The Spitzkoppe, a dramatic mountain range in central Namibia.

In May 2018 I made my first trip to the African nation of Namibia. Located on southern Africa’s western coast, north of South Africa, south of Angola, and west of Botswana, Namibia is a vast, arid landscape with a tiny population of only 2.65 million people (2019 estimate) spread out over an area nearly as large as the states of Texas and Oklahoma combined. Oklahoma alone has almost 4 million people, and while that state may be somewhat known for expansive landscapes, Namibia has fewer people and a much larger area, which gives some indication of how sparsely populated this large country is.

The Spitzkoppe mountains are comprised of 120 million year old granite, uplifted and exposed by erosion into what are called “inselbergs”, or “island mountains”.

Spitzkoppe means “Pointed Dome” in German, which alludes to the Namibia’s recent colonial history since a number of place names in the nation originate in that language. German colonial rule began in 1884 under the name of German South West Africa, and was ended in 1918 under the Treaty of Versailles at the end of World War I, in which Germany was defeated. The former colonial territory then became known as simply South West Africa, and was administered politically by South Africa until 1990. This brief history of course skips over decades of conflict between South African troops and Namibian independence movements, who demanded that the country be renamed Namibia in 1968, and who achieved final independence from South African colonial rule in 1990.

The Spitzkoppe Mountains are home to works of rock art and ancient archaeological history of native Namibian tribes who have lived here for many thousands of years.

Also missing from the discussion is a detailed report of the several native peoples who have called Namibia home for tens of thousands of years, including the Herero, the Namaqua, and the Damara tribes, among other smaller groups elsewhere in the country. The name “Namibia” is derived from the Nama language, and refers to the Namib Desert, meaning “vast place”. The Nama and Damara tongues are part of a famous group of so-called “click” languages, which utilize some unique sounds not normally used in spoken language and are clicks, pops, and hisses that don’t use vocal chords or the larynx. Most of these tribes were hunter-gatherers or nomadic pastoralists depending upon livestock for their survival.

An example of Damara being spoken by our guide Susana, while we were visiting an area of petrified wood tree trunks amidst Welwitschia mirabilis plants earlier in the trip.

A hillside in the Spitzkoppe with sparse Namib Desert vegetation.

The Namib Desert is widely considered to be the oldest desert on earth, having existed more or less in the same place on the same continent for at least 200 million years. Africa has not experienced as much continental drift via plate tectonics as other landmasses such as the Americas, India, and Antarctica, and as such the Namib Desert has had a long history of evolution as a warm and arid land, uninterrupted by wetter periods or ice ages. Many desert organisms, both plants and animals as well as other phyla, have developed unique traits over this lengthy history, and many Namib Desert species exist nowhere else on earth.

Zooming in on the hilltop in the photo above, several interesting succulent plants become evident….

These two squat-shaped trees are cobas trees, Cyphostemma currorii.

One of Namibia’s most fascinating and distinctive plants is Cyphostemma currorii, the so-called cobas tree or butter tree. These bizarre vegetables are members of the grape family, Vitaceae, and are indeed related to other much better known plants such as grapevines (Vitis vinifera) and Virginia creeper (Parthenocissus quinquefolia). There are also other succulent grape family members in the genus Cissus which have trailing, clambering stems, but the Cyphostemmas are surely the weirdest of them all.

Another large succulent of the Spitzkoppe is the gifboom, or poison tree, Euphorbia virosa. The specific name of virosa refers to the extreme toxicity of the plant’s sap, which can cause burning rashes on the skin and blindness if it enters the eyes. Note the cobas tree up on the hill near the summit.

A view of a Spitzkoppe hillside studded with large granitic boulders and several succulent species, including large E. virosa and several types of Commiphora trees, as well as the Cyphostemma.

Cyphostemmas are unearthly, and nothing else really looks like them aside from some of their fellow African succulents found hundreds of miles away, plants loosely called desert roses (Adenium spp), which bear a passing resemblance but are botanically unrelated.

One can see why the plant might be called butter tree, for the smooth, waxy trunk. It’s interesting to observe how the trunk almost melts over the boulders surrounding its base.

The Namib Desert around the Spitzkoppe enters winter dormancy.

When we visited Namibia in the second half of May 2019, it was late autumn in the southern hemisphere, the equivalent of November in the northern hemisphere. Rain, when it does occur here, tends to fall mostly in a short late summer through early fall season which enables a brief period of growth and activity. Unfortunately, this region was experiencing a severe long-term drought lasting close to a decade. Many of the plants were showing signs of long-term drought stress, and some, such as quiver tree aloes (Aloe dichotoma) were already dead or approaching death.

A winter-dormant Cyphostemma currori.

The species is named for Andrew B. Curror, who first collected specimens of the tree at Elephant’s Bay in Angola in the 1840s. This species is found only in the countries of Namibia and Angola, and mainly in the Namib Desert, generally somewhat inland from the South Atlantic Ocean. The famous gigantic sand dunes of the Namibian “Skeleton Coast” do not support Cyphostemmas, which prefer to inhabit rocky terrain with summer rainfall as opposed to nearly rainless foggy desert dunes. They do well about 50 miles/80 km inland to the east, where they favor canyons, rocky escarpments, rugged mountain ranges, and nearby gravel plains.

Detail of the thick trunk of C. currori.

Clearly one of the most striking features of cobas trees are their massive water-retaining trunks, which are capable of getting them through years-long droughts if necessary. The trunks generally appear smooth, although there are zones with flaking or peeling papery sections present as well, although not as much as some nearby trees in the genus Commiphora which share their habitat.  Cobas trees might reach as much as 20 feet tall (~6 meters) but 12 feet (~4 meters) is a more typical size. Large and mature specimens might have trunks that reach well over a meter in diameter.

While the Spitzkoppe region can occasionally experience slight frosts of 28 F or so (-2 to -3 C) this is generally a nearly frost-free climate, and as such these trees do not have the relatively high cold resistance seen in saguaro cacti of North America’s Sonoran Desert, for example. This is one reason why they are seldom grown outdoors in the USA outside of coastal California, and even there they are nearly unknown. Most people have simply never heard of, or even conceived of, such a strange tree. Their slow growth rates and long development times don’t help make them more common either, it must be said.

There are several succulent species contained within the framing of this zoomed-in telephoto image. How many types can you identify? Answer below the next photo….

A large 10 foot tall Euphorbia virosa grows on a ridge overlooking a bald granite slip face in the Spitzkoppe Mountains.

(The answer to the photo quiz above is that there are at least four Cyphostemmas, two tree aloes, several Euphorbias, and at least two species of Commpihora, a succulent caudiciform tree, visible within the image.)

That poison tree euphorbia is at least 10 feet (3 meters) tall and wide with around 40 stems. Heeding the advice I have read about this plant, I did not even touch it lest my skin break out in a rash from simple surface contact. Some people react to it just like poison ivy, and I wasn’t about to find out my personal sensitivity level.

The Latin specific name of Euphorbia virosa is derived from the same root term as the words virus, viral, and virulent, and the epithet was applied for a definite reason. The sap of E. virosa was used for tipping poison arrows to kill game. It’s a very dangerously toxic plant, which you might need to become in order to not be consumed in such a harsh, arid region. If you have millions of years to evolve the biochemistry to defend yourself this vigorously, wouldn’t you do it too?

A quiver tree (Aloe dichotoma) manages to put forth a few flowers despite the ongoing drought.

Sadly, many of the tree aloes we saw on our journey through Namibia were either dead or dying due to long term persistent droughts across the country since about 2012. This may well be due to human-induced climate changes, which are predicted to affect semiarid regions more harshly than many other ecosystems by making them even drier than they already naturally are.

I do not know what this small woody tree clambering across the surface of a boulder in the Spitzkoppe is, but I appreciate its bonsai elegance.

The gorgeous trunk of one of several dozen southern African Commiphora trees. I don’t know any of them by species, although as a genus they are fairly distinctive.

Here is the peeling-barked trunk of a species of Commiphora. This is one of the three main semisucculent to succulent genera of the torchwood family (Burseraceae), with the primarily New World genus of Bursera and the mostly Afro-Arabian trees of the genus Boswellia being the other two. Known commonly as elephant trees or alternately as incense trees, most members of the Burseraceae have fragrant resinous sap often used as incense, in traditional medicines, and as essential oils. Both frankincense (Boswellia sacra) and myrrh (Commiphora myrrha) are in the family and are found in the Horn of Africa and the Arabian Peninsula. I do not know if the southern African species of Commiphora are used for resin production, but some of the North and South American Burseras are, producing a resin called copal.

Shot from a distance, I believe this is a thick-based tree called Sterculia africana.

And a second example, with very attractive reddish peeling bark.

Another interesting xeric tree with thickened trunks adapted towards water storage is Sterculia africana, sometimes called the “mopopaja tree”. The species is widespread across eastern and southern Africa, ranging from Somalia to Ethiopia and Sudan, down to Zambia and Mozambique, and west to Botswana and Namibia. It is also found across the Red Sea in Yemen on the Arabian Peninsula. As with most Namib Desert trees and shrubs, these are winter and dry-season deciduous, losing their leaves in May and June. Although clearly the first specimen shown still has a full leaf crown, while the other red-trunked specimen has lost almost all of its foliage.

I do not know what this prickly, defensive shrub is eking out a niche between large rocks. It has a Cyphostemma neighbor just across the outcrop, however!

I guess this could be a plant in the currant family, or sometimes nightshades adopt this kind of posture, or it could be an African family I know nothing about. Whatever it is, it’s cool and vicious.

We came across several of these Cape ground squirrels (Xerus inauris) standing sentinel on the flats at the base of the Spitzkoppe.

Cape ground squirrels (Xerus inauris) are named for the Cape Region of South Africa, which is actually a somewhat misleading name as they are not really found in what is usually considered the Cape Region of shrubby fynbos along the coastal zones. Instead, their range extends much farther north and they are primarily animals of the interior Kalahari and Namib Desert regions of central and northern South Africa, plus most of Botswana and Namibia. The common name was probably given more to distinguish them from eastern gray tree squirrels, which are introduced from Europe and are not native to southern Africa.

Despite the similar pose, this is a different individual. At a distance we mistook them for meerkats, which they do in fact often share burrow networks with.

Cape ground squirrels inhabit semiarid and arid zones in colonies ranging from 6 to 10 individuals. Colonies are gender-segregated, with groups containing either females and offspring of either sex, or males without offspring. The main time that the two sexes interact is during female estrus, which is mostly in late fall or winter although some breeding does occur year-round; otherwise females and males live separately in open-membership groups without a strict hierarchy, and whose size can fluctuate daily or weekly based upon who comes and goes.

For rodents, they are fairly large and can stand over 12″ (30 cm) tall not including the bushy tail, and weigh 1 to 1.5 lbs (about .5 – .75 kg). They are vigilant against potential predators and operate diurnally with foraging, breeding, and social behaviors. They do not hibernate or store food, so they are active every day year round. Food is mostly vegetable matter, ranging from seeds and bulbs to fruits and leaves, but some insects are also eaten. Males are evidently noted for their large testicles, which are golf ball-sized and very big for such a small creature. I think the individuals I photographed were females.  😉

As we completed our circumnavigation route around the Spitzkoppe, I spotted an unusually leafy plant growing on a rock outcrop some distance away from the dirt track we were on.

As suspected, it was a Cyphostemma that had not yet gone fully winter dormant, unlike the other plants that we saw earlier.

This cobas tree was not as large as the first specimen I approached, being perhaps about 7 feet/2 meters tall and with a trunk perhaps only slightly thicker than a foot/30 cm.

The leaves, when present, are thick, leathery, and have three leaflets. Each leaflet is easily mistaken for an entirely separate leaf due to their large size but they are in fact leaflets occurring in groups of three per petiole.

This cobas tree is showing signs of impending dormancy, as leaves curl, yellow, dry up, and drop off. Note how tightly the trunk is wedged in between the rocks as it grows in diameter.

Cyphostemma currori leaves emerge in the warm season, either slightly in advance of the annual summer rains or as they begin, and are retained for 4 to 5 months. Flowers emerge at the same time as the leaves, and fruits are borne in clusters much like their grapevine relatives.

Here are the fruit clusters of a related species, Cyphostemma juttae, photographed on August 31, 2012 at a cactus and succulent garden center in California. Very pretty, and very inedible to people.

All parts of the cobas tree are toxic and fruits, while red and juicy and appealing to birds and Cape Ground squirrels, are inedible to humans. This is due mostly to high levels of oxalic acid in all parts of the plant. While humans can eat plants containing very small amounts of oxalic acid without distress (like spinach or wood sorrel), larger quantities will cause severe gastrointestinal problems and kidney failure, so the rule for people is to not be tempted by the apparently palatable appearance of the fruits in a barren desert climate.

Detail of the thick, forked branches of the small and still-leafy cobas tree shown above.

As referenced before, the bark of Cyphostemmas is generally smooth but does peel off in thin flakes in some places. In this photo it is easier to observe the green cambium layer just below the yellowish-tan cortex. This permits some photosynthesis to occur even while the tree is leafless, which is most of the year, and helps it manufacture some food to stay alive while otherwise dormant and awaiting infrequent rains. Some drought years in the Namib Desert see very little rainfall, even by reduced desert standards, and it is important that plants here can avoid activating their metabolism when it is too dry to put out leaves. This is part of why so many of the arborescent plants have developed those thick, succulent trunks with thin, peeling bark that allows for a small amount of backup photosynthesis during the occasional even-worse-than-normal year of rainfall.

Dormancy phase: Activated.

When going dormant, plants of various types typically withdraw water, starches, sugars, and minerals from their leaves and translocate it for storage into other body parts, usually stems or roots. You see this with the foliage of familiar bulbs, with many herbaceous perennials and grasses, and with deciduous trees in cold winter climates as well. Foliage turns a different color, usually at least yellowish, and then withers and drops off. Rather than wasting the energy invested in leaf formation by losing all foliage quickly and while green, it makes much more sense to take as much of that back as possible before shedding occurs. This is why it’s important to allow your plants, whatever type they are, this period of “looking ratty and tired” before you cut off the foliage in the interests of tidiness. Don’t push them too far, too fast, or else you can easily compromise their dormant period survival.

A view of the Namibian Desert landscape. The Nama name meaning “vast place” is an entirely apt descriptor.

Being a succulent is not a necessary precondition for this withdrawal of water and various nutrients, but many succulent caudiciform trees operate this same way. It is in fact metabolically quite similar to the well-known modes by which deciduous broadleaf trees change colors and drop their leaves before the arrival of cold winter weather makes photosynthesis largely impossible anyway. Just because they only turn a dull yellow before they drop their leaves, and that it is induced more by dryness than by sheer frigidity, doesn’t mean this plant and others like the Commpihora and Sterculia trees nearby aren’t entering a fall/winter dormancy mode.

Another still-slightly-leafy juvenile cobas tree appears.

Walking on the way back to the rental truck, I discovered a third, even smaller Cyphostemma currorii mostly hidden in the thicket of a thorny shrub. As is common in deserts elsewhere, the so-called “nurse plant” phenomenon is an important ecological dynamic whereby seedlings of various plants, both succulents and non, require years or even decades of protection from the harshest of desert elements before they can survive in the open. Nurse plants provide this protection, mostly from heat, excessive sun, cold winter nights, and discovery and consumption by animals. Without the presence of already-established mature plants in a functioning ecological community, many species would either not survive their nascent stages of life at all, or do so only in very low numbers.

Nurse rocks can also serve this same type of protective function, as seen with the larger leafy cobas tree that I just highlighted. But since most of the desert lacks large rocks over most of its surface area, it is other plants that do the majority of the work of helping their neighbors to perpetuate themselves.

Self-portrait with a celebrity cobas tree, a species I had long wanted to see in habitat.

Cyphostemma currorii growing at Hosea Kutako International Airport in Windhoek, Namibia.

To finish off, I’ll include a selection of Cyphostemmas being grown in captivity. The one above is one of about 7 or 8 planted in front of the main airport in Windhoek, the Namibian capital city of about 350,000 people. I took photos of others as well, but in between the rush to return our rental truck and get into the terminal to fly back to Cape Town, the effort was a bit hasty and there’s plenty of visual clutter in each picture so they aren’t particularly worth highlighting….

I found this photo of what I think may be the same plant, just from the opposite angle, on Wikipedia’s page of the Windhoek airport so I will add it here for completeness. I like this photo better than mine anyway.

Here is a magnificent specimen with coppery tinted bark growing in the main conservatory near the entrance of Kirstenbosch National Botanical Garden in Cape Town, South Africa. The smaller Cyphostemmas growing to both sides underneath the big one are probably C. bainesii and/or C. juttae.

More detail on the leaves of the prior plant. Here it is easier to see the tripartite leaflets that comprise a single leaf of the cobas tree. These must be among the largest three-lobed leaves in botany, although I suspect there may be tropical legumes that also have a large size.

Another cobas tree growing at the Kirstenbosch entrance just a few feet from the first one.

And yet another in the Kirstenbosch conservatory, but more towards the middle of the glass house. They are all such unique individuals as they develop into mature specimens, each one different.

One more. This one has more flaking bark than the others, but the green photosynthetic cells of the trunk are clearer to see.

Cyphostemma bainesii, one of the other caudiciform species in the genus. This species is generally shorter than one meter tall at maturity. Leaves are smooth and waxy, and it also lives in Namibia.

Another incredibly cool and wonderful Namibian resident is Cyphostemma uter, shown here with my friend Cody Howard whose photo this is. Leaves are far smaller than that of C. currorii as well as much rougher and more crinkled along the margins.

Here is a sizable C. uter living in a large pot at a California nursery. Specimens this size must be a minimum of 30-35 years old, since it takes that long for Cyphostemmas to develop these thick trunks from seed. They are generally not propagated via stem cuttings.

There are many other species of Cyphostemma, some of them strongly caudiciform, but others more like vines or herbaceous perennials. I cannot possibly list all of them and have not seen any of them other than C. currorii in habitat, so I don’t have photos to post. The range of the genus is mostly tropical to subtropical, in dry and seasonally wet climates alike. Most appear to be mainland African although there are some from the Arabian Peninsula and islands like Mauritius and Madagascar in the Indian Ocean. Madagascar, in fact, does have many species, most of them endemic to that biologically unique large island.

Detail of the fruits and leaves of C. uter. They are both notably rough and covered in glandular hairs that are somewhat sticky. This helps prevent browsing by ungulates, in addition to the toxicity caused by oxalic acid.

Online searching can of course reveal the range of interesting shapes and growth habits within the Cyphostemma genus. Some to look for include C. juttae (which I have actually grown several of, all of which froze out in my Arizona winter), C. seitzianum, C. betiforme, C. laza, and C. mappia. I looked at the Wikipedia page on the genus and it says there are approximately 250 species, with a long list of them below the banner; but a quick search on a number of the less prominent species shows nearly no information on or photos of them. I suspect that many of them are vining and less striking in appearance than those large caudiciform types that have their own pages and are well favored by plant growers and collectors. That said, it is clearly a rather fascinating genus.

Macro of the fruits of Cyphostemma juttae. They are more of a pinkish red and much smoother than the glandular-hairy fruits of C. uter.

A large Cyphostemma currorii in Namibia after a year with good rainfall. Photo taken in 2012 by my friend Tim Harvey.

Cody Howard with an absolutely glorious C. currorii circa 2011. Oh how I wish I could grow them!

I do wish I could grow Cyphostemmas in Arizona, but my climate is probably both too cold and too wet in winter for them. It freezes harder here in the northern Sonoran Desert than it does in this part of the Namib Desert, despite the fact that this spot at the base of the Spitzkoppe where my photos were taken is at a higher elevation than I am at. Additionally, winter rains are the norm here in Arizona, and prolonged periods of cold, wet soil combined with several annual cycles of hard frost and even occasional snowfall will probably deter their survival.

I don’t think that wet winters are necessarily completely fatal to C. currorii because plants are successfully grown in such winter rainy/summer dry Mediterranean climates as Cape Town, South Africa and along the mild California coastline, but these areas are also virtually frost-free. In any case, coming across affordable seedlings of C. currorii large enough to test out in my garden is nearly impossible. Larger plants are probably more tolerant of cold and wetness than small seedlings are, but they are very scarce and prohibitively costly, and I would not want to risk losing a plant costing upwards of $1000 or more. So I suppose that I’ll just need to visit them elsewhere, as I must with so many of the earth’s coolest plants. 🙂