PLANT: Perennial herbs, rarely shrubs or subshrubs. STEMS: pubescent to glabrous, non-glandular. LEAVES: opposite, whorled or irregularly alternate. INFLORESCENCE: umbelliform cymes, the flowers opening synchronously. FLOWERS: showy; calyx divided nearly to the base; corolla deeply divided, the lobes mostly reflexed, displaying the prominent crown and anther head, in ours glabrous to sparsely hairy outside, mostly minutely pustular-hairy inside; crown extremely variable in form, arising from the column below each anther, of 5 distinct, infolded to subglobular segments (hoods), each with an inner crest or appendage (horn), rarely the horn entirely absent; anther head elevated on a more or less conspicuous column, the anther wings mostly flaring outward toward the base giving the anther head a truncate-conic form; pollinia pendulous from the translator arms, flat, asymmetrically obovate to oblanceolate; stigma head truncate with a central depression. FOLLICLES: mostly erect on deflexed pedicels, the surface smooth, rarely tuberculate. NOTES: Ca. 150 spp.; in the Americas, particularly Mex. and the U.S., also Afr. (For Aesculapius, legendary Greek physician and god of medicine.) A genus of many documented uses among American Indians; also stem fibers have been used for cordage and textiles, the silky seed hairs as a kapok substitute, and the latex for rubber; the latex has most recently been investigated as a petroleum substitute. Milkweed cardenolides, physiologically active compounds related to digitalis, are of interest for their powerful emetic and cardiotonic properties. A number of species are toxic to livestock but are distasteful and are seldom eaten. Woodson, R. E., Jr. 1954. Ann. Missouri Bot. Gard. 41:1-211. REFERENCES: Sundell, Eric. 1994. Asclepiadaceae. J. Ariz. – Nev. Acad. Sci. Volume 27, 169-187.