Tall Thoroughwort (Eupatorium Altissimum)

Features and Characteristics

Eupatorium altissimum, commonly called tall boneset or tall thoroughwort, is a somewhat weedy perennial herb that grows from branching rhizomes to 2-6’ tall on single upright stems that branch toward the top. It is native to dry upland prairies, open woods, thickets, clearings and fields throughout eastern and central North America from New York to Ontario to Minnesota and Nebraska south to Texas and Florida.

Simple, opposite, elliptic-lanceolate, leaves (2-6” long) are serrate above the middle, tapered toward the tip and base, and pubescent underneath. Three parallel veins run the length of each leaf. Star-shaped, dull white to cream disk flowers (ray flowers absent), each with 5 triangular petal-like lobes, bloom from August to October in flattened clusters (corymbs to 4-8” across) rising from the stem tops and upper leaf axils. Fruits are resinous-glandular achenes.

Plants in this species are apomictic polyploids (3 or more sets of chromosomes per cell) except for some diploid (2 sets of chromosomes per cell) populations which are only found in the Ozark Region (Missouri-Arkansas).

Genus name comes from the Greek name for these herbaceous and shrubby plants in honor of Mithridates VI Eupator, 132-63 B.C., King of Pontus, who reportedly discovered the medicinal uses for some Eupatorium species plants.

Specific epithet means especially tall or towering in reference to the height of the plant.