O. decaryi is, like many other of my favorite plants, from the island nation of Madagascar. Highly prolific French botanist and taxonomist, Joseph Marie Henry Alfred Perrier de la Bâthie (1873-1958), first described the plant in 1944.
O. decaryi was named after Raymond Decary (1892-1973), a French botanist and anthropologist who studied all things related to Madagascar—not just plants. In fact, there are hundreds of plant species named after him while Madagascar was under French colonial rule.
O. decaryi is available in cultivation from many dealers, but I wouldn’t say it’s common. Still, if you go to your local succulent/cacti show, you have a good chance at finding a specimen. You may also find it online, but beyond that it’s quite rare.
The plant lends itself to bonsai forms quite naturally and, with some pruning, can become a stunning specimen.
Without pruning, it will grow into a tree and in time develop a rather bumpy surface, hence the common name “Elephant tree” for resembling the skin of an elephant. The leaves are odd-pinnate, petite, and have a waxy finish to them and because they are small, they naturally enhance the plant’s bonsai aesthetic. The leaves will often turn red in periods of dormancy or drought. Overall, it’s a beautiful, winding tree and doesn’t require a lot of care. You can keep it small with annual pruning, or allow it to develop into a proper tree.
I hear that it’s possible for the plant to flower and, thus, bare seed. Allegedly this occurs in the winter and the flowers are exceedingly small. But it’s relatively rare and probably even rarer in cultivation.
There was one time I bought some seed from Holland and planted them all. In the end I received a stunning 0% germination rate. Something tells me that seed starting this plant is rare and impractical. Or that I was sold some serious duds (honestly they could have sold me random seeds and I would have not known as I’ve never seen the seed before).
The more practical method of propagating this caudiciform is to break off a piece of its winding, tuberous root. My O. decaryi have produced roots that bulge in various parts. I usually break off one of these tubers and put it in it’s own 4-inch pot with a piece of the root sticking out of the soil. In about 3 weeks time, assuming you’ve done this in the growing season (I did this around March in Texas), you will start to see tiny leaves forming off the tip. The leaves themselves are beautifully complex, and it’s enjoyable to watch them develop out of a root that looks like a small potato. Do this in spring or early summer while the plant is waking up from its winter dormancy, otherwise they may rot.
If you have a strong mother plant, you can keep breaking off pieces of root/caudex and keep propagating. It doesn’t seem to harm the mother plant. It may stunt it’s growth for the season, but not by much.
I’ve never seen any pests at all on this plant. In fact, a praying mantis attached an ootheca (egg case) to one of my O. decaryi! My guess is that it provides many perfect, lateral branches that they desire along with the fact the plants are small and close to the ground.
It’s quite a strong plant, and because it is grown in rather harsh conditions, it is a relatively adaptable species. It does not need an enormous amount of water, but during the growing season it can enjoy quite a lot of water and be perfectly content. Its roots will swell underneath the soil and you’ll only know that’s the case when you repot the plant.
Some cultivars will completely defoliate in the winter, while some will retain their leaves (semi-deciduous). Regardless, in both states, avoid watering during periods of dormancy.
As this plant grows in Madagascar, it is not frost-tolerant (though I’ve never tested that). It’s growing season is in the spring and summer, and as mentioned, will go into a period of dormancy.
Like most caudiciforms, this plant enjoys a fast draining potting medium. Avoid peat if possible and amend soil with drainage material such as pumice, expanded shale, perlite, or a similar product.