| Snakes and Stars--Monadenium
Though they lack the diversity of species, the breadth of distribution, and the popularity in cultivation of their cousin genus, Euphorbia, the several dozen species of Monadenium have attractions of their own for anyone who enjoys succulent plants. Restricted to Africa, monadeniums occupy an approximately "J" shaped arc of territory that starts in Somalia and Ethiopia, sweeps through Kenya and Tanzania (their center of distribution), and reaches as far south as northern South Africa before turning west through Botswana and Angola. Most of their habitat, though dry, is tropical in temperature, lacking the extremes of cold and utter aridity that mark the domains of some of the most specialized forms of succulent plants.
The key difference between Monadenium and Euphorbia lies in their respective inflorescences, with the simple, euphorbia-like flowers of Monadenium partly hiding from view in a sort of cupping hood made of bracts and called an involucre. Some monadeniums have multiple involucres and in some the hoods flare out dramatically or become brilliantly colored, red or pink, but not many people would grow the plants solely because of their inflorescences. Instead, it's the range of odd shape and growth forms that monadeniums exhibit that provide their appeal.
To a certain degree monadeniums can duplicate the tremendous range of forms attained by the succulent euphorbias. In their most basic form, found in the small growing Monadenium invenustum, or the taller M. arborescens, monadeniums consist of one or more somewhat succulent stems (about pencil-thick in the smaller plants), with slightly succulent leaves that grow out of barely raised, sometimes spiraling, stem divisions. These stems and their usually deciduous leaves arise from a large, tuberous root. Regardless of their low level of overall morphological modification, these species have the complete array of flower-with-involucre that defines the genus.
The various groups of more specialized monadeniums have elaborated on these basic themes of succulent stems, tuberous roots, and, in the most typical species, stems organized into patterns of raised tubercles. These most typical plants (largely Kenyan and Tanzanian) make up a series of species in which the stems steadily become thicker and more succulent and the markings become more identifiable as increasingly prominent tubercles. Monadenium rhizophorum, for example, still has relatively thin stems, divided but not entirely covered by elliptical, spineless tubercules, while in M. lugardae the stems have thickened to an inch across, grow largely upright and are arranged into patterns of diamond shaped tubercules. In Monadenium heteropodum and M. guentheri the tubercles stand out boldly and come armed with small spines at their apices. Monadenium ritchie has dome-shaped rather than pointed tubercules and in M. schubei the tubercules are so pointed that the plant seems to bristle with spines, even though the actual spines at the tubercule tips are small and harmless.
When mature these monadeniums grow into dense clusters of sinuously bending stems that emerge from a tuberous base, like a colony of twisting, light-green snakes. Their persistent obovate or spatulate leaves and almost tubular involucres grow from the tips of the branches. In contrast, the rare, slow-growing Monadenium reflexum, from Ethiopia, has lost the dense branching habit and the tuberous base, as well as the persistent leaves. Its very long, reflexed tubercles point downward and give it a shaggy-looking appearance, and its foot tall, three inch wide main stem may have a couple of upward pointing branches, the whole effect of a mature plant somehow resembling a humanoid cartoon creature.
Instead of dense, precisely patterned tubercles covering their stems, a second group of monadeniums has developed stems scattered with prominent leaf bases ending in a cluster of small spines shaped like a star or sunburst. Monadenium stellatum, a rare species from Somalia with a longitudinally grooved wooden stem, has spiked leaf bases four times longer than thick, while in M. magnifica and its thicker-stemmed near relation M. spectabile, the leaf bases are lower, the starburst spines not as obvious, but the succulent, long-lasting apical leaves themselves come armed with decorative spines along their keeled midribs.
In other monadeniums the stems have become reduced, even deciduous, and the tuberous base has taken on more importance. These geophytic plants, with only underground parts much of the year, include species such as Monadenium majus, from dry parts of Ethiopia, and several species from unlikely habitats such as Angola, areas sharply divided seasonally between wet and dry. Some of these largely underground monadeniums have dramatically flaring involucres, with unusual patterns and markings.
In still another variation, Monadenium ellenbeckii, from Ethiopia and Somalia, consists of a cluster of small, succulent stems that emerge from a central base, but instead of spines or tubercles its branches are covered with a velvety, kelly-green epidermis that looks like corduroy.
On the whole monadeniums adapt to cultivation without much difficulty. Many won't ever outgrow a five or six inch pot, and they respond to bright light and warm temperatures. Generally, any quick-draining succulent soil mix will suit them, and the snake-branched or star-spined ones will do well with water about once a week in the warmer months, and every three weeks or so in winter (when they should be protected from cold). The dwarf plants with tuberous roots, especially the geophytic species, need to be kept drier in winter, and whenever they're not growing actively, although raising the tuberous base above the soil line will ease the danger of rot. The more "primitive" species are easy to grow in spite of their tuberous roots, and they can be watered a little more frequently in winter, or given a little less light than the others without much worry.
Nothing else really looks much like a Monadenium, and in recent years they have both become more available and more popular among succulent growers. The Garden has a good collection of Monadenium, and we propagate a few extra ones for sale from time to time.
|
