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..
Finely tomentose all over; stem simple, usually slender, erect, 10'- 2° high. Leaves oval, ovate, oblong or ovate-lanceolate, acute or obtuse and mucronulate at the apex, rounded or narrowed at the base, 2'-3' long, 1/2' - 1 1/2' wide, short-petioled, the upper surfaces becoming glabrate at maturity; umbels solitary or few, several-many-flowered; peduncles short; corolla greenish-white or purplish, its segments ovate-oblong, obtuse, a'-3" long; column very short; hoods oval-oblong, yellowish, nearly twice as long as the anthers, bearing a large acute tooth on each of the inner margins; horn subulate, incurved over the stigma; follicles ascending on the reflexed fruiting pedicels, pubescent.
Asclepias brachystephana Engelm.; Torr. Bot. Mex. Bound. Surv. 163. 1859.
Puberulent when young, soon glabrate; stems clustered, often branched, spreading or ascending, 6'- 12' long. Leaves mostly opposite, lanceolate or linear-lanceolate, thick, long-acuminate at the apex, rounded, subcordate or narrowed at the base, 2-5' long, 2"-6" wide, or the lowest shorter; petioles 1"-4" long; umbels several, terminal and axillary, few-flowered; peduncles short; pedicels densely woolly, equalling or longer than the peduncles; corolla greenish-purple, its segments about 2" long; column very short or none; hoods ovate, obtuse, shorter than the anthers, the short erect-incurved horn slightly exserted; follicles erect on the spreading or decurved fruiting pedicels, downy or hoary, acuminate, 2'-3 1/2' long.
In dry soil, Kansas (according to B. B. Smyth), Wyoming to Texas, Arizona and Mexico. June-Aug.
Asclepias perennis Walt. Fl. Car. 107. 1788.
Puberulent above, glabrous below; stem slender, simple or branched, erect, 1 °-3° high. Leaves thin, opposite, lanceolate, oblong or ovate-lanceolate, slender-petioled, acuminate or acute at both ends, 2'- 6' long, 1/4' - 1' wide, nearly glabrous; umbels solitary or several and corymbose; peduncles 1' - 2' long; pedicels slender, 1/2' - 1' long; flowers small, white; corolla-segments oblong, 1"-2" long; column about 1/2" high; hoods oval, erect, entire, about as long as the anthers, shorter than the subulate-filiform incurved horn; follicles glabrous, erect on the nearly erect fruiting pedicels; seeds 5"-6" long, 3 1/2"- 4 1/2" wide, thin, usually without coma.
On river-shores and in wet places, North Carolina to Indiana, Illinois and Missouri, south to Florida and Texas. May-Aug.