| Some Other Pachycauls: Elephants and Kapok
As noted last month, the term “pachycaul,” along with the associated term “caudiciform,” doesn’t refer to a group of related plants, but instead to plants with similar morphological development. Plants from a number of families have adopted this form of growth. For example, there are pachycauls in the Euphorbiaceae, along with its myriad of more typically succulent species, and there are odd, isolated species from quite unlikely families, such as Papaveraceae, the poppy family, that have evolved into pachycauls as well. Even though pachycaulous plants come from rather arid habitats, they generally experience fairly good rain during their growing seasons, when they put out their thin, quickly deciduous, green leaves. In this column we’ll focus on several genera from two families that contain some of the most interesting, popular, and certainly the largest, pachycauls.
A widely dispersed family that includes several fantastic pachycauls among its members, the Anacardiaceae also includes both useful and decidedly unpleasant non-succulent species. Both cashew nut trees and poison oak belong to this family, but neither has had to adapt to arid situations. In contrast, the single species of Pachycormus, P. discolor, manages to thrive in the dry heat of Baja California, where it may reach eight or ten feet in height and a couple of feet in diameter in deep soil, or remain short, with a fantastically thickened trunk, in rocky or windswept areas. Pachycormus grow along with burseras, Burseramicrophylla in particular, and though both are called elephant trees, Pachycormus discolor, with their always greatly thickened trunks, seem more deserving of the name. Bursera have a wider distribution than Pachycormus, whose habitat pretty much consists of the center of the Baja bursera range. Sometimes growing almost literally next to each other, with a similar general appearance and superficially similar pinnate leaves composed of very small leaflets, the easiest way to tell the two plants apart is the scent, or lack thereof, that emanates from their foliage. Whether crushed or just dented, Bursera foliage will immediately perfume the surrounding air, while the leaflets of Pachycormus are essentially odor free. When flowering, Pachycormus produce dense sprays of small blossoms, again, quite distinct from burseras. The average Pachycormus is extremely succulent, with its pale, peeling-barked trunk greatly outsized in proportion to its limbs, while in many places burseras look more like shrubs, their succulent main stems somewhat hidden by their dense branches. Oddly enough, however, though pachycormus were growing along with the exceptionally modified Bursera microphylla I mentioned last month, they weren’t as highly changed from their typical habit, and in those circumstances seemed less extremely succulent than their unrelated neighbors. In other regions of the arid Pacific coast of Baja, however, extremely succulent forms of Pachycormusdiscolor have been reported, called “jug-type” plants because of their extremely broad, short, almost circular trunk, similar to the windswept burseras, or some of the Madagascan pachypodiums, such as Pachypodiumrosulatum or P. decaryi.
Also from the giant island of Madagascar, half a world away from Baja California, the Madagascan genus Operculicarya shares both the succulent life style and the tiny, highly pinnate leaves of the elephant tree; though never forming the extreme “jug” type of growth. Unlike pachypodium, it actually is a close relative of pachycormus and a fellow member of the Anacardiaceae. With only a few species, operculicarya remains somewhat rare in cultivation, although O. decaryi has become reasonably widely available over the last several years. O. decaryi forms an odd, pachycaulous trunk, heavily wrinkled in more-or-less vertical strips and shaped almost like an elongated cone that suddenly tapers at its top. Its thin, relatively scanty branches often grow out at almost a horizontal angle, accentuating the thickness and general weirdness of the plants. In cultivation O. decaryi maintains its leaves for most of the year, and though its thickened, oddly furrowed and ridged main trunk develops relatively slowly, a seed grown plant will develop its adult form more quickly than either pachycormus or bursera. The other operculicarya species are much more rare, almost unknown in cultivation, and most of them are somewhat larger, sometimes multi-stemmed plants with less extreme pachycaulous development, although they would all be interesting subjects for cultivation if they could be found. An exception is O. pachypus, quite similar to O. decaryi, with it irregularly tapering conical trunk up to about five feet tall and close to two feet broad at its base. I wouldn’t be surprised if some growers somewhere have been able to obtain seed, and this is a species to look for.
Bombacaceae, the bombax family, the home of the largest succulent plants of all, has a widely dispersed range over much of the warmer parts of both the Old and New Worlds. Many of its genera consist of trees with somewhat swollen bases and disproportionately swollen trunks. Chorisia, from South America (and used widely in southern California as a landscape tree), embodies the look; a medium-sized tree, relatively sparsely branched, with compound leaves, a thick trunk covered with pyramidal spines, and a spectacular display of large, pink flowers followed by large, pendulous fruit. The huge trees of Ceiba, from Mexico through Central and South America, looking as if they were made of smooth, gray cement, and with thick, buttressed trunks and enormously swollen bases, come a little closer to being true succulents, but, perhaps because of their need for tropical climates, or their enormous mature size (well over 150 feet tall), they’re not grown by succulent collectors. As with other members of the family, the seeds that fill their pendent fruit are attached to fluffy appendages, the original source of kapok.
A third genus, in reality almost as impractical for cultivation as Ceiba, nonetheless has attracted the attention of succulent growers. This, of course, is Adansonia, the baobab tree. Baobabs grow over most of the drier parts of Africa, Madagascar, and one species (A. gibbosa) occurs in Australia. Most people have at least some idea of what a baobab looks like, an enormously thick trunk, growing upright and abruptly dividing into several thickened main limbs, which then subdivide into more ordinary branches and twigs. A. digitata, the single continental African species, is best known, with a trunk over sixty feet tall and sometimes thirty feet thick, filled with soft, spongy wood, but some of the seven species from Madagascar are the most fantastic. There is (at least for the moment…) a famous road of huge A. grandidieri that rivals any of our avenues of redwoods, and beats them hands down for general surreal effect, and Adansoniaza, a lesser known species, has some of the most fantastic trees imaginable among its members. People like to raise adansonias, but unless you can allow them to grow up to twenty or thirty feet tall (and remember, they can’t take cold), they’ll remain permanently spindly seedlings.
The member of the bombax family most suitable for cultivation is, conveniently, bombax itself. Bombax, a small genus of Mexican trees, can become large—B. ellipticum, the most common in cultivation may reach 100 feet in height—but in rocky situations and in drier climates, the plants look utterly different. They thicken and remain short and stunted, with secondary branches reaching a couple of yards into the air at most, their trunks over a foot across, sometimes hugging the ground and shaped like a small boulder, or curving around and wedging into actual boulders. In cultivation, these fantastic shapes can’t really be achieved, but the plants will remain happy for decades in six or eight inch pots, developing a thick, fairly symmetrically flaring base and thickened main branches in a satisfying manner. B. palmeri, from northwest Mexico, never gets as large as its more widespread cousin, and will perform at least as well in cultivation.
Once obtained, the succulent Anacardiaceae do well in cultivation. Pachycormus, from the winter rainfall areas of Baja California, should be watered when it starts its growth in fall, and dried off as its leaves fall in April or May. When dormant, water every three or four weeks won’t hurt it. Pachycormus grows in the driest environment of any of the plants under discussion, and a fairly lean, somewhat rocky soil mix and the brightest possible light will suit it well. A few degrees of frost won’t hurt, but our over-abundant winter rainfall would probably prove fatal fairly quickly. Operculicarya grows in the warmer months, and can take a somewhat richer soil mix than pachycormus. Water once a week in summer, and some water every three weeks or so in winter will help the plants thrive in a bright, fairly warm place. Operculicarya was very rare in cultivation ten or fifteen years ago, but now quite a few succulent nurseries offer them, and Pachycormus (considerably slower growing) is also offered from time to time.
Most of the succulent Bombacaceae, as mentioned, simply get too big to make satisfactory cultivated specimens, though people are always trying various species of Adansonia. Although they ultimately turn into what can legitimately be called the world’s largest succulents, baobabs do well with a surprisingly large amount of water. In the warmer months they shouldn’t dry out, with water twice a week or even more a good idea, and in winter they don’t appreciate long droughts either. In contrast, Bombax does well with typical pachycaul care; regular water when the new leaves start, reduced water (about every three weeks) after they fall, very bright light and a fast draining soil mix. Seedlings of B. ellipticum appear from time to time, and though B. palmeri is less common, with effort you may be able to find one.
Though ultimately perhaps a bit impractical, the smaller growing succulent Bombacaceae make fine container plants for many years, while the succulent Anacardiaceae are among the very best of the miniature tree type succulents, the natural bonsais so sought after by growers and collectors. With skill and a good deal of patience, cultivated plants of some of these can be raised to rival the best natural forms.
The Garden has some very nice specimens of Pachycormus, a small Operculicarya decaryi, and a number of different members of the Bombacaceae. From time to time we have seedlings from these groups available at sales.
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