ASCLEPIADACEAE, the milkweed family, a distinctly marked group of dicotyledonous plants comprised chiefly of shrubs and woody vines, though many are perennial herbs, mostly with a milky juice. Like the Apocynaceae (q.v.), to which they are closely related, most of the species, about 1,700 in number and divided into some 32o genera, are tropical. The continent of Africa is the headquarters of the family. The flowers are regular, sympetalous and usually arranged in umbels, though sometimes in cymes or racemes; the fruit from each flower consists of a pair of more or less fleshy pods containing numerous seeds which are usually appendaged with a long tuft of hairs. As regards forms and habits of growth, the Asclepiadaceae ranks among the most unusual of plant families. Many are rope-like lianas of equatorial forests. Others are epiphytes with greatly modified leaves, which, in some species, take the form of pitchers for holding water. Cer tain South African species are fleshy, cactus-like plants. Still others form a cluster of leafless, whip-like stems. In some species the stems develop tuberous bases in which water is stored.
Although the family contains no economic plants of the first rank, numerous species are useful. Many are of value medicinally; the milky juice of the so-called cow-plant (Gymnena lactiferum), of Ceylon, is edible as is that of its South African counterpart (Oxystelma esculentum), and the tender shoots of various species are eaten as salads and pot herbs. Others are dye-plants, as, for example, Marsdenia tinctorium; various species produce caout chouc, and others yield bast fibres. The juice of Gonolobus is used for poisoning arrows, and that of Cynanchum for poisoning fish. A large number are cultivated as ornamental plants, among which are the mosquito plant (Cynanchum), the silk-vine (Periploca graeca), the carrion-flower (Stapelia variegata), and the fragrant wax-plant (Hoya carnosa) and stephanotis (S. floribunda). The madar or oschur (Calotropis procera), native to southwestern Asia, is believed to be the sodom apple of the Bible ; the bark of the Indian madar (C. gigantea) yields a fibre and the seeds a floss.
Of some 8o representatives of the family native to the United States and Canada, the most common and conspicuous are the milkweeds (Asclepias). Among the best known of these are the butterfly-weed (q.v.) and the swamp milkweed (A. incarnata), both with showy, handsome flowers. The blood-flower (A. curassa vica), native to tropical America, and frequently grown in green houses, has become naturalized in the southern United States.
(See MILKWEED.)