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 rubra L. Sp. Pl. 217. 1753.
Nearly glabrous throughout; stem usually simple, 1°- 4° high. Leaves opposite, rather distant, short-petioled, ovate, lanceolate or the lower sometimes oblong, rounded or subcordate at the base, gradually acuminate, rather firm, 3'- 8' long, l'- 21/2' wide, the primary nerves wide-spreading; umbels 1-4, many-flowered; peduncles shorter than or equalling the upper leaves; pedicels slender, downy, 1/2'- 1' long; corolla-segments and hoods lanceolate-oblong, purplish red, or the hoods orange-red, 3"-4" long, or flowers sometimes greenish; horns of the hoods very slender, nearly straight; fruiting pedicels deflexed, the follicles erect, spindle-shaped, glabrous, about 4' long.
In moist soil, New Jersey and Pennsylvania to Florida, Missouri, Louisiana and Texas. June-July.
Asclepias purpurascens L. Sp. Pl. 214. 1753. ?Asclepias amoena L. Sp. Pl. 214. 1753.
Stem stout, puberulent or glabrous, usually simple, 2°-4° high, leafy to the top. Leaves ovate, elliptic or oblong, short-petioled, acute or obtuse and mucronulate at the apex, narrowed or rounded at the base, nearly glabrous above, finely tomentose beneath, 3'-8' long, 1 1/2'-3' wide, the primary nerves very wide-spreading; umbels many-flowered, borne in several of the upper axils, or sometimes solitary; peduncles stout; pedicels slender, puberulent, 1'- 1 1/2' long; corolla deep purple, its segments oblong to oblong-lanceolate, about 3" long; column very short and thick; hoods oblong or ovate, nearly twice as long as the anthers, pale red or purple, the horns broad at the insertion, short-subulate and incurved at the apex; fruiting pedicels deflexed, the downy follicles nearly erect, 4'-5' long.
In dry fields and thickets, New Hampshire to North Carolina, west to southern Ontario, Minnesota and Arkansas. Ascends to 2000 ft. in the Cats-kills. June-Aug.
Asclepias incarnata L. Sp. Pl. 215. 1753.
Stem slender, glabrous, or puberulent in 2 lines above, branched or rarely simple, 2°-4° high, leafy to the top. Leaves lanceolate or oblong-lanceolate, acuminate at the apex, narrowed, obtuse or sometimes subcordate at the base, 3'- 6' long, 1/2'- 1 1/2' wide, the primary nerves not wide-spreading; petioles 3"- 6" long; umbels usually numerous, corymbed, many-flowered; pedicels pubescent, 5"- 10" long; corolla red or rose-purple, rarely white, its lobes oblong, about 2" long; column more than one-half as long as the obtuse pink or purplish hoods; horns slender, incurved, longer than the hoods; anther-wings entire, or obscurely notched at the base; fruiting pedicels erect or incurved; follicles erect, 2-3 1/2' long, sparingly puberulent.