Sometimes also known as succulent sesame, because it is related to that herb, the small and thick-stemmed tree usually grows no taller than 10 feet, but can reach 24. The yellow, 2 to 3-inch, five-lobed, purple-throated flowers of one of the most popular varieties--Uncarina grandidieri--resemble those of the black-eyed susan vine (Thunbergia alata) on steroids. They are backed up by deceptively velvety heart-shaped leaves edged with red. Uncarina decaryi is similar but with more deeply cut foliage.
I call the leaves' softness deceptive because the plant also harbors sticky 1 ½ to 2-inch horned seed pods with tiny barbed “fish hooks” at the end of their horns. Those hooks allow the pods to latch onto large animals for a free ride, but reportedly can catch small animals--such as mice--as well. Obviously, you do not want to touch those pods unless you are wearing heavy gloves, or unless you have plenty of time to pick nearly invisible barbed thorns out of your fingertips!
Native to Madagascar, uncarina requires care similar to that of the desert rose (Adenium obesum). Give it a clay pot, the type of potting mix intended for cacti, and plenty of sun and water during its blooming season of spring through autumn. Then allow it to remain almost dry over the winter. It may drop most or all of its leaves during that dormant spell.
Those of you in USDA zones 10 and up might be able to grow uncarina outdoors, in sandy, alkaline soil in full sun. I wouldn't try that if your winters are excessively wet, though, since the little tree is susceptible to root rot.
Please don't get frustrated if you find yourself unable to hand-pollinate the flowers. In the plant's native habitat, that job is carried out by beetles who have to chew up the anthers a bit to get at the gluey pollen inside their lobes. So, instead of wielding an artist's brush, try squeezing the anther's lobes as if they were toothpaste tubes.
If you wish to sow uncarina seeds, dunk them briefly in a bleach/water mix – such as 1 part bleach to 9 parts of water -- before planting them in a damp and sterile combination of seed-starting mix and sand. Cover them with about 1/5 inch of that mix and keep them in a warm position until they begin to germinate in two weeks.
If you don't like yellow, the flowers come in violet-pink (Uncarina abbreviata and stellulifera) and white (Uncarina leptocarpa) versions as well, though I'm guessing those may be harder to find.
Despite its snagging seedpods, succulent sesame reportedly is a highly attractive, free-flowering, and easy-care houseplant, which doesn't mind dry indoor conditions. Theoretically, you should be able to prevent those pods from forming by keeping beetles and other chewing insects off the plant. If one of the prickly fruits latches onto you despite all your precautions, try the “Open, Sesame” command. Hey, it worked for Aladdin!
Photos: The Uncarina decaryii photo is by Frank Vincentz, courtesy of Wikimedia Commons and this license. The thumbnail Uncarina grandidieri photo is by Kelley MacDonald, Uncarina stellulifera photo by Indigoez, and Uncarina roeoesliana seedpod image by SallyD, all from the Dave's Garden PlantFiles.