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..
Asclepias syriaca L. Sp. Pl. 214. 1753.
Stem stout, usually simple, 3°-5° high, finely pubescent at least above. Leaves oblong, oval or ovate, finely and densely pubescent beneath, soon glabrous above, acute or obtuse and cuspidate at the apex, obtuse, narrowed or subcordate at the base, 4'- 9' long, 2-41/2' wide, the primary nerves wide-spreading; petioles stout, 3"-8" long; umbels several or numerous; peduncles pubescent or tomen-tose, 1 1/2'-3 1/2' long; pedicels 1'-2' long; corolla green-purple or greenish-white, its segments oblong-lanceolate, 3 "-4" long; column short and thick, the hoods ovate-lanceolate with a tooth on each side, longer than the anthers and the incurved horn; follicles 3'- 5' long, erect on recurved pedicels, tomen-tose and covered with short soft processes.
Asclepias kansana Vail, of Kansas, differs by erect-spreading hoods of the corolla and more densely tomentose follicles.
Asclepias speciosa Torr. Ann. Lyc. N. Y. 2: 218. 1826. A. Douglasii Hook. Fl. Bor. Am. 2: 53. pl. 152. 1834.
White-tomentose or canescent all over, or gla-brate below, pale; stem simple, stout, 1°-2 1/2° high. Leaves thick, broadly ovate or oval, obtuse and cuspidate or acute at the apex, subcordate, rounded or narrowed at the base, petioled, 3'- 8' long, 2'-4' wide; peduncles 1'- 3' long; umbels several or rarely solitary, many-flowered; pedicels stout, 9"-18" long; corolla purple-green, its segments oblong or ovate-oblong, 4"-6" long, tomentose on the outer face; column very short or none; hoods lanceolate, 5"-7" long, obtusish, expanded and with 2 blunt teeth below, the apex ligulate, 5-7 times as long as the anthers; horn short, inflexed; follicles erect or spreading on the recurved fruiting pedicels, 3'- 4' long, densely woolly and covered with soft spinose processes.
In moist soil, Minnesota to British Columbia, south to Kansas. Utah and California. May-July.
A. arenaria Torr. Bot. Mex. Bound. Surv. 162. 1859.
Densely tomentose-canescent all over, stems simple, ascending or erect, stout, 1°-2° high. Leaves obovate or oval, wavy-margined, thick, obtuse or retuse and cuspidate at the apex, truncate, subcordate, obtuse, or rarely some of them narrowed at the base, 2' - 4' long, 1 1/2' - 3' wide, the angle of the primary nervation broad; umbels densely many-flowered, short-peduncled or sessile; corolla greenish-white, its segments oval-oblong, 4"- 5" long; column 1"- 2" high; hoods oblong, truncate at each end, oblique at the apex, longer than the anthers, with a broad tooth on each side within; horn semi-lunate with an abruptly incurved subulate apex; follicles puberu-lent, 4'-5' long, erect on the decurved fruiting pedicels.
On sand-bars and hills along rivers, Nebraska and Colorado to Mexico and New Mexico. June-Sept.