Stems stout, rigid, hairy, branched above, 2 to 5 feet high from a perennial root. Leaves tough, veiny and wrinkled on both surfaces, opposite and united by their bases (connate-perfoliate), the upper pairs usually not united, lanceolate, long pointed at the apex, 4 to 8 inches long, 1 to 11/2 inches wide, pubescent on the under surface, the margins finely crenate-toothed. Inflorescence consisting of many heads in a rather congested, nearly flat-topped cyme; each head one-sixth to one-fourth of an inch high and ten to sixteen-flowered, dull leaden-white in color. Involucre campanulate, pubescent, with lanceolate bracts arranged in two or three series.
Common in wet meadows and low grounds, especially along streams in marshes and swamps, Nova Scotia and New Brunswick to Manitoba, south to Florida, Texas and Nebraska. Flowering in late summer, from July to September. In former times and even yet in some rural sections, boneset tea, made from the dried leaves of this plant, is prized for certain medicinal properties.
Memoir 15 N. Y. State Museum
Common Thoroughwort; Boneset - Eupatorium perfoliatum