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..
Helian hus parvifloms Bernh.; Spreng. Syst. 3: 617.
1826. Not H.B.K. 1820. H. microcephalus T. & G. Fl. N. A. 2: 329. 1842.
Stems slender, glabrous, branched above, or rarely simple, 3°- 6° high. Leaves thin or thin-nish, petioled, most of them opposite, lanceolate, or the lower ovate-lanceolate, rough above, canes-cent or puberulent beneath, long-acuminate at the apex, narrowed at the base, serrulate, or the lower serrate, 3' - 7' long, 1/2' - 1 1/2' wide; heads commonly several or numerous, 1' - 1 1/4' wide, borne on slender, sometimes roughish peduncles; involucre campanulate, 4"- 5" broad, its bracts lanceolate or ovate, acute or acuminate, ciliolate, the tips of the outer ones spreading; chaff of the receptacle oblong, entire, or 3-toothed; rays 5-10; disk yellow; achenes nearly glabrous; pappus usually of 2 subulate awns.
Helianthus giganteus L. Sp. Pl. 905. 1753.
Perennial by fleshy roots and creeping rootstocks; stems hispid or scabrous, at least above, branched near the summit, or simple, 3°- 12° high. Leaves sessile or short-petioled, firm, lanceolate, very rough above, rough-pubescent beneath, serrate or denticulate, acuminate at the apex, narrowed at the base, many or all of the upper ones alternate but sometimes all opposite, 2'- 6' long, 2' - 6' wide; heads usually several, mostly long-peduncled, 1 1/2' - 2 1/2' broad; involucre hemispheric, its bracts squarrose, lanceolate-subulate, hirsute or ciliate, commonly as long as the diameter of the yellowish disk; chaff of the receptacle oblong-linear, acute; achenes oblong, glabrous; rays 10-20; pappus of 2 subulate awns.
In swamps and wet meadows, Maine and Ontario to Saskatchewan, Florida, Louisiana and Colorado. Stem commonly purple. Aug.-Oct.
Helianthus ambiguus (A. Gray) Britton, differing in having all but the uppermost leaves opposite and rounded at the base, found on Long Island, New York, and recorded from Georgia, appears to be a hybrid, with this species one of its, parents.
Perennial by fleshy roots and thickened rootstocks; stems stout, scabrous or hispid below, 2°- 12° high. Leaves sessile or short-petioled, long-lanceolate, folding in drying, alternate or the lower opposite, very rough on both sides, rigid, acuminate or acute at both ends, denticulate or entire, 3' - 7' long, 1/2' - 1 1/2' wide; heads few or numerous, 2-3' broad on stout densely rough-pubescent peduncles; involucre hemispheric, its bracts lanceolate, acuminate, squarrose, densely strigose-pubescent, often 9" long; disk yellowish; rays 15-30; chaff linear, acute, pubescent above; achenes linear-oblong, glabrous or nearly so; pappus commonly of 2 lanceolate awns.
On dry prairies, Minnesota and Manitoba to Saskatchewan, Missouri, Nebraska and Texas. Locally adventive eastward. Aug.-Oct.