Euphorbia clivicola – a Ridiculously Endangered Succulent
Willem says: 'The Phyto-Philes are for plant lovers of every size and shape, colour and flavour. As with my Colours of Wildlife column, I'll be featuring one species per article, illustrated with sketches, paintings, and/or photos. Over time I hope to be showcasing the amazing diversity of weird and wonderful plants that occur in South Africa, while also from time to time looking at the flora of other countries. While featuring many spectacular species, I'll not be neglecting the smaller, more humble kinds that are nevertheless fascinating in their own right.'
Today I bring you something about which I'm very happy and sad. This is Euphorbia clivicola, and instead of paintings I again present to you some photos that I've taken myself that illustrate this species very well. This is a succulent plant that occurs close to where I live … in fact, it's just half an hour's hike away from my house. These plants grow in low hills that stretch eastwards from the edge of the suburb of Ster Park. They grow in rocky patches, often wedged in cracks in the rocks. The habitat is fairly open savannah grassland, experiencing occasional fires.
The first time I encountered these plants was many years ago on a hike. I was utterly delighted to find them. I had never before seen small euphorbias like those in the Polokwane region. We mostly have large euphorbias, the tree-like ones like these. Euphorbia clivicola is very, very different. It is a low plant, growing from a deep root-tuber, with short, thin stems crowded together, most of the time forming a spreading, cushion-like mass. I show to you three different plants here: the first, growing in the shade of a tree squeezed between some rocks, shows the stems much more elongated than usual. The second photo shows a plant more exposed, with tufts of grass growing with it, forming a denser cushion of short stems. The third photo shows a particularly large cushion, growing in an open patch of grassland, with hundreds of stems. This specimen must be ancient, with a huge root tuber.
What I would like to emphasize here is the uniqueness of this species. Euphorbia is a huge genus of plants containing about 2 000 known species, and in South Africa alone there are over 250 known forms, and many more likely to still await discovery. They vary from tiny herbs and weed-like forms to the great tree-like species, with almost everything imaginable in between. The species Euphorbia clivicola belongs to a large group of low, shrubby euphorbias. And yet, although many relatives like Euphorbia schinzii, Euphorbia enormis and Euphorbia limpopoana are found fairly close by, they are very different from clivicola. Clivicola is a lush and plump-looking euphorbia, its spines not particularly numerous or long. The stubby, finger-like stems stand out, never appearing withered or shriveled, and the dense, cushion-like growth form enhances the appearance of succulence. Also, the clumps are always a fresh, light-green colour, sometimes with a hint of yellow. There are rarely any dry or dead stems to be seen in a clump. By contrast the other small euphorbias in the region are much more spiny-looking, much more scruffy and scratchy, usually being darker in colour, often with relatively skinny-looking stems that are often shriveled, and frequently there are dead, dry stems in and around the clumps, which tend to grow high like small shrubs rather than dense, low cushions. Make no mistake, they also have their craggy charm as well, but I want to stress how different this one is, with its much more 'classic' and elegant appearance. It probably has to do with the hills where it grows having quite a mild climate compared to the harsh, hot and dry climate where most other local small euphorbias grow.
What is also very nice about these small euphorbias is that they grow pretty much in the town of Polokwane. Most residents of my town are extremely ignorant of plants. Those with some interest know the large tree-like euphorbias because they are so conspicuous and their strange forms are hard to ignore. But almost no resident is aware of the existence of the smaller Euphorbias. And here, right at the edge of my suburb, I have this fine colony of small euphorbias that I can show to them! There happen to be a few of the large tree-like euphorbias growing in those hills as well. So in a single place I can point at one plant, and at another growing close by, to vividly illustrate the diversity to be found in this huge group of succulents.
Another very interesting thing is that, hiking just a short distance further, yet another colony of small euphorbias can be found. These are Euphorbia groenewaldii, and they are again extremely different from the clivicolas. They grow in what looks like a drier region of hills – even if this region is just on the other side of a road from the clivicolas! They also look craggier … they are very spiny and have longer, stouter stems, that are spiraled like corkscrews! And these, compared with the clivicolas, again do an excellent job to illustrate the potential of biodiversity. Given a tree-like candelabra euphorbia, a clivicola cushion, and a corkscrew groenewaldii, all placed alongside each other, a novice would never guess that all three belong to a single genus.
How could this be? It seems that the plants belonging to the genus Euphorbia are almost absurdly adaptable, able to mold their stems into almost any sort of shape, able to rapidly change their growth form to adapt to a particular region. That they are related becomes evident when you look at their flowers. Euphorbias have a structure called a cyathium, which is an inflorescence with severely reduced flowers, surrounded by an envelope or cup-like structure called an involucre. There are sometimes short petal-like bracts around the cyathium, which are sometimes brightly coloured, looking like the petals of a regular flower although they're actually different structures. While the cyathia of euphorbias also display amazing diversity, they are all similar enough to each other to show their close relationship. A quickly demonstrable feature of them all is the milky latex they copiously exude from every wound. This is toxic and an excellent defense of the plants against browsers.
Euphorbias simply seem to be able to adapt and diversify amazingly. But that brings us to the sad part. Euphorbia species adapt amazingly well to a very specific habitat. Which now leads to the situation that many of them are restricted to these very specific habitats. They're found there and nowhere else. This is the case with the clivicolas. They grow on these hills in eastern Polokwane … and in another hilly region about 38 km/24 miles to the west. And nowhere else! This situation is found with many other Euphorbia species … you'll find a species, a very unique one, in a single, small region … or two, or three small regions … and nowhere else. This makes them extremely vulnerable … as I'm about, to my own sadness and sorrow, to recount in detail as it affects Euphorbia clivicola.
Let's start with the other colony, the one 38 km away. This colony is in fact in a nature reserve, and has been known since the reserve's proclamation. The plants seemed safe. In 1986 there were 1500 individual plants known in that population. But in 1996 there were only 165! In 2005 there were only 58! And in the most recent survey they found ONLY TEN! What happened?
What happened is that the environmental management policy of the reserve focused on large mammals … it is a game reserve specializing in large antelopes, including rare ones like roan and sable. But what's best for antelopes is not what's best for euphorbias. The low tufts of the clivicolas need frequent fires to trim back the grass and allow them room to grow. In the nature reserve fire was restricted and the grass was allowed to grow tall for grazing mammals. The euphorbia tufts became overshadowed by the grass, grazing antelopes trampled the clumps, and there were no areas of clear ground where their seeds could germinate. The reserve management was repeatedly informed of the problem but did nothing. This is part of a nature conservation attitude that still focuses almost exclusively on large, spectacular mammals, while ignoring the little things … and yet, those little things are what far and away constitutes the majority of the incredible biodiversity of South Africa.
The colony in the nature reserve now appears to be doomed. Ten plants down from a thousand five hundred in less than forty years … and with natural propagation shut right down. This means that the colony in the hills east of where I live now constitutes the last meaningful stronghold for the species. The euphorbias are still numerous and grow along with many other pretty and interesting plants. Here you see a small one with some other species that grow with it: a deep purple flowering Aptosimum lineare, a round-leaved, succulent Kalanchoe paniculata, the lower dry leaf-skirt of a large Aloe marlothii, grasses and a slender twining herb. This photo also shows the openness of the substrate, with lots of empty patches of ground in between the plants, making it possible for seeds to germinate and grow into new individuals.
On the surface of it, it doesn't look too bad. The last time I thoroughly explored the hills I found a great number of plants, I am fairly sure they number in the hundreds. But again … the situation historically shows a different picture. In 1986, the colony of plants in Pietersburg (what Polokwane was called back then) numbered about 3000! By 1996 they had dwindled to 382. A census in 2005 though found about 650 plants. An increase since 1996 does seem to show some hope for them. But still, that is only about a fifth as many as existed in 1986.
And then you have to consider the nature of the threats. Polokwane is a rapidly growing city. When we came to Pietersburg in 1980, we were on the outskirts and there was a vast wild region to the east of the suburb. That was where the euphorbias grew. Since then the suburbs have been expanding eastward. Streets, houses, shopping malls are taking the place of what was once pristine savannah and grassland. They are building houses more and more into the hills. Those are big, sought-after houses, with very nice views from up there, and from the houses the roads are now built into the hills as well. Many folks enjoy riding their quad bikes into the hills, riding right over the little euphorbias. The municipal government knows about the euphorbias and are supposed to leave the hills undeveloped. But still, with all the development around the hills, they cannot remain unaffected. A ridiculous amount of garbage is dumped in and around them. There's rubble and waste from the building projects. Often garbage is dumped right on top of the euphorbias. But another factor is that all the waste is attracting rats and mice, and these seem to be able to tolerate eating the fruits of the clivicolas, in spite of the toxic latex. This of course reduces the number of seeds that the euphorbias distribute.
But there is hope. The habitat up in the hills is still very favourable, being open with short grass and lots of crevices between rocks and stones in which seeds can germinate. To some degree, people are also dissuaded from going on joy rides up there, because of the numerous hobos who squat in the bushes around there and occasionally attack people (not that I've ever been attacked, nor have I even seen these supposed hobos although once I did come across an abandoned hobo hideout). But still, the situation for the euphorbias is extremely precarious, and what happened in the nature reserve shows just how rapidly even a healthy-looking population can be wiped out by what might look like minor factors.
Read more about the Euphorbia and its habitat on the next page