APOCYNACEAE (Dogbane Family)

Contributed by David J. Bogler

Plants herbs (shrubs or trees elsewhere), often with rhizomes or a woody rootstock, or sometimes lianas. Stems sometimes twining, usually with milky sap. Leaves opposite or alternate, rarely appearing whorled, simple, or entire. Stipules absent or inconspicuous. Inflorescences axillary or terminal clusters or panicles, or the flowers solitary. Flowers perfect, hypogynous, actinomorphic. Calyces deeply 5-lobed. Corollas 5-lobed, commonly funnel-shaped to trumpet-shaped, the interior of the tube sometimes with hairs, scalelike appendages, or outgrowths, the lobes overlapping and contorted (twisted) in bud. Stamens 5, alternating with the corolla lobes, the filaments short, fused to the corolla tube, lacking appendages, the anthers forming a close ring around the stigma, free from the stigma but often more or less held in place by sticky secretions. Pistil of 2 carpels, these free below but fused above the ovary. Each ovary superior, 1-locular, with numerous ovules, the placentation parietal. Style 1 per flower, the stigma capitate or somewhat conical, sometimes slightly 2-lobed, often relatively large, sometimes with a small, cuplike wing or other outgrowths. Fruits follicles (berries or capsules elsewhere), potentially 2 per flower. Seeds usually numerous, glabrous or with a tuft of silky hairs at the end opposite the attachment point. About 300 genera, about 2,000 species, nearly worldwide, but most diverse in tropical regions.

The milkweed family, Asclepiadaceae, is included in the Apocynaceae in some of the recent botanical literature, but the two groups are treated in the traditional sense as separate families here. See the treatment of Asclepiadaceae for further discussion.

A number of species of Apocynaceae are popular ornamentals in gardens and greenhouses, including members of some native genera, as well as the exotic genera Allamanda L. (allamanda), Carissa L. (natal plum), Catharanthus G. Don (Madagascar periwinkle, rosy periwinkle), Nerium L. (oleander), Pachypodium Lindl. (pachypodium, Madagascar palm), Plumeria L. (frangipani), Thevetia L. (yellow oleander), and Vinca L. (periwinkle). In the tropics, a number of genera include timber trees and fiber plants. Members of the Apocynaceae contain a diverse assortment of alkaloids and other compounds. Most of the species are considered poisonous. Because of this complex biochemistry, some species have been used medicinally for a variety of ailments. Some of these medicinal uses have been investigated and have resulted in the development of important pharmaceuticals. For example, Catharanthus roseus (L.) G. Don is the source of alkaloids important in the treatment of leukemia and certain cancers; reserpine, which is used to treat schizophrenia and hypertension, comes from Rauvolfia L.; and Strophanthus DC. is the source of strophanthin, which is used in treating heart disease and as a precursor in the manufacture of cortisone. A number of genera also have been investigated as possible sources of latex for producing rubber.