by Bruce Brethauer
The genus Ceropegia includes about 200 or so species of predominately vining, shrubby to sub-shrubby plants of the tropics and subtropics. The greatest diversity of species originates from Africa, Madagascar and the Canary Islands. Many of the species exhibit at least some degree of succulence, either producing succulent stems, leaves, and/or tubers and caudexes. Most are adapted to regions with seasonal drought, and will tend to loose leaves, or in extreme cases, even stems to limit moisture loss during extended drought, or when plants are otherwise stressed. During the rainy season, most species will produce a flush of growth, and will typically flower at about this time as well. Ceropegias are members of the Asclepiadaceae, or milkweed family, and like other members of the family, will produce the characteristic fruits ("pods"), and the seeds with silken "parachutes" similar to other milkweeds, but their flowers are amongst the most unusual of the family, typically producing long tubular flowers with a bulbous base, and ending with 5 highly modified corolla lobes, whose tips may be fused together to produce an egg-beater, or birdcage-like structure. In some species, the corolla lobes are said to resemble parachutes, lanterns, and parasols. Linnaeus himself had one of the more curious associations, likening the appearance of the flowers to a fountain of wax: he derived the name "Ceropegia" from 'keros' meaning wax and 'pege' meaning fountain.
As a rule, the flowers are not particularly colorful; in many species the flowers are greenish-white with purplish spots and streaks - but their unusual forms more than make up for their limited palettes. The flowers are actually traps which capture insects - sometimes imprisoning then for up to several days. But these flowers are not carnivorous, instead, this is a strategy to help insure that any insect which is lured into the flower will eventually transfer pollinia to the receptive stigma lobes. The flowers of the Ceropegias produce scents to attract very specific pollinators. While not as foul scented as many other members of the Milkweed family, the Ceropegias typically have scents which are less pronounced, although still curious; Ceropegia cimiciodora for example, has a scent reminiscent of a dead bed bug. The scents, flower colors, and "hairy" corollas of some species essentially may mimic animals to attract flies to their flowers. These flies push their way past the corolla lobes, and work their way down the floral tube to the bulbous base of the flower, which typically contains the stigma lobes and anthers. The elaborate structures of the corolla lobes will only admit insects of a specific size, and will also help to prevent any premature escapes. The floral tube bears numerous downward pointing hairs which also prevents insects from climbing out of the flower. In trying to find an exit from the flower, the insect will inevitably encounter the stigma lobes, and will also blunder into the anthers, picking up one or more of the pollinia - waxy packets typically containing hundreds, if not thousands of pollen grains.
In time, the downward pointing hairs in the floral tube will become more flaccid, and the petioles which once held the flower upright when the flowers first emerged, will tend to droop, leaving the flowers hanging upside down, giving any trapped insects an opportunity to escape. It is only when the escaped insects enter into a second flower (possibly becoming trapped a second time) that cross pollination can occur. As with most species of the milkweed family, the various species of Ceropegia tend to resist self-pollination, so that, more often than not, at least two genetically distinct individuals are needed for successful pollination - otherwise plants may be unlikely to set seed.
Ceropegia woodii is at once one of the most attractive, and one of the less typical species of the genus. While most of the Ceropegias produce rather nondescript foliage which is typically lost during periods of drought, Ceropegia woodii produces attractive, heart-shaped, succulent leaves which are beautifully marbled in silvery green and are more or less permanent. Unlike many other species in the genus, which may produce long scrambling vines, which in cultivation can twine extensively through other plants in a collection, this is a relatively compact trailing species with thin, wiry stems. The vines do not typically climb - they produce no tendrils and seldom twine their through other plants for support, so I suspect that in habitat, Ceropegia woodii is a scrambling, ground hugging vine. In cultivation, plants are frequently grown in smallish pots, with their long stems cascading over the sides. In time, the vines may grow to several feet in length, or they may be kept more compact by periodically clipping excess growth. The cut sections of these stems can be set on top of a moist potting medium to establish new plants, but new plants may also be propagated from small tubers which are sometimes produced along the stems. It is also possible to establish a new plant by rooting a single leaf. While it is possible to propagate plants from seed, I am not aware of anyone who has tried this, as it is far easier to propagate plants from cuttings and tubers.
The flowers are fairly small, measuring to about 3/4 inch (2 cm) in height, and are tubular with a large bulbous base. The corolla lobes are united at their tips, and are covered with dense hairs. These flowers are of a greenish to brownish purple in coloration, and the corolla lobes are typically of a purplish to a dark maroon coloration. The flowers are surprisingly cryptic - their small size and rather dull coloration makes them a bit hard to distinguish when the plants are observed casually, which is unfortunate, as they truly are quite exceptional - if you ever see a plant in bloom, try to examine the flowers under a magnifying glass to truly appreciate their unusual form. Better still, if you have access to a dissecting microscope - examine the flower under its higher magnification, and if you are able, cut the flower lengthwise and examine its interior under magnification to better appreciate the insect trapping adaptations of this and other Ceropegia species.
Plants are best provided with bright but filtered light, warm temperatures, an evenly moist (not wet) growing medium, and fairly high humidity. In spite of its rather delicate appearance, this is a tough survivor, easily tolerating long periods of benign neglect. My general instructions for growing succulents may be a useful starting point for this species, but I have found that it will grow better if the plant is not subjected to extended drought - particularly when the weather is warm and the plant is showing new growth. While it is very drought tolerant, if you treat it too much like a denizen of the desert, this species will stop growing, and its leaves may begin to shrivel, or (in extreme drought) the leaves may even drop. I tend to water it somewhat more frequently than other succulents in my collection, but even so, it is best to allow the soil to become dry before watering, but when you do water, give this plant a good drink. Choose a well draining potting medium which is fertile. This can be a fast growing plant when conditions are right, so it will benefit from a richer soil and somewhat more frequent fertilization than some other succulents - but do not use standard potting soils which tend to stay too wet for too long: you may modify a standard potting soil by adding additional grit, pumice, or Perlite to provide additional drainage. I have also grown a plant under conditions more suitable for growing orchids (warm, with moist and humid conditions) with surprisingly good results. In this experiment I grow my plant in a medium of chopped coconut fiber (coir) and cork bark, - a medium which allows for good penetration of of oxygen to the roots. In my experience, this species does not tolerate full exposure to sunlight as well as other succulents in my collection, so if you are in the habit of moving your plants outdoors in the summer, this species may benefit from a bit of dapple shade - especially during midday heat. In winter, this plant will probably benefit from somewhat cooler and somewhat drier conditions. Ceropegias from other regions can be cold sensitive; most species do not tolerate frost, and many may not survive extended exposure to very cool temperatures, so it may be best to maintain this plant at 60 degrees, or warmer, through the winter months.
Ceropegia woodii is very resilient: even if subjected to conditions which result in significant losses of vines and leaves, it can easily be revived by providing more optimum conditions, and in short order, will be thriving again. Even plants which have lost all of their leaves may be re-established by growing the small tubers which are frequently produced at nodes along the vines. Under favorable conditions, these will readily sprout new vines. So, unlike some succulents, which may tend to accumulate permanent "battle scars" from improper growing conditions, a "rejuvenated" Rosary Vine may show little evidence of past indiscretions.
The marbled foliage and unusual flowers makes Ceropegia woodii one of the most attractive species of the genus - it is also one one the most frequently grown species as well, as it is easy to grow, and is compact enough to be grown in a small pot hung next to a bright window. It is frequently sold as a houseplant at nurseries and home and garden centers so it is also one of the most readily available species of this genus. When it is happy, this is a fairly fast growing plant, adding many inches of growth to its vines each summer. There are very few downsides to this plant - it is forgiving in its requirements, it lacks thorns and spines, and it can be maintained in a fairly small pot: but if you insist on a plant with large showy flowers, this may not be the best plant for you. It also bears mentioning that other members of the milkweed family have the tendency to produce toxins in their tissues and sap. I do not know if this species is toxic, so if this is a concern (if you have pets or young children which may accidentally ingest any portion of this plant) it may be wise not to grow this species, or if you do, try to keep it out of their reach, just in case. Otherwise, this is an exceptional plant, and is, in my opinion, one of the finest of this genus.