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Euphorbia—Part 6
Let’s move north from the southern parts of Africa, and see what odd twin-spined euphorbias we can come up with. We could go either to the east or to the west. Following the Atlantic, west coast of Africa for several thousand miles will finally take us to countries such as Nigeria and Cameroon, places we associate with tropical forests. But in scattered pockets of semi-arid mountains and plateaus we might find a few very unusual succulent spiny euphorbias as well.
Seasonally dry regions of much of the surrounding countryside provide habitat for a number of shrubby, thicket-forming, or small arborescent euphorbias not unlike those of southern Africa, although often with larger, more persistent leaves. Some of the more striking of these include Euphorbia teke and E. sudanica. Coexisting with these more or less familiar forms, however, is a continuum of obviously closely related, extremely distinctive plants.
Perhaps the best known of these (though all of them are still quite rare in cultivation) is Euphorbia poissoni, like most of them, ultimately a fairly large shrub, freely branching from a central trunk. Its thick stems are covered with tubercles shaped like upside down teardrops, the point at the bottom consisting of a solitary spine (presumably the fused product of originally twinned spines). At the tips of the branches the plants put out a few fleshy, somewhat wedge shaped leaves, sometimes with a bilobed appearance and of a bright green color that contrasts markedly with the grayish-white of the stems. E. unispina, from the same general region of West Africa, from Ghana east to Togo, differs in its greenish (rather than reddish) flowers and the presence of a few small teeth at its leaftips. In addition, although the stems of E. unispina have tubercles similar to those of E. poissoni, these tubercles quickly decompose, leaving cylindrical stems of smooth gray-white. Obviously, these differences are minor, and both of these species may be merged with the generally similar E. venefica, from farther east, into the southern Sudan, Uganda, and southern Ethiopia.
Another related species, Euphorbia sapini, perhaps even rarer in cultivation, is more delicate and smaller growing, with thinner stems and lanceolate leaves. It grows farther south, ranging from Cameroon through the Congo all the way to northern Angola. These interesting species grow very slowly, and cannot withstand much cold. In particular, E. sapini, despite coming from areas characterized by dense vegetation and jungle, seems to require almost complete drought in winter. It’s even slower growing than its relatives and must be kept warm. The others need a more-or-less strict rest period after their leaves drop (which may take place at various times of the year, sometimes more than once a year), until new growth begins. This small group of tropical species doesn’t look like any of the other succulent euphorbias and a well grown specimen of any of them will draw experienced growers like a magnet.
Far from the home of these spectacular, leaf-tipped, gray-stemmed species, Somalia, on the north-east coast of Africa, has more than enough unique euphorbias of its own. Along with more typical, bushy, thin-stemmed spiny species, some tall tree-types and a few very odd, dwarfed, leafy plants that somewhat resemble South African species such as Euphorbia bupleurifolia or E. clava, Somalia also supports a large number of unique twin-spined species that have appropriated many of the forms of the strangest and most interesting euphorbias from every section of the genus. Several Somali species (and a few from nearby parts of Ethiopia) have taken on a form somewhat reminiscent of the medusoid species of South Africa. These plants produce a short, thick central stem, surmounted by a somewhat symmetrical tuft of branches. Euphorbia monacantha, from Ethiopia develops this form, as does the closely related (if not identical) Ethiopian plant known for years simply as Euphorbia “Mrs. Ash,” equally easy to grow. More exotic Somali versions on this theme include the yellowish, somewhat larger growing, E. xylacantha, with contrasting gray spine shields, and the pink-red and yellow-green stemmed E. schizacantha, with spines that fork at their tips. Many of these Somali species have these strangely colored stems, yellow, mottled gray, pinkish, no doubt enhancing their survival prospects in the oddly colored, bleached, often gypsiferous soils where many of them grow (in less than ideal light, of course, the stems fade to various shades of pale green).
Another group of twin-spined Somali euphorbias has taken on the look of the mounding, cushion-forming South African plants. These include Euphorbia mitriformis, E. mosaica, and to a certain degree, E. sepulta. All these are low, densely branching plants, composed of masses of small individual stems. E. mosaica forms a near solid low mound of sparely spined stems; with E. mitriformis the mounds are a little less dense and hump up more in the center; while individual stems are somewhat spinier with the spine shields more distinct. E. sepulta forms a low, less regular, mound, and the spine shields on its branches more-or-less merge into longitudinal ridges. E. dasyacantha forms a small, spiny shrub with odd, yellow-gray stems, while the short stems of E. phillipsiae and the taller ones of E. phillipsioides produce spines of distinctly different lengths, arranged almost randomly.
Other Somali species also make mounds, often more or less dome-shaped, and these include rarities such as E. leontopoda (looking somewhat like a miniature E. groenewaldii), the spiny, densely branching E. atrox, and the somewhat larger, gray-stemmed E. perarmata and E. ponderosa. These plants, with their colorful, stocky stems, look almost like some of the sarcocaulons (now Monsonia), the extreme succulent representatives of the Geranium family from far away Namibia and Namaqualand. E. longispina, with thin stems and aggressively long spines, resembles a smaller but somehow more fierce and desperate E. grandicornis.
Euphorbia immersa forms a little shrub composed of several square-sided branches, but its swollen underground tuberous root dwarfs its above-ground parts. E. columnaris (possibly extinct in the wild because of habitat degradation), has spines shaped like tiny cow horns and stems somewhat reminiscent of a greatly elongated E. sepulta. It sometimes takes refuge on the very edge of crumbly cliffs, where it grows into a narrow upright column several feet tall eventually bending and arching into space. Euphorbia horwoodii passes through several distinct phases of growth. It eventually forms a small mound similar to E. perarmata and E. atrox, but it begins life as a nearly spineless, beige to orange, almost perfect sphere, and then, as it begins to develop branches, looks like a miniature starfish or Christmas ornament. This intermediate phase is so bizarre that it’s a pity it ever grows out of it. The tiny E. turbiniformis, on the other hand, never moves past the spineless, spherical stage, like an inch and half in diameter, pale brown Euphorbia obesa. E. gymnocalycioides, from Ethiopia (and a relatively well watered habitat, receiving as much as 12 inches of rain a year) also forms a sphere, but one with longitudinal rows of little protruding “chins,” (like Gymnocalycium, the cactus genus from which it derives its name), each equipped with a barely visible pair of residual spines. Euphorbia multiclava forms a short, thick, erect stem, oddly ridged and with a few stocky branches, apparently where the main stem simply decides to split into halves. Finally, Euphorbia piscidermis (“fish-skin”) has tubercles and spines modified into what looks like a pattern of tiny, bright-white, diamond shaped scales. The only other plant that remotely resembles this odd euphorbia is the equally strange Turbinicarpus valdezianus from the Chihuahuan Desert of northeast Mexico.
As a group (and there are numerous additional species) the Somali euphorbias are true oddities of nature, derived from the ubiquitous, often nondescript twin-spined euphorbias of the kind that occur all over countries such as Kenya and Tanzania. A few of them, such as E. phillipsiae and E. phillipsioides, grow about as easily as typical small twin-spined plants; in a rapid draining succulent mix, with bright light, protection from temperatures much under 50 degrees, water once a week during the warm months and every three or four weeks in winter. E. gymnocalycioides, though much rarer (and more expensive), grows relatively easily with the same treatment (it also prefers just a bit of shade).
A few of the others, such as E. leontopelma, respond well to a somewhat leaner mix and more dryness in winter, but grow well enough, as does E. sepulta, E. mitriformis and, rather surprisingly, the always coveted E. columnaris.
Species such as E. immersa, E. perarmata, E. atrox, E. schizacantha and many of the others mentioned here have the distressing habit of rotting if given water in winter. Fortunately, even small plants can withstand several months of complete drought. I’ve been nursing a plant of E. multiclava along for decades, and it survives with bottom heat and an extremely lean mix, but I can’t say it has ever thrived. E. piscidermis is generally grafted onto a hardy species such as E. resinifera, and grafted plants will do well for many years; I’ve never seen one grown successfully on its own roots, though I don’t doubt that someone, somewhere, has managed to accomplish this feat. E. turbiniformis was introduced in the ‘70s with tremendous fanfare as about the strangest thing anyone had ever seen, and, as far as I know, not a single one of these plants has survived. Grafted specimens are still being produced, and even they can be difficult to keep alive.
Neither the tropical species nor the Somali plants are really suitable for novice growers. Just finding them can be quite a challenge, and paying for them can be just as challenging. They are some of the most remarkable members of a remarkable genus, however, and anyone interested in euphorbias should try to become acquainted with some of these very rare plants.
The Garden has a few Somali plants—it could use more. At the moment we don’t have any of the West and Central African species, but hope, at least, springs eternal in the heart of the succulent grower.
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