Succulent of the Month


Melons and Turk's Caps

By a curious twist of fate, the first cactus ever seen by Europeans was a member of one of the most peculiar and in many ways anomalous genus of the family. Brought from the West Indies back to Spain by Christopher Columbus, this Melocactus (for that’s what it was) caused something of a sensation, as no one in the Old World had ever seen a plant even remotely like it. It’s hard to say definitively what early fifteenth century courtiers would have thought about such a thing. Would they have wondered about the plant’s long spines, organized in symmetrical clusters, or perhaps the remarkable, thickened body, similar in way to the fleshy root of a beet or turnip, but obviously designed for life above ground? We can guess, however, about the most memorable part of the strange new plant, its cephalium, for it led to its popular name, the “turk’s cap,” and interestingly enough, only Melocactus, and the ecologically similar genus Discocactus possesses this type of permanent, apical, hatlike appendage. The other nickname, “melon cactus” (or simply “melon”) presumably refers to the shape (like an apple—Malus) of a precephalium-sized plant.

It’s only when a Melocactus reaches maturity that the cephalium begins to grow. Cylindrical, with a diameter distinctly smaller than that of the plant body proper, the cephalium will keep growing for the rest of the plant’s life, but the body of the plant stops growing the moment the cephalium starts to form. At a certain stage the cephalium somewhat resembles a fez sitting on top of a larger head, and thus the nickname. Adding to the resemblance, the cephaliums of most species of Melocactus have a covering of orange or red bristles. As the plants age the cephalium doesn’t increase in girth it will steadily grow taller, in some species reaching over two feet in height, out of the body of a globular cactus no more than a foot or so tall. The cephalium bears small flowers and fruit that sometimes remain embedded inside, with seeds waiting, perhaps, for the parent plant to die and provide a bit of organic matter for them to germinate in their surprisingly inhospitable environments.

Melocacti generally live in areas we don’t associate with cacti; the islands of the West Indies, the east coasts of central and northern South America, places with lots of heat and humidity. The sites chosen by the plants as habitat, however, offer little in the way of tropical splendor. A typical Melocactus site looks something like a parking lot made of huge flat slabs of stones instead of asphalt, with a few narrow cracks running here and there. These cracks serve as homes for the plants, and there often will be fairly good-sized plants, over a foot tall and wide, growing out of a crack perhaps an inch across. Many of these sites are close to the sea as well, with the salt air drying things out even more. Only in a few places in Peru do melocacti occur at some altitude, growing at as much as 6500 or 7000 feet, but there too they will typically just sit in tiny fissures in otherwise quite barren expanses of solid rock.

An immature melocactus simply looks like a smallish barrel cactus, and there is nothing in its appearance that would suggest anything odd about its cultural needs or ecological propensities. These will become only too obvious, however, if the plant is subjected to any degree of cold, with severe damage or death occurring at temperatures that the great majority of cacti wouldn’t mind in the least. A few Peruvian and other Andean species (as well as occasional Brazilian plants) can survive a typical Bay Area winter without heat if kept dry, but keeping them warm won’t hurt them either. The root systems of melocacti are notoriously weak and difficult to reestablish, a consequence, presumably, of their preferred habitat of next to no soil. Nonetheless, again as a result of their tropical origins, they need a fair amount of water, and most prefer more frequent water in winter than other cacti, say once a month. Their soil mix should be very quick draining, and they like very bright light, not as much as the most arid growing cacti, but plenty nonetheless.

Most melocacti look pretty much alike, ribbed globular plant with outward facing spine clusters distributed along the edges of the ribs. Some species (such as the aptly named Melocactus longispinus—sometimes considered just a form of M. ernestii) have very long spines, but all species are well armed. Other species that are sometimes encountered in cultivation include Melocactus bellavistensis (from Peru) and M. broadwayi and M. intortus, both from the West Indies. In contrast to the typical cephaliums covered with reddish bristles, in some melocacti, such as the very rare Brazilian Melocactus deinacanthus, the upper portion of the cephalium tends to remain white, with few bristles to poke out beyond a layer of woolly fibers. A few species have pure white, bristle free cephaliums, and one of these, Melocactus glaucescens, combines a cephalium densely covered in curly white wool with an almost sky-blue body. A last species, Melocactus matanzanus (from Cuba), resembles the more typical species, with a bristly orange-red top, except it rarely reaches more than four inches in diameter, and grows to maturity relatively quickly.

In many ways similar to Melocactus, the genus Discocactus grows only in Brazil and a few parts of Bolivia and Paraguay not far from the Brazilian border. Discocactus consists of round, often somewhat flattened little cacti, rarely more than six inches in diameter and often less than half that size. Their bodies look like a small melocactus but in contrast to that genus, discocacti bear much less fierce spines that adhere closely to the body of the plant, and in the case of the tiny Discocactus horstii, are little more than harmless tufts. Discocactus cephaliums arise from the apex of the plant, but don’t get very tall and lack the reddish color or glassy texture of Melocactus cephaliums. Their proportionately much larger flowers are white and seem more suited to a columnar cactus than to a squat tiny little plant. The plant sometimes called Discocactus araneispinus (also considered just a form of D. zehntneri) clumps from the base fairly readily, and as a result shows up in the trade fairly frequently; the other species stay solitary and mostly have remained rare collector’s items.

These cacti are not the easiest things to grow. They generally resent being repotted and can take a long time to establish. Most of them can’t stand cold, or even fairly cool temperatures, and though they can’t endure long stretches of total dryness, too much water will rot them, as their weak root systems tend to be inefficient at sucking up water from wet soil. Melocactus glaucescens, M. matazanus and Discocactus araneispinus may be the easiest examples to grow, but even they aren’t plants for beginners. When grown to maturity, however, both Melocactus and Discocactus possess an exotic look shared by no other cacti, and they’ll generally attract a lot of attention.

The Garden has a very good collection of Melocactus (20 species out of 31 known). We have a few small ones for sale from time to time.

-Fred Dortort

Fred Dortort has grown cacti and succulent plants for thirty years. He's studied and observed plants in Baja California, mainland Mexico, South Africa, Namibia and the American southwest. He's lectured widely on succulent plants, has taught classes at the Botanical Garden, and written numerous articles for the Cactus and Succulent Journal, as well as publications such as Pacific Horticulture and Garden.

Fred is a Garden Volunteer. We appreciate his time and knowledge, working with the succulent and cactus collection (Arid House) and helping with propagation for our Plant Sales.

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