Apocynaceae : The Oleander or Dogbane Family

Apocynaceae are very diverse in form. They can be tall rainforest trees to smaller trees, shrubs, lianas, vines, herbs, and sometimes succulent cactus-like plants. They have a white milky latex sap. Leaves are usually opposite, sometimes alternate or 3-whorled, entire with pinnate venation; stipules are generally lacking or reduced. Inflorescence is determinate (growth that terminates in flower in a cyme or panicle (irregularly compound flowers with pedicellate flowers) or with solitary flowers that are terminal to axillary (angle between leaf and stem). Flowers are actinomorphic (radially symmetrical with more than one plane of symmetry) or radial form with 5 sepals and 5 petals (free or fused) forming a tubular shaped corolla that are sometimes reflexed, often very showy, with scales or a coronal appendage on the inside of tube. There are usually 5 stamens, with short filaments attached to the corolla that frequently have appendages forming a hood or horn-shaped structure. Anthers are distinct or can adhere together forming a ring around the style. Pollen grains are slightly waxy, loosely sticking together, or they may be strongly adhered, often forming a hardened mass known as pollinia. The superior (sometimes half-inferior) ovaries are 2 carpels with styles and stigmas bound together into a connate structure. Each ovary contains 2 to many ovules with one thin-walled megasporangium (a tiny globe structure in which female spores are produced). A hypogenous disk is found at the base of each distinct ovary. At the apex of the bound carpels is an enlarged structure or stylar head, differentiated into 3 zones specialized for pollen reception, that secretes a sticky fluid from its middle portion. Nectar can also be secreted from the staminal tube or a coronal appendage, nectar glands, or a disk. Each ovary can develop into paired fleshy berries, drupes, or dry follicles. Seeds are flat, often with apical tufts of hair at one end and have a straight-to-bent embryo. Seeds with hair are generally wind dispersed, while fleshy and bright colored fruits are often consumed and dispersed by birds or small mammals. Examples of latter type are found mostly in tropical genera such as Kopsia, Rauvolfia, Carissa, and Ochrosia. The formation of the stylar head and specialized anthers in Apocynaceae flowers is highly specialized and exhibits the near fusion of the androecium (stamens collectively) and gynoecium (the pistil or pistils as a group). Pollinators of Apocynaceae are diverse and include butterflies, moths, bees, and even flies. While visiting flowers the mouths of these insects become sticky with the fluid excreted from the stylar head, facilitating the collection and spread of pollen to other flowers. In the pollination of some genera the insect's legs may get lodged between anthers. When the insect pulls free it often takes with it the pollinia, which will then be transported to the stylar head of the next visited flower. Apocynaceae have an internal phloem (tissue that conducts organic food material) as well as tissues with laticifers containing a milky sap that contains glycosides, alkaloids and iridoids.

Apocynaceae comprise some 200 genera and 2,000 species, most commonly found in subtropical and tropical regions, though with some genera habiting temperate areas. Major genera include (with number of species in parentheses) Asclepias (230), Tabernaemontana (230), Cynanchum (200), Ceropegia (150), Hoya (150), Matelea (130), Rauvolfia (110), Gonolobus (100), Secamone (100), and Mandevilla (100). Most members of the Apocynaceae family are toxic or have medicinal properties. Well-known United States genera include Angadenia, Apocynum, and Sarcostemma. The genus Catharanthas includes the Madagascar periwinkle, which produces vincristine and vinblastine used in antileukemia drugs. The genus Rauvolfia produces reserpine, used to treat hypertension, while the genus Strophanthus provides strophanthin, a cardiac glycoside used in heart ailments. In Africa, Strophanthus spp. has long been used for tipping poison arrows and, more recently, for medicinal purposes. Some species such as the Carissa carandas or C. macrocarpa (Natal plum) are harvested for their edible fruits. Historically, the genus Carpodinus (as well as Landolphia, Hancornia, Funtumia, and Mascarenhasia) provided an inferior source of rubber. Hancornia speciosa (Mangabiera) is a South America species grown for its fruit but whose sap is also harvested for rubber. Members of the Apocynaceae family commonly have a fragrant scent in addition to showy flowers that favor their selection as ornamentals. In Hawaii the fragrant bark and leaves of Alyxia oliviformis and Plumeria obtusa are used to make popular leis. Wood from Tabernaemontana divaricata is used for perfume and incense in addition to its medicinal properties. Other important ornamentals include species of the genera Nerium (oleander, which is extremely poisonous), Stapelia (carrion flower), Trachelospermum (confederate jasmine) Thevetia (luckynut), and Vinca (periwinkle). In the United States, genera that provide ornamentals include Amsonia (bluestar) and Catharanthus.

To date 6 species of this family (with one species having several variants) have been collected in the Oapan, San Juan Tetelcingo, and Ameyaltepec area. They belong to the genera Plumeria (1 species, several variants), Rauvolfia (1 species), Stemmadenia (1 species), Thevetia (2 species), and Vallesia (1 species).

The following members of this family have been documented in sources consulted on Guerrero flora: Haplophyton cinereum, Nerium oleander, Plumeria acutifolia, Plumeria rubra, Rauvolfia heterophylla, Rauvolfia longifolia, Rauvolfia tetraphylla, Stemmadenia mollis, Stemmadenia obovata, Tabernaemontana sp., Thevetia ovata, Thevetia thevetioides, Tonduzia parvifolia, Urechites karwinskii, and Vallesia glabra.

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