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Succulent Euphorbias--Part 4
After discussing the medusoid species, the leafy and tuberous species, and the relatively unmodified species of South African succulent euphorbias, we’re still left with a great assortment of other plants, occurring in a wide diversity of forms, from a wide range of habitats. One of these sub-groups, the twin-spined euphorbias, extends all through continental Africa and far beyond, and they’ll be the subject of next month’s column. So what exactly are we left with for this one? Well, we have some of the most cactus-like species, some of the most horticulturally popular plants, some of the easiest to grow outdoors, some of the nastiest and some of the “nicest.”
The first several plants, however, are neither the “nicest” nor “nastiest.” They’re among the more interesting of the bunch, however, and as a subgroup of the genus deserve more recognition than the typically receive. There are the plants known as the “finger flowers,” a half dozen species defined by the elongated, finger-like processes on the glands that surround their central flower parts. As a group, euphorbia flowers are never likely to win first place at a major flower show, but they do display a surprising amount of variety for those willing to take a close look at them. Though lacking the color range of the medusoid euphorbias, the frilly processes of the finger-flowers, prominently displayed on long peduncles in some species, give an extra attraction to these plants. Their primary attraction, of course, is their basic morphology, and these euphorbias rank right up there with the other groups when in comes to strange appearance. Euphorbia globosa and E. ornithopus may be the most commonly grown, and often in cultivation the two species look very similar. Both generally form a mass of small, somewhat elongated, jointed green stems with a central stem that imperceptibly turns into a thickened root. In the wild, however, or grown under conditions of very bright light, the resemblance disappears, as E. ornithopus retains its appearance while the segmented branches of E. globosa become as round as marbles. In the wild, as E.globosa matures, its main stem descends steadily farther underground, pulling the older branches along with it, while new branches keep developing on top, resulting in an extremely low-growing plant that looks like a patch of oversized green peas staking out its turf up to eight inches across. In a pot, the main stem and older branches can only go so deep, and the mounds of new branches pile up on top of each other, with more elongated secondary stems that produce the long-peduncled finger flowers uppermost. E. ornithopus, and two of the other species, E. tridentata and E. wilmanae, grow in much the same manner, but with tapering, cylindrical, more obviously tuberculate rather than spherical segments, the differences between the three consisting mainly of flowering details and density of underground stems and tuberous roots. The two remaining members of the group, E. planiceps and E. polycephala contrast by having a single, large, mostly underground stem that branches and rebranches into an almost solid mass of tiny, ground level, secondary stems. The branchlets in E. polycephala are more-or less rounded , but more densely packed together than with E. globosa, while the even smaller branchlets of E. planiceps taper a bit at their tips, as is the case E. ornithopus and the others, but rather than a mass of branches, each plant of these two euphorbias looks like a single solid green clump. Imagine a piece of broccoli, with its florets cut flat across on top (and bigger, up to a foot or more in diameter), and you’ll have an idea of how these two euphorbias look, at least in the wild. In cultivation it’s hard to keep the plants compact enough, and they all tend to resemble the tangled masses of elongated stems of E. ornithopus. E. globosa, at least, is hardy outdoors here if given excellent drainage, and when grown in the ground in full sun the elongated branches of container-grown plants will gradually be pulled underground, to be replaced in time by perfect little green spheres. E. planiceps and E. polycephala are rare enough that I don’t know anyone willing to risk them outdoors to see if they’d survive.
Another small subset of euphorbias develops into forms which resemble the finger-flowered species, but these euphorbias have simple flowers, without the elaborated outer processes of the preceding group. These plants include species such as E. pseudoglobosa and E. juglans, with rounded secondary stems, and E. tubiglans and E. jansenvillensis, with more cylindrical stems (and a relatively huge tuberous main stem/root in the case of E. tubiglans). Included with these species, though not really resembling them, E. susannae has a main stem, somewhat ribbed and with tubercles in the form of sharp (though not dangerously so) little teeth. As E. susannae matures it produces many secondary stems identical to the main stem, which, if taken off, will root and grow into complete plants themselves, little hemispheres of bright yellow-green or kelly-green toothed stems. Unlike the finger flowers, these euphorbias don’t become distorted or etiolated in cultivation, and E. susannae in particular is a very popular plant among collectors. None of these species becomes large, and a four or five inch pot will easily contain a mature specimen of any of them. A note of caution, however: the sap of E. tubiglans, and possibly several of the others, is quite toxic, and I can attest to how miserable even a tiny drop can feel if you manage to get it on your face. Since the plants are completely unarmed, it makes sense that their sap would have good defensive characteristics, but euphorbias seem quite unconcerned with rational consistency, as some of the most poisonous species are heavily armed with sharp spines, and some spineless species have barely, or completely non-toxic sap.
Closely related to these sometimes nasty species, Euphorbia obesa and E. meloformis might qualify as the nicest euphorbias, popular in cultivation since their discovery centuries ago. E. obesa, in particular, is a perfect little ball, almost completely round for many years, divided into symmetrical ribs marked by stitching (almost like a baseball), and with gothic-arch shaped bands of purple and green marking its body. As these monoeicious (either and only male or female) plants grow older they become more cylindrical, the males elongating more than the females. E. meloformis has a generally similar appearance, but its ribs are much more distinct, causing it to look segmented. It often branches when old, and its persistent dried peduncles (flower stalks) make it seem less neat and symmetrical than E. obesa. E. valida, contrary to its name, is so similar to E. meloformis that it may not really be a valid species at all, while E. symmetrica, if not just a form of E. obesa, is the roundest of all, with a height never exceeding its diameter. These plants look like specialists for the most arid of habitats, but surprisingly both E. meloformis and E. obesa will do well in Bay Area rock gardens with excellent drainage, and their stripes and bands of color will be more pronounced compared to container grown plants.
Another set of euphorbias consists of clumping species with cylindrical, ribbed stems, characterized by persistent peduncles that take on the form of protective spines. Several other euphorbias from various sections of the genus also retain peduncles, but in this group of plants (sometimes called the peduncular-spined euphorbias), the modifications to the flower stalks have been more drastic. A few of these euphorbias have stems divided into distinct tubercles, and are sometimes called corn-cob euphorbias, but other than that, the differences from species to species mainly lie in size of stems, and specific development of peduncular spines as well as differences in flowering parts. The corn-cob plants include E. fimbriata, E. nesemannii, and by far the most commonly cultivated, E. mammillaris. An intensely variegated, yellowish-white form of E. mammillaris is even more common in cultivation than the standard green form, although variegated plants tend to be very rare in the wild. Primary stems of these plants can reach a bit more than a foot in height, and the secondary branches that come from their base will gradually form a loose hemisphere. Other, non-tuberculate species such as E. enopla, E. atrispina, E. aggregata, and in particular, E. pulvinata, form masses of hundreds of densely packed branches up to six feet across, like a single huge cushion of stems. E. ferox also grows into dense masses, but its particularly stiff, thick and sharp spines set it apart—even though they’re really just modified dried flower stalks, they’ll rip your skin off as efficiently as a clump of cacti. Other species with similar stems are less densely packed and much taller, E. pentagona and E. heptagona reaching as much as five or six feet in height, while the many forms of E. horrida and the closely related E. polygona resemble barrel cacti, with thick stems up to two feet tall, making very cactus-like clusters (compare E. horrida and the Chilean Copiapoa cactus in the Arid House for striking examples of convergent evolution). Finally, the spines of E. pillansii are forked at their tips, while those of the barrel cactus-like E. stellaespina (also sometimes spelled stellispina) fork into multiple points, like sharp little stars, at their tips.
Though quite slow growing, E. stellaespina is a very tough plant that will gradually form spectacular clumps a couple of yards across. I’ve seen it growing on stony hillsides at high noon with ice still on the ground in the Western Cape Province. It will survive outdoors in our area, too, if given good drainage, but it’s always been fairly rare in cultivation. Many of the others in its group will also do well outdoors, and we have several large clumps of E. horrida on African Hill that have survived cold spells into the mid-teens without any damage. The peduncular-spined euphorbias are among the mainstays of outdoor succulent gardens, but will also do quite well in containers. The smaller species, such as E. atrispina, are perhaps better suited for indoor culture, but if you have the space, any of them will do fine.
The peduncular spined euphorbias, along with the finger-flowered species, will do best in extremely bright light; the others mentioned here can take less, and may need some protection from the brightest sunlight, or if in a southern or western facing window. All these euphorbias enjoy a standard succulent soil mix, with perhaps a bit more drainage for E. obesa and its relatives. Similarly, watering those very succulent species should perhaps be done a little more carefully, water perhaps every ten days or so during the warm months, every six weeks or so during their winter rest. The peduncular spined and finger-flowered plants, along with species such as E. susannae, can have water once a week when they’re growing in summer, about once a month in winter when they rest. The ones that will grow outdoors will adapt to our rainy and dry seasons, but some extra water in summer will help—I often leave outdoor plants dry from early October until the rains begin, providing them with the dry rest that most cacti and succulents seem to need.
The Garden has a good, if not comprehensive, collection of these plants, and perhaps we can experiment in time with a few more species on African Hill, as many will only come into their own if given the light and space of the outdoors. We often have some of these various euphorbias for sale as well.
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