by Bruce Brethauer
I don’t generally like to write about plants which I have grown for a very short time, as it is difficult to assess their needs through the course of a year, but nevertheless, I have recently acquired a plant of Cissus tubersa, and find it to be such an unusual plant, one which also appears to be so easy to grow that I decided to make an exception here. Cissus is the largest genus of the grape family (Vitaceae), with approximately 350 described species. This is a widespread genus, with species primarily distributed through the tropics and sub-tropics. Many growers may be familiar with several other members of the genus Cissus, including several plants grown as foliage plants, including "Grape Ivy" (Cissus rhombifolia) and "Kangaroo Vine" (Cissus antarctica), as well as several succulent vines, including Cissus quadrangularis, and C. quinquangularis, which produce vines consisting of four and five angled segments respectively. Cissus tuberosa is distinct in that it is a caudicuform - producing massive prostrate stems which can eventually grow to 10 inches in diameter and several yards in length, with additional deciduous vines which can grow to 5 yards or longer during the growing season. The species is native to Puebla, Mexico, where it grows at an elevation of nearly 5000 feet. It usually grows on rocky outcrops where its heavily branched scrambling vines may cover rocks and nearby vegetation. During periods of drought, the annual vines die back, leaving only the massive caudex. While plants in habitat typically produce a horizontal caudex, plants in cultivation can be trained to grow upwards on a trellis or similar support, and should eventually produce a more upright caudex. To date, I have not seen any large specimens in cultivation, so I cannot comment on the general appearance of mature plants, but even young plants with relatively small caudexes are curiously attractive: one of my plants - propagated from a cutting, has produced a twisted, rather gnarled looking caudex, with a few irregular succulent branches with curious swellings at the nodes. The caudex is mottled in green and grey - I suspect that with age, it will become more uniformly grey, and may eventually develop a corky "bark" - but this is only speculation on my part. The foliage is produced at the nodes of the annual vines, with deeply cut leaves looking intermediate between the leaves of a lace leaf Japanese maple and a grape leaf. The vines also produce typical tendrils which enable this plant to attach to other vegetation as it grows. In this species, some of the vines produce irregular swollen segments above the nodes along its otherwise "annual" stems, which can be rooted to establish new plants. Unlike other caudiciform species, these cuttings will eventually produce typical caudexes - the plants of this species do not need to be propagated from seed to produce their characteristic growth. It seems that most plants in cultivation have been propagated by this means alone.
Cissus tuberosa will eventually flower - producing insignificant greenish/yellow flowers which may be followed by small clusters of fruits. The ripe fruits take on a purplish black coloration and may produce a bit of the waxy bloom typical of the common grape. It appears that two clones may be necessary to produce viable seed, because other growers indicated that their plants have never set fruits after flowering. I harvested the seed of my plant, and attempted to germinate the seed. Only a single seedling emerged from this experiment. This plant grew quickly, and within months produced a good sized caudex. I have little additional information on the fruits of this species, but with many other succulent relatives of the grape, the fruits may be unpalatable if not inedible or even toxic - so I would not recommend sampling the fruits of this species.
As with many caudiciform species, this plant will probably grow best when provided with warmer temperatures, long daylight hours, adequate moisture and a rich soil, or (lacking fertile soil), frequent fertilization. Given these conditions, this species will grow rapidly, with the annual vines growing to 6 feet - and possibly to as much as 15 feet, and its caudex increasing significantly in length and width. In cultivation, these vines can be clipped to much shorter lengths to control rampant growth, but this will also slow the development of the caudex. Mike Massara (of Out of Africa fame) has also suggested that some caudiciform species be grown in the open ground, in a soil which has been heavily enriched with well composted animal manures. I attemptedthis experiment with several plants, and can report that while my plants produced significant growth of vines and frequently flowered, I noticed no significant increase in the growth of the caudex in this species.
I suspect that plants should be kept drier and cooler in winter, to induce dormancy. At the outset of dormancy, the plants will likely loose much of their annual growth of vines and leaves; they should be kept fairly dry through the winter months, watering once every two to four weeks to prevent excessive drying of the roots and caudex. No fertilizers should be applied at this time, and the plants should probably be maintained at relatively cool temperatures (to the low 60's or upper 50's - although this species may survive brief exposures to much cooler temperatures than this - possibly to nearly freezing temperatures). In spring, the plants can be watered more frequently, and when temperatures are reliably warm, the plants can be moved outdoors, gradually acclimatizing them to the increased exposure to daylight by moving them successively from shaded sites to more sunny exposures. Once the annual vines begin to be produced, the soil should be kept evenly moist (but not soggy) throughout the growing season - extended drought may result in the plants going dormant (and loosing their vines and leaves) prematurely. If the growth rates of these plants are as I have described them, they will likely benefit from frequent applications of fertilizer during the growing season. I expect that these plants are heavy feeders, and will probably need more fertilization than I usually recommend for other succulents - so mix the fertilizer at about half of the manufacture's recommended strength but apply as frequently as they would recommend for outdoor flowers or vegetables. I prefer fertilizers such as Miracle Gro and Dyna Gro Bloom, but practically any all purpose fertilizer will do, although I would still recommend fertilizers with relatively low percentages of nitrogen (such as the bloom boosters, bulb fertilizers, and fertilizers designed for root vegetables).
While never truly common in cultivation, it is my impression that Cissus tuberosa had once been a slightly more popular plant than it is today - several growers confided that they had grown this plant many years ago and had recently "re-discovered" it. I don’t know if this represents in any way a resurgence in the popularity of this plant, but it is nevertheless an easy plant with an unusual caudex which quickly acquires a certain curious character with its contorted twists and gout-like swellings. It is an exceptionally easy plant which has a potential for rapid growth, making it a good selection for growers who are new to the caudiciforms. Best of all, they are easy plants to propagate, and can be grown from seed, cuttings, and from cuttings taken from the thickened growth on the annual vines, so once established, it is easy to propagate additional plants to share with other growers. Despite its easy going nature, and the ease of propagation, this species is still rather uncommon in the trade - and may be easier to acquire through a local Cactus and Succulent Society, or on e-Bay than through the usual specialist nurseries.
The caudiciforms are not for every grower - they do not have the classic beauty of other succulents, or the geometrical, symmetric growth which many growers prefer in their succulent plants. These are the plants for people who can really appreciate the "ugly ducklings" of the plant world - each plant having its own individual charm - warts and all. If you are looking for a plant with lots of character, but is easy and fast growing, this could well be the plant for you.