The Apocynaceae are trees, shrubs, herbs, and vines or lianas, sometimes succulent, usually with milky sap.  The family includes about 355 genera and 3,700 species. The leaves are simple, usually opposite and decussate, sometimes whorled or alternate; stipules are reduced or absent. The flowers are bisexual and actinomorphic or sometimes weakly zygomorphic. The calyx consists of usually 5 free or basally connate lobes. The corolla is sympetalous and usually 5-lobed, often with adnate coronal appendages. The stamens are as many as corolla lobes and alternate with them, adnate to the corolla tube (perigynous zone). The anthers are introrse and usually adherent to the surface of the (often enlarged) stigma, or the anthers may be joined more firmly to the stigma so as to form a gynostemium (gynostegium) which commonly is also conjoined to coronal appendages.  Pollen is released as monads, tetrads, or in agglutinated masses called pollinia.  The pollinia are usually in pairs that are transferred as a unit during pollination.  The gynoecium consists of a single compound pistil of 2 carpels that may be distinct at the level of the superior or rarely partly inferior ovary but which are united by the single style and stigma, or at least by the single stigma.. When distinct, each ovary typically has a single locule with few to numerous ovules on marginal placentae; when connate, the placentation is axile (2 locules) or intruded parietal (1 locule). A nectary consisting of 5 glands or an annular ring is usually found at the base of the ovary. The fruit is commonly a follicle, capsule, or berry. The seeds usually are flat and winged or have a tuft of hairs at one end.

Each "thumbnail" image below is linked to a larger photograph.

Alyxia oliviformis, maile. The bark and leaves of this native Hawaiian vine are used to make a fragrant lei.
Allamanda cathartica, allamanda, lani-ali'i. Climbing ornamental shrub from Brazil, with large yellow tubular flowers to about 3 inches in diameter. The leaves contain a cathartic.
Allamanda schottii, allamanda. Small shrub from Brazil, with yellow tubular flowers smaller than preceding species. Fruits globose, prickly, burlike. 
Alstonia scholaris, devil tree.  Native from India to Solomon Islands. UH Campus, Honolulu, HI, February, 2005.
Beaumontia jerdoniana. This species has a very broad corolla tube which makes it possible to easily see the anthers adhering to the stigma.
Carissa macrocarpa, Natal plum. In this species the tube of the 5-lobed corolla is very narrow. In the first image note the paired red fruits that have developed from the separate ovaries of the single pistil. They diverged during the maturation period following abscission of the unifying style (one ovary often aborts).
Cascabela thevetia, be-still tree. This is another example of a poisonous member of the family. Note the small droplets of white sap seeping out of the lower half of the fruit.
Catharanthus roseus, Madagascar periwinkle. Perennial herb or low shrub from W. Indies, with white or pink, slenderly tubular flowers; often used as a ground cover.
Cerbera manghas. Note the white sap oozing from the cuts on the fruit. Sap from species such as this have been used in arrow poisons.
Nerium oleander, oleander. This is a highly poisonous member of the family. The flowers have a fringe of extra appendages in the throat of the corolla.
Pachypodium lamerei, Madagascar palm, UC Davis greenhouse.
Plumeria obtusa, Singapore plumeria. This is one of the very common lei flowers in Hawaii.
Stemmadenia littoralis, lecheso. Small ornamental tree from Central America with paired oval leaves about 6 inches long and yellow-centered white tubular flowers about 2 inches or more in length. Note the complete separation of the two carpels in the developing fruit on the right (one carpel dehiscing as a follicle).
Strophanthus sp.
Tabernaemontana divaricata, Apocynaceae, paper gardenia, crape jasmine. Shrub from S.E. Asia, with white, often "doubled" flowers. Wood used for perfume and incense; plant has medicinal value but roots said to be poisonous.
Thevetia ahouai (identification courtesy of George de Verteuil)
Vinca major, periwinkle.  OSU Campus, Corvallis, OR, Jul 2004.
Vinca sp.
Asclepias speciosa, milk weed. Note opposite leaves and copious white sap seeping from damaged leaf. These are typical flowers for the family. Note the reddish reflexed corolla lobes. The very tips of 2 or 3 sepals are scarcely visible between corolla lobes. Just above the short corolla tube is the whorl of hooded and horned appendages that make up the corona. The green and pink gynostegium is in the center of the flower. One of the five grooves of the gynostegium in the central flower is clearly visible. The pair of pollen sacs and the connecting gland that was present in this area of the gynostegium has been removed by a visiting insect. The gland would have been directly above the groove and it would have been attached to one pollen sac in each of the depressions visible on each side and slightly above the groove. The gland in the next counterclockwise position is still in place and is barely visible on the right side of the tip of the lower right coronal horn.
Asclepias curassavica, blood flower.
Calotropis gigantea, crown flower. The "crown" of this flower is used in leis. The dark gland at each of the 5 points around the massive stigma is attached to two pollen sacs, one from each of two adjacent anthers.
Calotropis procera, small crown flower.
Ceropegia ampliata. Note orientation of hairs in the perianth tube that would make it difficult for insects to crawl out of the chamber once they enter.
Ceropegia haygarthii. Zygomorphic flowers such are this are rare in the family. The corolla on this one has been sectioned to reveal the gynostegium deep inside the tube. The pollination syndrome in this case includes trapping the visiting insect for a period of time. Note the milky sap oozing from the cut surfaces.
Dischidia sp.
Hoya bicarinata, wax plant, pua-hoku-hihi. Vine from S. China with roots appearing along the stems. Leaves shiny, thick; flowers in clusters at leaf axils, fragrant, waxy, used for leis.
Hoya carnosa, wax flower. In this species the corollas are fuzzy and the waxy coronas partially obscure the gynostegium. The glands connecting adjacent pollen sacs are visible as tiny dark specks in the grooves between the coronal appendages.
Stephanotis floribunda. This sweetly scented vine has tubular flowers that hide the gynostegium. It may be seen in the cut-away view in the second photo.  The ant in the third photo is "trapped" on the gynostegium; one leg is stuck in each of two of the grooves.  It is apparently not strong enough to free itself by dislodging the pollinia attached to the glands at the narrow end of the grooves.

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