| Cucumbers and Gourds—Succulent Cucurbits
By now we all should realize that succulents have independently evolved in a number of plant families. In some of these families, such as the Cactaceae or Crassulaceae, almost all—or at least a high percentage—of the species are succulents. Many other families have a number of genera and species adapted in one way or other for retaining water during times of drought, and some families may have only one or two succulent species. Some of the families composed largely of succulents seem fairly exotic, filled with plants well known by collectors, but hardly familiar to the average person. The gourd family, Cucurbitaceae, however, is familiar to anyone who has ever eaten a cucumber or a cantaloupe. In addition to the large number of species cultivated for food, however, a good number of cucurbits have adapted for life in areas with extensive dry seasons or uncertain weather conditions. Succulence has shown up a number of times in this family and occurs in genera scattered around the world, the largest number from eastern and southern Africa and Madagascar, but a quite few from the New World as well.
Typically, succulent cucurbits consist of a large tuber out of which a thin stemmed clambering vine arises at the beginning of the growing season. In the wild many of these tubers remain underground, while others protrude partly above the surface, or are almost completely above ground. Those tubers that stay below the surface generally have a smooth surface, while the above ground ones often develop a more woody exterior, with fissures and protuberances that most succulent enthusiasts would say give them a more interesting appearance. The leaves vary considerably among the different genera, in some having an entire, rhomboidal, rather ivy-like shape, while in most species the leaves are more or less dissected, sometimes quite finely.
With some of these plants the distinction between a succulent caudiciform, and just a vine with an underground rootstock grows quite fuzzy. Marah, the California native sometimes called “manroot,” with an occasionally huge underground tuber, approaches the boundary of what are generally considered succulents, but I don’t know of anyone who has bothered to cultivate them as a container plant (perhaps because of their rampant growth as much as anything), and few people think of them as more than a kind of wild cucumber. The closely related Dieterlea fusiformis, more amenable to cultivation because of its smaller proportions, is considered to be a succulent, really with no greater justification.
Most of the tuberous cucurbits in cultivation come from Africa, with Kedostris , Momordica and Gerrardanthus probably being the best known genera. The caudex of the South African Kedostris varies in shape from a rough-textured approximate sphere to a greatly flattened body, almost like a disc. It has the typical finely dissected leaves, quite small and multi-lobed, produced by a vine that can grow to several yards in length. Generally similar in regard to caudex, the slower growing vine of Momordica (from east Africa) puts out entire leaves, with a fresh green, almost shining texture, quite attractive and different from most of its relatives. A number of other African genera share the characteristics of Kedostris, a more-or-less rounded caudex, often marked with bumps and irregularities, and three or five or seven lobed leaves growing from a fairly large, thin-stemmed vine. Several of these have come into cultivation in the last ten years or so, among them species of Coccinia and Corallocarpus, along with members of several other genera. These plants, however, tend to be very much alike aside from details of their small, odd-shaped flowers. In contrast, Gerrardanthus, in cultivation for years but nonetheless not that common, has entire cordate (heart-shaped) leaves and a spherical caudex tapering up almost like a pear. More of these caudiciform plants are entering into the trade, and though they’re certainly worth growing, their exotic-sounding names perhaps bring more attention than is really justified .
Ibervillea, the New World equivalent to the more interesting caudiciform cucurbits from Africa, has a number of species, the best known of which, Ibervillea sonorae, has an above-ground, rather woody caudex that stretches out to the point from which its vines emerge. This point doesn’t have to be in the center of the caudex, and specimens of I. sonorae often have strange, sloping, asymmetrical bases that give them an eccentric and distinctive quality. The tubers of the other ibervilleas (I. tenuisecta is an example), some of which grow as far north as Texas, tend to stay underground, and as a result, have less texture.
Madagascar has its own succulent cucurbits, and the most distinctive occur in two small genera. Though both Seyrigia and Xerosicyos eventually (after many years in the case of Xerosicyos) form somewhat tuberous bases, they are generally valued for their odd stems and leaves. Actually, Seyrigia doesn’t have leaves, but rather belongs with that group of succulents jokingly referred to as “dead sticks;” plants with somewhat thickened stems, that conceal their chlorophyll behind a screen of other colors, and look like a mass of barren twigs. These plants, though quite interesting, appeal only to a fairly specialized audience. One seyrigia, though, S. humbertii, has stems so densely covered with soft white fuzz that the plants look as if they’re made of felt. Xerosicyos has ordinary stems, arrayed with remarkable yellow-green leaves the size and shape of coins. X. danguyi, the more common one in cultivation, has leaves as big in diameter as silver dollars and twice as thick, while the rare X. perrieri has slightly thinner leaves the size of quarters. In the wild these plants clamber over trees in dry places, but in cultivation their perennial stems grow fairly slowly, in contrast to some of their more rapidly vining relatives.
A number of more-or-less succulent cucurbits, possibly not in cultivation, grow in the dry northwest of South Africa, including Acanthosicyos, with the standard big tuber, but stiff, spiny branches that sprawl rather than vine, and large melon-like fruit (quite bitter) that look oddly out of place in an arid wilderness, like watermelons growing in the desert. Finally, in common with so many other spectacular endemic succulents from Socotra (that smallish island between Somalia and Yemen), Dendrosicyos socotrana grows into a thick-trunked, pachycaulous tree close to twenty feet tall and four or five feet thick. Though certainly the most spectacular succulent in the Cucurbitaceae, it remains extremely rare in cultivation, commanding high prices when it does show up.
The caudiciform cucurbits do well in cultivation, though finding any to purchase may be a problem. Since they essentially are climbing or clambering vines, they don’t need as much bright light as many free-standing succulent plants. Any standard succulent mix should work fine as soil, though a little more organic matter than average can’t hurt. Most of them come from places where it never freezes, so outdoor culture won’t work, but in a greenhouse or a bright window they’ll do well. Start watering them regularly when they begin to vine (in some forms of Ibervillea sonorae from Baja California, this may be in winter), and when the vine dies back, reduce (but don’t eliminate entirely) water, to about every three weeks will do during this dormant time. The stem and leaf succulents from Madagascar respond well to the same treatment. As far as Dendrosicyos socotrana goes, if you find one let me know how it does (actually, it presumably would do well with the same watering schedule, but considerably brighter light).
The Garden has a good collection covering many of the succulent genera in this family. Not many growers will feel the need for a comprehensive collection of these plants, but everyone who likes the exotic in xerophytes should try one or two.
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