individual little five-parted flowers are easily distinguishable in the heads. It’s a good plant for demonstrating the construction of a Composite flower to children.
Flowers: Heads discoid (that is, with no ray flowers), in irregular flattish corymbs; flowers pure white, with protruding stamens, also white.
Leaves. Opposite; oval, pointed, toothed, finely rough; underside with many prominent ribs; lower leaves flattish at base or almost cordate; on petioles about 1/3 the length of the leaves.
Stem: Smooth, flexible; much branched from leaf axils; averaging about 4 feet, but quite variable and can be much taller.
Gray lists this plant as Eupatorium urticaefolium:
EUPATÒRIUM [Tourn.] L. THOROUGHWORT. Heads discoid, 3-many-flowered; flowers perfect. Involucre cylindrical or bell-shaped, of more than 4 bracts. Receptacle flat or conical, naked. Corolla 6-toothed. Achenes 6-angled ; pappus a single row of slender capillary barely roughish bristles. — Erect perennial herbs, often sprinkled with hitter resinous dots, with generally corymbose heads of white, bluish, or purple blossoms, appearing near the close of summer. (Dedicated to Eupator Mithridates, who is said to have used a species of the genus in medicine.)
1. EUPATORIÜM proper. Receptacle flat.
Heads 5-30-flowered; involucral brada nearly equal, in one row or but a very few of the outermost shorter; leaves opposite, ovate, petioled, triple-nerved, not resinous-dotted.
Leaves broadly ovate; flowers pure white.
E. urticaefòlium Reichard. (WHITE SNAKEROOT.) Smooth, branching, 0.5-1 m high; leaves broadly ovate, pointed, coarsely and sharply toothed, long-petioled, thin, 7-12 cm. long; corymbs compound. (E. ageratoides L. f.) — Rich woods, not rare. Var. villicaúle Fernald. Stems and petioles viscidvillous. — Pa. (Heller) to Va. (Curtías).