This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Artemisia capillifolia Lam. Encycl. I: 267. 1783. Eupatorium foeniculeides Walt. Fl. Car. 199. 1788. E. foeniculaceum Wind. Sp. Pl. 3: 1750. 1804. E. capillifolium Small, Mem. Torr. Club 5: 311. 1894.
Erect, paniculately much branched, with the aspect of an Artemisia, the stem finely pubescent, 4°-10° high. Leaves crowded, glabrous or nearly so, alternate, pinnatifid into filiform segments, the lower petioled, the upper sessile; heads very numerous, about 1 1/2" high, short-pedicelled, racemose-paniculate, 3-6-flowered; bracts of the involucre in about 2 series, linear, cuspidate, narrowly scarious-margined, glabrous; flowers greenish-white.
In fields, Virginia to Florida. In ballast, at Philadelphia. Also in the West Indies. Sept.
E. maculatum L. Amoen. Acad. 4: 288. 1755. Eupatorium purpureum var. maculatum Darl. Fl.
Cest. 453. 1837. Eupatorium maculatum amoenum Britton, Mem.
Torr. Club 5: 312. 1894.
Similar to the two following specie:, scabrous or pubescent, often densely so, 2°-6° high. Stem usually striate, often rough and spotted with purple; leaver thick, ovate or ovate-lanceolate, coarsely dentate, verticillate in 3's-5's, or the upper ones opposite; inflorescence depressed, cymose-paniculate; pedicels and outer scales of the involucre pubescent; flowers pink or purple.
In moist soil, Newfoundland to New York, Kentucky, British Columbia, Kansas and New Mexico. Spotted boneset. Perhaps to be regarded as a race of E. purpureum. Aug.-Sept.
Eupatorium Bruneri A. Gray, Syn. Fl. 12: 96. 1884.
Eupatorium Rydbergi Britton, Manual 921. 1901.
Stem tall, pubescent, often densely so, at least above. Leaves verticillate in 3's-5's, rather slender-petioled, lanceolate, serrate, acuminate at the apex, narrowed at the base, scabrous above, finely densely pubescent and reticulate-veined beneath, 4'-6' long, £'-2' wide; inflorescence depressed or subpyramidal; outer bracts of the cylindric involucre pubescent; flowers pink or purple.
In moist soil, South Dakota to Wyoming, Nebraska and Colorado. Apparently erroneously recorded from Iowa. July-Sept.
Eupatorium purpureum L. Sp. Pl. 838. 1753. E. falcatum Michx. Fl. Bor. Am. 2: 99. 1803. Eupatorium purpureum var. angustifolium T. & G. Fl.
N. A. 2: 82. 1841. Eupatorium purpureum falcatum Britton, Mem. Torr.
Club 5: 312. 1894.
Glabrous or sparingly pubescent, simple or branched at the summit, 3°-10° high. Stem green or purple, terete or striate, usually smooth; leaves thin, verticillate in 3's-6's, ovate, oval, ovate-lanceolate or narrowly lanceolate, petioled, acuminate, serrate, 4'-12' long, 6"-3' wide, glabrous or slightly pubescent along the veins on the lower surface; inflorescence usually elongated; heads very numerous; involucre cylindric, its bracts pink, oblong, obtuse, imbricated in 4 or 5 series, the outer shorter; flowers pink or purple, occasionally white.
In moist soil, New Brunswick to Manitoba, Florida and Texas. Kidney-root. Skunk-weed. Indian gravel-root. Marsh-milk weed. Nigger-weed. Quill-wort. Motherwort. King- or queen-of-the-meadow. Aug.-Sept.
Eupatorium trifoliatum L. has the teeth of the leaves bluntly apiculate, but otherwise closely resembles E. purpureum and may not be specifically distinct.