Description from Flora of China
Herbs, shrubs, or rarely treelike, with milky or, less often, clear latex. Leaves simple, opposite or occasionally whorled, very rarely alternate, usually without obvious stipules, margin nearly always entire. Inflorescences terminal, axillary, or extra-axillary, cymose, often condensed and umbel-like, occasionally a racemelike bostrychium. Flowers bisexual, 5-merous, actinomorphic. Sepals joined at base only, often with 5 or more basal glands in the sinuses. Corolla sympetalous, reflexed to urceolate or salverform; lobes valvate or overlapping in bud to right or left. Corona usually present, inserted on corolla, stamens, or both. Stamens 5, usually inserted at base of corolla tube and adhering to stigma head to form gynostegium; filaments usually connate to form a tube enclosing ovaries; anthers 4-celled (Periplocoideae and Secamonoideae) or 2-celled (Asclepiadoideae), often with a membranous apical appendage; pollen tetrads contained loosely on a spatulate translator with a basal corpusculum (Periplocoideae), or pollen united into waxy pollinia, each attached through a caudicle (stalk) to the retinaculum (gland) between adjacent anthers to form a pollinarium, pollinia 2 (Asclepiadoideae) or 4 (Secamonoideae) per pollinarium. Ovaries 2, free, superior; ovules numerous. Styles connate; stigma head fleshy. Fruit of 1 or 2 follicles. Seeds numerous, strongly compressed, with a coma (a prominent basal tuft of silky hairs). Chromosome number x = (8-)11 (or 12).
Some 250 genera and over 2000 species: widespread in tropical and subtropical regions, especially in Africa and southern South America, with a moderate representation in northern and southeastern Asia; 44 genera (four endemic) and 270 species (153 endemic) in China.
Some authorities include this family in the Apocynaceae. Genera 1-6 are sometimes placed in a separate family, the Periplocaceae, here regarded as a subfamily, Periplocoideae. Genera 7-10 belong to the Secamonoideae and the remaining genera to the Asclepiadoideae. Many Chinese taxa are known only from dried material, sometimes not well preserved, and it is likely that the study of living or spirit-preserved material could lead to a reassessment of the taxonomy of some of these endemic taxa.
All plant parts, especially the seeds and latex, are often poisonous. They contain various alkaloids and glycosides, many of which are used in medicine and as insecticides. A few succulent species (e.g., Stapelia gigantia N. E. Brown, Orbea pulchella (Masson) L. C. Leach, and O. variegata (Linnaeus) Haworth are grown by specialist collectors in China.
Tsiang Ying & Li Ping-tao. 1977. Asclepiadaceae. Fl. Reipubl. Popularis Sin. 63: 249-575.
(Authors: Li Ping-tao; Michael G. Gilbert, W. Douglas Stevens)