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For thisl installment on the genus Euphorbia, we turn to the enormous island of Madagascar , famous for its population of endemic mammals and notorious as a prime example of environmental destruction and habitat loss. The flora of Madagascar is as distinct as its fauna, with a major component consisting of a large population of succulent plants. One of these, the family Didiereaceae, grows nowhere but Madagascar , and many of the Madagascan euphorbias are sufficiently distinctive as to be almost immediately recognizable as well.
The extensive arid regions of the island, particularly in its southwest, are covered with large pachycauls from several genera of Didiereaceae, interspersed with pachypodiums and succulent, tree -sized euphorbias. These euphorbias resemble the very first ones discussed in this series, with succulent stems and branches, but without extreme morphological modifications. One well-known species, E. stenoclada, has branch tips hardened into sharp points, similar to the sharp stem tips of South African species such as E. lignosa, but these pointed branches have nothing in common with either the peduncular or stipular spines found in the true spiny euphorbias. These Madagascan euphorbias may have a succulent ancestor in common with similar South African species, or they may have evolved separately from non-succulent euphorbias as a response to climate and environmental change.
The actual spiny euphorbias of Madagascar form a very distinct group, unlike other euphorbia sections. Their stipular spines may well have evolved independently from the mainland African species, and their own sub-generic designation within the genus acknowledges their separateness.
Often called the “Crown of Thorns,” Euphorbia milii, by far the best known Madagascan euphorbia, is grown throughout the world. A typical plant consists of a spiny, densely branched bush, with paired spines, woody, not particularly succulent stems covered with thin green leaves, and typical, nondescript euphorbia blossoms distributed near its branch tips, surrounded by a pair of bright red bracts (also called cyathophylls). Besides this typical form, E. milii also appears in a number of forms and varieties, such as var. breoni, with much thicker woody stems and a larger, showier inflorescence. Variety imperatae, on the other hand, is a miniature version of a standard E. milii that can remain content and flowering in a three inch pot for decades. Other varieties of E. milii, less frequently encountered in cultivation, may bear yellow or even white cyathophylls. As a popular horticultural plant, the Crown of Thorns has probably been over described, with many minor variations granted possibly unwarranted official taxonomic recognition. Additionally, over the last several years many E. milii hybrids have entered the market, generally with much larger cyathophylls in various shades of pink, orange and yellow.
Other similar species differing primarily in bract color, arrangement and number include E. duranii and the very slow-growing E. horombense. When mature, many of these species form hemispherical mounds up to a yard across, an appearance not likely to be encountered with container grown plants. Slightly farther afield from the E. millii model, species such as E. croizatii and E. delphinensis have rounder leaves and less gaudy bracts. As more of Madagascar comes under botanical scrutiny, localized, small euphorbias keep being discovered. These include rarities such as E. guillemetii, with small, pinkish bracts, and the fairly recently discovered E. hoffstatteri, with variably colored bracts, a tuberous root, thick, spiny stems, and, in some forms, hairy leaves. Several species bear narrowly linear leaves, among them E. rossi, with beige bracts, and the pale green-flowered E. genoudiana. Still somewhat rare in cultivation, another linear-leafed species, E. gottlebei, differs from the others in its large, bright red bracts, very similar to E. milii itself. Among the species farther removed from the E. milii theme, E. didiereoides grows much like an ocotillo, with a spray of ascending, arching branches up to seven or eight feet tall, each equipped with distinctive short secondary branches, and tubular cyathophylls that enclose its flowers. Also with enclosed flowers, borne on long, sometimes pendent inflorescences, both E. perrieri and E. paullianii appreciate more water and a little less light than most of the others in this group. The related E. pedilanthoides, with flowers almost totally enclosed by swollen-based, tightly tubular, scarlet bracts, forms a compact plant with a distinctly thickened base, like a miniature pachycaul tree. Linear-leafed E. kondoi, another recent discovery, is a delicate grower which produces a large tuberous root.
Perhaps the most interesting of all these spiny species is E. guillauminiana, confined to a few arid lava beds. This species regularly rebranches, with the new branches all of an equal length, ultimately forming a nearly perfect hemisphere up to two feet in diameter and height. Cultivated plants slowly attain this shape, but collected plants already have it, and command high prices. One wonders about the viability of the species’ survival in the wild—although conditions in Madagascar are so precarious that leaving the plants alone might not offer much protection either.
Most of the plants that I’m lumping together with E. milii grow easily in cultivation. With a few exceptions, they like very bright light, and most do best with a somewhat richer soil than most succulents, water once a week (or even a bit more frequently) in warm weather, and water about every two weeks in winter. E. milii itself is marginally outdoor hardy in our area, but most of the others are both slow growing and somewhat rare, not good subjects for experiments in frost-hardiness. A few of these species require more care. E didiereoides should be kept somewhat drier during the winter, as should E. pedilanthoides and similar tuberous rooted species such as E. kondoi. In my experience E. rossii will suffer and possibly rot if watered too frequently in winter, and E. guillauminiana in particular requires very dry treatment after it drops its leaves; leaving it completely dry for a few months until it makes its new growth won’t hurt it, although water every six weeks or so is probably all right also. These water-sensitive species will also benefit from a leaner, quicker draining soil mix as well.
Another group of related Madagascan euphorbias grows in higher rainfall regions than most succulents. Their flowers are small, tightly enclosed by tubular, overlapping, often vividly colored bracts. These plants may slowly branch or may remain solitary, growing into small, often spiraling columns. They all produce large, rather tropical looking, though deciduous, foliage. Some, such as the various varieties of E. viguieri, are fiercely armed with thick based, sometimes jagged, often strikingly white spines that contrast with their bright green stems. Euphorbia pachypodiodes, with a spiny, purple-green cylindrical body topped by a rosette of bright green leaves purple-red underneath, and with an erect inflorescence of a few dozen tightly arrayed little flowers that look almost like some sort of vegetable radar tower, was almost unobtainable for years until a well-known grower wandered out to his greenhouse while drunk one night and somehow managed to successfully pollinate some plants. The species still isn’t common in cultivation. Others in the group have spines reduced to fringes running down their stems, and one of these, E. leuconeura, is both self-fertile and extremely prolific. Its flowers lack attractive bracts, but when young its leaves are marked with bright white veins. This plant, from areas of high rainfall in eastern Madagascar, may even grow epiphytically in tropical forests. It’s sometimes sold as E. lophogona, a less common (although certainly not rare) species with fringe “spines” that are more fibrous than in E. leuconeura, brown, woody stems, dark green, leathery leaves, and flowers surrounded by white or occasionally pink bracts. E. neohumbertii has a stocky green trunk marked with spiral patterns of white leaf scars and bristly spines much like E. lophogona. Its enclosing floral bracts are bright red; in the almost identical (but more freely branching) E. aureo-viridiflora, the bracts are yellow-green. Most cultivated plants of this group are small, but with time and root-room they may reach three feet or more in height. Though when leafless and dormant they seem more cactus-like than most Madagascan euphorbias, they take much the same care as the E.milii group; a fairly rich soil, bright light, and water once a week while in leaf and every two weeks or so after the leaves drop in late fall or winter.
A few odd species of Madagascan euphorbias remain mostly underground and produce annual rosettes of leaves. They show their relationship with the other Madagascan euphorbias when they flower, with their blossoms surrounded by decorative cyathophylls. The best known of these geophytic (underground stemmed) species is E. primulaefolia, with bright white bracts surrounding its flowers, which begin to bloom a little before its new leaves appear. In the wild this species and similar relatives, such as E. quartziticola and the very rare E. subapoda, look like uninteresting leafy rosettes accompanied by small, rather pretty flowers. In cultivation, however, it’s best to raise their tuberous bodies above soil level, both for display and to prevent them from rotting; thus the little rosettes suddenly are transformed into fascinating caudiciforms. A few other described species share this habit, and as the plants are almost invisible much of the time (completely so when out of leaf), there may well be others yet undiscovered. As with most tuberous-bodied plants, fast draining soil and a bit of care when watering is best, but given proper treatment, these little euphorbias will do well for many decades.
Still another group of Madagascan euphorbias consists of spineless plants that when dormant look like smooth-stemmed, generally solitary columns. Many of these flower before they leaf out, with inflorescences that cover the top of the stem like a decorative hat. The best known of these may be E. ankarensis; others include E.millotii, with thinner, sometime branching stems and veined leaves, E. moratii and E. albertii. Still uncommon in cultivation, they need a little less light than most of the species mentioned so far. They enjoy a good deal of water when growing, but should be kept quite dry after their leaves fall.
A final group consists of typically low-growing species with somewhat succulent leaves. These plants crawl along the sandy dirt and undergrowth of their home, sometimes, as with E. cylindrifolia, sending out underground shoots and rhizomes. A plant with small, terete, almost black leaves and apricot-colored bracts surrounding its flowers, E. cylindrifolia forms a mass of underground stems, even sending new branches out through the drain holes at the bottom of a pot. Its subspecies tuberifera, less robust and quite slow-growing, forms a caudex rather than rhizomes. Several in this group have very decorative leaves, highly crisped and zigzagged along their margins, among them the low growing, freely branching E. decaryi, the slightly more erect E. capsaintemariensis, the tiny, extremely slow-growing E. tulearensis, and two rare caudex formers, E. ambovombensis and the recently discovered E. suzannae-marnerianae. The leaves of E. francoisii range from rhomboidal to nearly linear in shape, in color from plain green, to green with pink, to pink and silver, to almost pure silver veined with pink and green lines, to random splotches of silver, pink and brown. The explosion of new species of these groups of Madagascan euphorbias results from a combination of extreme endemism and a very low profile; in time, some of these new species may be sunk and combined with others. In any case, there is a world of unusual forms, shapes and colors in these many miniatures from the giant island.
Most of these succulent-leafed species do best with good light, average (once a week) water in the growing season, and water every three weeks or so in winter. They like a quick draining soil with some organic matter in it. On the whole, these miniature euphorbias grow easily, and many will never outgrow a three inch pot.
In fact, most Madagascan euphorbias are reasonably easy to grow—I’ve noted some of the exceptions. Most will root from stem cuttings, although this is problematic and perhaps impossible in the case of the geophytes, and though the species with tuberous bases will root from cuttings, it’s not clear if these cuttings will ever produce tubers. Since they don’t need too much light and many remain small, some of these plants make ideal window-sill growers. The bigger ones, though needing protection from cold, make a distinct addition to any succulent collection.
Finally, a clarification to my cultivation hints from last month. As I said, both the caudiciform twin-spined types, such as E. tortirama, and the medusa types will root from stem cuttings, but generally the cuttings just elongate instead of developing into a typical plant. In addition to chopping them off and then rooting the multi-stemmed offsets that may develop from the cut, given time the snake-like branch propagations (particularly of the medusa types) often produce multi-stemmed secondary heads on their own, and these can be detached, dried off and rooted, and will grow into normal adult plants. It’s possible, though not as reliable, to do this with the caudiciforms as well (with a bit of luck), and E. knuthii, which is a sort of caudiciform, will make perfectly normal plants from a stem cutting without additional effort. As always, when cutting euphorbias, be careful about the sap, wash your hands religiously after working with them, and avoid contact with your eyes, nose or mouth. Euphorbias sap varies greatly in toxicity, and people differ in their sensitivities as well, but caution never hurt, while carelessness can. Enough preaching, now why not try growing some?
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