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..
Eupatorium pilosum Walt. Fl. Car. 199. 1788. ? Eupatorium verbenaefolium Michx. Fl. Bor.
Rough-pubescent, slender, 3°-8° high, branched at the summit. Leaves opposite, or occasionally in 3's, ovate-oblong, usually obtuse or blunt-pointed, closely sessile or rarely short-petioled, rounded or narrowed at the base, crenate-dentate, or incised, 2'-4' long, 1/2'-1' wide, the upper pairs distant and small; inflorescence cymose-paniculate; heads 5-flowered, about 3 ' high; involucre campanulate, its bracts linear-lanceolate, acute, imbricated in about 3 series, densely pubescent, the outer shorter; flowers white.
In moist soil, Massachusetts to Pennsylvania, West Virginia, Florida and Louisiana, mostly near the coast. Called also wild hoar-hound. July-Sept.
E. rotundifolium L. Sp. Pl. 837. 1753.
Pubescent, branched at the summit, 1°-3° high. Leaves opposite, sessile, broadly ovate, often as wide as long, acutish or obtuse, truncate to subcordate at the base, coarsely dentate-crenate, 1'-2' long, ascending; inflorescence cymose-paniculate; heads about 5-flowered, 2"-3" high; involucre campanulate, its bracts linear-oblong, acutish, densely pubescent, imbricated in about 3 series, the outer shorter; flowers white.
In dry soil, Rhode Island to Pennsylvania, Florida, Kentucky, Arkansas and Texas. Erroneously reported from Canada. July-Sept.
E. pubescens Muhl.; Willd. Sp. Pl. 3: 1755. 1804.
Puberulent or pubescent, branched above, usually taller than the preceding species. Leaves opposite, ovate, sessile, often twice as long as wide, acute at the apex, rounded or subtruncate at the base, coarsely dentate with acute or acutish teeth, or the lower incised; inflorescence cymose-paniculate, sometimes 10' broad; heads 5-8-flowered, 2"-3" high; involucre campanulate, its linear-oblong bracts in 2 or 3 series, the outer shorter; flowers white.
In dry soil, Maine to Pennsylvania, South Carolina, West Virginia and Tennessee. Recorded from Florida. Ascends to 3000 ft. in Virginia. July-Sept.
E. perfoliatum L. Sp. Pl. 838. 1753. Eupatorium truncatum Muhl.; Willd. Sp.
Pl. 3: 1751. 1804. Eupatorium perfoliatum truncatum A. Gray, Syn. Fl. 1: Part 2, 99. 1804.
Pubescent, stout, branched above, 2°-5° high. Leaves opposite, or rarely in 3's, connate-perfoliate, or the upper, rarely all, truncate and separated at the base, divaricate, lanceolate, long-acuminate with a slender apex, finely crenate-ser-rate, rugose and pubescent beneath, 4's' long, 1'-1 1/2' wide; heads crowded, 10-16-flowered, 2"-3" high; involucre cam-panulate, its bracts lanceolate, acutish, in 2 or 3 series, pubescent, the outer shorter; flowers white, rarely blue.