Oleander, frangipani, Hoodia those weird potted plants on the “Enterprise” in “Star Trek: The Next Generation” (Pachypodium), all belong to the family Apocynaceae, also known as the dogbane family and the periwinkle family. The family Ascelpiadaceae (milkweed family) has now been included in the Apocynaceae to produce a large group of plants with some weird and varied members.
They're dicotyledonous, meaning that they have neatly arranged vascular tissues in their stems and branched veins in their leaves (those of them that have leaves). They're mostly tropical with a wide variety of trees and lianas as well as small plants and some very strange succulents. Succulents are classified into several main types based on how they store water and most of these are found in the Apocynaceae. Borderline succulents (e.g. Hoya) are only slightly fleshy. Stem succulents (e.g. Orbea) have fleshy stems that are about the same width for their entire length (or at least the fattest part isn't the base). Pachycauls (e.g. Adenium obesum) have stems that are thin at the top and get gradually fatter towards the base. Caudiciforms (e.g. Ceropegia linaris) have thin stems that suddenly get fat at the base or perhaps the fat bit is a swollen root. Some (e.g. Pachypodium lameri) even change from one type of succulent to another as they age. This family is characterized by flowers with five petals and seed pods consisting of two carpels. The pollination mechanism is often complex and likened to that of orchids. People use cats whiskers to pollinate Adenium and Pachypodium. Stapeliads can be pollinated using bent wires and a binocular microscope. The seeds are large and equipped with parachutes for wind dispersal.
The stapeliads are a group of small (mostly less than 30cm tall) cactus like plants sometimes called carrion flowers (because their flowers often smell of rotting meat). They mostly have four sided stems that branch from the base to form clumps.
They are generally not the easiest plants to cultivate, often being prone to fungal and insect pests (in spite of often being poisonous).
Some species, particularly many of the stapeliads, are edible. Some have medicinal properties.
Let's look at some of the more noteworthy genera.
Adenium (desert rose) are pachycaul or caudiciform shrubs and small trees from Africa and Arabia. They have large leaves on new growth and beautiful flowers. They're becoming increasingly common as house plants and there are many cultivars.
Apteranthus (sometimes included in Caralluma) are stapeliads from north Africa with one species (A. europaea) in mainland Spain, the only stapeliad to grow naturally in Europe. They form clumps of four sided stems and have clusters of small flowers near the growing tip. Hardier than most stapeliads.
Ascelpias are famous for being the milk weeds on which the caterpillars of the monarch butterflies feed. Have tuberous roots and clumps of leafy (or sometimes leafless) stems with clusters of flowers. The commonest species is A. tuberosa which grows to 1m high and has clusters of small orange or yellow flowers. A. speciosa with pink flowers is probably more attractive.
Brachystelma are caudiciforms with leafy stems. The flowers often have the tips of the petals united and smell terrible.
Calotropis are tropical shrubs or small trees with large, leathery leaves and flowers in clusters. They are notoriously poisonous.
Caralluma used to be used as a dumping ground for stapeliads that didn't fit in other genera. Consequently it became rather a mess. More recently it's been re-classified with many species being moved to other genera (e.g. Apteranthus, Anglolluma, Frerea) but this doesn't seem to have been generally accepted and the controversy continues. Some species have flowers produced on long spindly terminal inflorescences, which look really strange on cactus-like plants. C. edulis is eaten as a vegetable. C. fimbriata has been used in India in much the same was as Hoodia is used in Africa and has attracted the attention of the medical community with a certain amount of controversy.
Ceropegia is a large, varied genus of borderline succulents, stem succulents and caudiciforms. They have tubular flowers, usually with the petals remaining united at the tips to produce a strange lantern shape. The commonest type in cultivation is C. linaris ssp. woodii (rosary vine), a small caudiciform with long hanging stems, mottled, heat shaped leaves and purple flowers. This is often used as a grafting stock for stapeliads. C. dichotoma has erect, fleshy, stick like stems. C. stapeliiformis looks like a stapeliad with very long, sprawling stems.
Dischidia is a genus of epiphytes. They're mostly smaller than Hoyas and often have strange, inflated leaves in which ants live.
Duvalea is a genus of stapeliads. They're small, even for stapeliads, only growing a few centimeters high, forming clumps of near globular, four angled stems. The flowers are mostly maroon with the petals folded back to resemble spokes.
Echidnopsis (not to be confused with the cactus genus Echinopsis!) is a genus of stapeliads with multi-ribbed stems and small flowers.
Fockea is a genus of large caudiciforms with climbing stems and small greenish flowers. F. edulis is sometimes eaten as vegetable. A plant of F. crispa for a long time held the record of the world's oldest potted plant. Relatively easy to grow.
Frerea is a monotypic genus, the only stapeliad with proper leaves. They also have sprawling, four sided, fleshy stems and small purple and white striped flowers. Being epiphytic, they like more humidity than most stapeliads.
Hoodia, yes the slimmers' new best friend! Some of the larger stapeliads, with clumps of multi-ribed, spiny stems, looking very much like a cactus. The flowers are produced near the tops of the stems and are rather varied in size (the species with smaller flowers used to be included in Trichocaulon).
Hoya (wax flower), epiphytic climbers with long stems, large leaves and clusters of small flowers. H. carnosa is common in cultivation but there are many other species worth growing. The smaller species like H. bella are probably more practical as house plants. The International Hoya Association
Huernia, small stapeliads with flowers that have points, like small petals, between the main petals. Most species have between 4 and 6 ribs. H. pillansii has many ribs and soft, hair like spines.
Larryleachia are stapeliads with many small tubercles, more-or-less globular stems and small flowers. Formally included in Trichocaulon.
Mandevilla is a genus of epiphytic vines with large flowers. M. splendens is becoming a popular potted plant for the patio.
Nerim has only one species, N. oleander (oleander), leafy shrubs with clusters of usually pink flowers.
Orbea, probably includes the most commonly cultivated stapeliad, O. variegata (which is also one of the easier species to grow). Small plants with waxy, four sided stems and a raised ring (annulus) around the middle of the flowers. O. variegata has cream flowers with blown spots. O. cilliata has globular spiny stems and white flowers. O. cooperi has thin stems with a lot of red blotches, and yellow and flowers with red spots.
Pachypodium is a genus of very strange plants. They're stem succulents, pachycaules or caudiciforms with spiny stems and large leaves. The beautiful flowers are produced in a terminal inflorescence (except for P. namaquanum). The best known is P. lamerei, a shrub or small tree from Madagascar that looks like a cross between a palm tree and a cactus. When young, it's a stem succulent with large leaves at the top of its spiny stem. Once it starts flowering, it becomes more of a pachycaule with relatively thin branches and a very thick trunk. The flowers are white. Small species (P. succulentum, P. bispinosum and P. brevicaule) are more practical to grow in colder climates but rarely seen. P. brevicaule, the smallest species looks like a lump of pale green stuff with a few leaves and has yellow flowers. P. succulentum and P. bispinosum are very similar caudiciforms with thin spiny stems and pink flowers.
Plumeria (frangipani, one of few plants where the common name is longer than the Latin name) are small stem succulent trees with large leaves. They have beautiful flowers. Many culitvars.
Pseudolithos are very strange stapeliads, often with solitary, four angled, stems. They're covered in tubercles, which are larger on the angles. The flowers are small and produced in clusters. They look rather like Kushite pyramids and as they come from north East Africa, this might not be a coincidence.
Sarcostemma are sprawling and often climbing shrubs with, stick-like, leafless stems and clusters of small flowers.
Stapelia are stapeliads with clumps of four sided, velvety stems and often large flowers from near the base. S. gigantea has flowers up to about 40cm across, probably one of the largest flowers produced by a plant that's fairly practical to cultivate.
Tavaresia (formally called Decabelone) are stapeliads with clumps of multi-ribbed stems with clusters of three spines at each leaf position (other stapeliads have only one, if that). Have huge, trumpet shaped flowers yellow flowers with red spots.
Vinca minor and V. major are the common garden periwinkles of temperate climates with sprawling leafy stems and usually purple flowers. Among the hardiest plants in the family.
If you want to exercise your green thumb, particularly if you live in a warm climate or want plants for your house or greenhouse, this family offers some interesting choices.
For more information:
Apocynaceae | Facebook http://www.facebook.com/pages/Apocynaceae/108062845893916
International Asclepiad Society http://www.asclepiad-international.org/
The Ascelpiad Page http://www.succulent-plant.com/families/asclepiadaceae.html
Stapeliad :Stapeliads and other Ascelpiads list http://tech.groups.yahoo.com/group/Stapeliad/
Forum on Adenium and Pachypodium http://tech.groups.yahoo.com/group/ADENIUM/