The nights have started cooling off, so it is time move my tropical plants back into the greenhouse before we have our first frost. I thought I’d snap some pictures of a few interesting specimens before I put them away for the winter.
At first glance Adenia globosa looks distinctly alien–definitely more so than the hybrid Paphiopedilums that they invariably seemed to use as stand-ins for alien flora on old Star Trek The Next Generation episodes. When examined more closely, however, its anatomy starts to make sense. Adenia is a genus in the Passifloraceae, the passion flower family, and like our native Passiflora incarnata (maypop), many Adenia species are leafy vines with tendrils that help them to climb other plants. A. globosa has evolved in the arid savannas of east Africa, so its features reflect that history.
The base of the plant is swollen into a more or less globular trunk to store water.
With no need to climb other plants, the stems are rigidly erect or arching, and the tendrils have been modified into stout thorns to protect the plant (and its stored water) from herbivores. New stems have a single, tiny leaf under each thorn. The leaves soon fall, so the majority of photosynthesis is carried out by the stems, which are less subject to water loss than large leaves would be.
Old stems develop a glaucous coating that probably serves to further protect them from sunburn and water loss.
A. globosa seems reasonably easy to maintain, given warm temperatures, bright light, and very well drained potting media, but growth is very slow. My plant has just about doubled in size over the past seventeen years. Some succulents (e.g. Pachypodium) develop the best form and character when underpotted, but Adenia seem to grow fastest when somewhat overpotted. Some growers have had good luck using large tubs or raised beds to get plants to the desired size before moving them to smaller display pots, but great care must be taken not to over-water when using large pots.
A. globosa is dioecious, so separate male and female plants are required for seed production. My plant has never flowered, so even if I had a second specimen, seeds would be entirely hypothetical. Cuttings will root relatively easily and slooooowly produce a swollen trunk. Patience is definitely required for all aspects of A. globosa cultivation.