Colours of Wildlife: Carrion Flowers

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Carrion Flowers

Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"


Today I'd like to share with you some photos of the flowers of a group of plants I especially love, the Carrion Flowers, or Stapeliads. All the flowers you see here, are of plants I grew myself. Sadly I've lost a few of these, and I will say why later in this article. But first let's just talk about the entire group: what is a carrion flower?

Fetid Flowers

Edithcolea grandisHuernia blyderiverensisDuvalia corderoyi
Edithcolea grandis
Huernia blyderiverensis
Duvalia corderoyi


First of all the name 'carrion flower' will give you a clue. I've already written about the most famous species of the group here and here. Typical carrion flowers have flowers that look like, well, a piece of carrion. They're frequently hairy, they're coloured and textured to look like raw meat or discoloured, decomposing flesh, or animal droppings, and they've a smell to match. All of this is a ruse to attract pollinators. Typically, the pollinators they wish to attract are flies or bluebottles that lay their eggs on rotting meat or on dung. The flowers don't kill or eat the flies as some people think, they just want their pollination services. They target flies instead of the more typical bees and butterflies, perhaps to avoid competition with regular flowers, or perhaps because they want to profit by not rewarding their pollinators with nectar, as those species do. Also, many carrion flower species grow in dry regions, where there aren't many insects, but most of the ones that do occur, are flies.


What happens with most flies that visit the carrion flowers is this: they land in the centre of the flower, where the smell is strongest, then walk around a bit just to try to see what is going on. They may probe at the flower's surface with their mouthparts. In the very centre of the carrion flower, there is a complex structure called a gynostegium, made by the fused-together male and female sexual organs of the flower. There are 'pockets' inside the gynostegium in which the flower keeps its pollen. The pollen is not in the form of lots of loose pollen grains like in most other flowers, but contained in a neat package called a pollinarium. Each pollinarium contains two separate packets called pollinia, which are connected to each other by a small body or corpuscle.

Huernia insignifloraOrbea dummeriOrbea lutea
Huernia insigniflora
Orbea dummeri
Orbea lutea


Now when the fly probes around, either its mouth, or one of its legs, can get caught in a groove set in the outside of the gynostegium. This groove then guides the leg or mouthpart towards the pollinarium, causing it to snag onto the corpuscle. Further movement then pulls it out, now attached to the fly's leg or proboscis. The fly may have laid some eggs on the flower; the maggots will then hatch out but die because there's no food for them. Whether or not the fly has laid eggs, it will fly away and perhaps land on another carrion flower. If it does, again it might probe around the centre of the flower, and again it might get its now-pollinarium-carrying leg or mouthpart snagged in a groove on the new flower's gynostegium. But what happens now is that the pollinarium itself is detached and sticks to the gynostegium. This is what the flower was after! Now, a long tube will grow from the pollinarium into the gynostegium, at the centre of which are the ovaries containing the ovules. Male cells can now move down the tube into the ovary to fertilize the ovules. And so fertilization happens, and the flower will produce fruits and seeds.


While most carrion flowers smell like rotting meat or excrement, some have somewhat more pleasant odours. Some smell like sweet, over-ripe or rotting fruit, while some smell like mushrooms. Also, while most don't reward the pollinators, there are some that provide them with a bit of sweet nectar.


Carrion flowers are amazingly diverse as you can see from these photographs. Flowers sometimes occur singly, sometimes in clusters of many. Aside from variety in shape, colour and pattern, they vary enormously in size. The smallest ones are mere millimetres (a 25th of an inch) in diameter, while the largest ones reach 40 cm/16". Most are 'open' flowers like these, but there are some with flowers where the tips of the lobes remain fused together, leaving only small 'windows' through which tiny gnats can enter. In some, flies or gnats are 'trapped' inside the flower by downward-directing hairs, allowing them to leave only when the flowers start to wilt. There is one species in South Africa that produces its flowers below the soil surface! We still don't know why, or what kind of insect pollinates them.


The plants themselves also vary enormously. One species from India is a vigorous climber with long stems bearing succulent leaves. The other species are typically small succulents with finger-like stems having a number of ridges forming angles along the stem, with protrusions called tubercles along them. Sometimes the tip of a tubercle bears a spine, or even a soft leaf. But the leaves are always (except in the Indian species) highly reduced. The smallest stapeliads have stems only about a centimetre/half an inch or so long, while the largest species have many-angled, spiny, cactus-like stems that can stand 2 m/almost 7' tall.


Most carrion flowers grow in dry regions, though not many are found in barren deserts. They tend to enjoy some shelter, such as the nooks and crannies between rocks, or the shade and protection of a thorny shrub. Stapeliads are most diverse in Southern Africa, but also occur in most of the drier parts of sub-Saharan Africa, with a second centre of diversity in northeast Africa, and in Madagascar, Arabia, the middle East, and as far as India and Myanmar. A single species is found in the very southernmost parts of Europe.

Classification Confusion

Stapelia kwebensisPiaranthus atrosanguineusStapelia obducta
Stapelia kwebensis
Piranathus atrosanguineus
Stapelia obducta


Traditionally, carrion flowers have been classified as belonging to a specific tribe, the Stapeliae, of the Milkweed family, the Asclepiadaceae. First of all, the family has been moved into another family, the Apocynaceae, a family that used to be mostly tropical trees and shrubs, while the milkweeds typically included many herbs and weedy species including many in temperate regions. But even more radically, there are now signs that the entire tribe of the carrion flowers might be no more than a small part of a single plant genus, Ceropegia! Traditionally, carrion flowers were seen as a sister group to Ceropegia and another genus, Brachystelma. Ceropegia were mostly slender climbing plants with not-very-succulent stems, and very complex and weird flowers. Brachystelma were plants with thin stems and typical leaves on their above-ground parts, and thick tubers or roots below the ground. Brachystelma has amazingly variable flowers, displaying almost all of the shapes and patterns found among the carrion flowers and their relatives, although the flowers are mostly quite small. And then you have the carrion flowers proper, which were classified in many different genera, totalling over 300 species. It is in general fairly easy to recognize the main 'genera' into which they have been classified: Stapelia, Orbea, Huernia, Hoodia, Quaqua, Duvalia, for instance.


But now it would seem that the whole tribe of the stapeliads are 'nested' inside of Ceropegia, along with Brachystelma and a few others! How does this work? Well in classification, the goal is to show the relatedness of species. All living beings on Planet Earth are related by descent from the very first living cell that arose. Species diverged from each other through evolution, one species branching into two, and each of those then branching again, and so on, until today we have millions of different species constituting the 'tree of life'. The more closely two species are related, the more recently the branching off happened. For instance, the closest species to humans today are the chimpanzee and the Bonobo, and our line branched off from theirs about six or seven million years ago (or perhaps slightly more … evidence is still not conclusive). To constitute a naturally-related group, whether a genus, a tribe, a family or an order (at different levels of relatedness) it is necessary that all the members in the group are descended from a single species that branched off from its closest relative at a certain point. Also, such a naturally-related group, also called a 'clade', must contain all the descendants of the original species of the group, and only those descendants of the original species. Such a group is called 'monophyletic', meaning containing a single group of descent. If a group contains only some of the descendants of the original member, it is called 'paraphyletic', and if it contains descendants of several different original members, it is called 'polyphyletic'. Biological classification tries to avoid both of these, though in popular language we do often group things together like that – for instance our notion of a 'fish' includes bony fish and sharks, which are two fairly distantly related groups, while not including reptiles, amphibians, birds and mammals, which are actually nested inside the bony fish, being descendants of a specific group of bony fish, and being more closely related to all other bony fish than sharks are to any bony fish.


So … the situation with Ceropegia, Brachystelma and the stapeliads seem to be this: all of the stapeliads, and all of the Brachystelmas, are descended from some species that likely doesn't exist any more but which would have been in classified in the genus Ceropegia. So … they are all closely related to certain other members of Ceropegia (the ones closest to the species from which they descended). Other Ceropegias would be less closely related to them and also to each other. So Ceropegia would then be a paraphyletic group. Keeping Ceropegia a monophyletic group means having to include all Ceropegia-descendants, which means including all of Brachystelma and all the stapeliads. Now the only way to do this would be to classify them all under Ceropegia, or to break up Ceropegia into many genera or even into tribes. Whichever way, it would be messy and thorny. This and other reclassifications are sure to lead to much more debate in botanic circles.

Growing Carrion Flowers

Hoodia currorii lugardiiDuvalia politaHuernia zebrina magniflora
Hoodia currorii lugardii
Duvalia polita
Huernia zebrina magniflora


I've touched on growing carrion flowers in my previous articles. The giant and variegated carrion flowers are pretty much the easiest of them all to grow. Many of the others are in fact rather touchy, which is why I've lost so many. They are very susceptible to fungal infections. As I've said, these plants grow mostly in dry regions. Some grow where there's more rain, but in those cases they grow in shallow, well-draining soils. In soil that remains moist, the fungus can grow and attack the roots and stems of the plans, causing black spots and rotting. Sometimes the whole plant turns to mush. To try to limit this, plants need to be planted in a very well-draining, porous soil mix, and to be watered sparingly – ideally, watering and then letting the soil dry out completely before watering again. Plants are also attacked by scale bugs and by white mealy bugs. These can be controlled by inspecting the plants and removing the bugs; above-ground stems can be brushed with a stiff toothbrush, the roots should be inspected each year, when re-potting plants. It is always a good idea to regularly re-pot plants to make sure they're healthy as well as to multiply and propagate them. Most species can be propagated vegetatively, by detaching pieces of stem and then rooting them. Always let the stems 'rest' for a week or so in a shady spot before planting them, to allow scar tissue to form over the wounds, to safeguard them against bacterial infections.


With the proper precautions, stapeliads can be grown without too much difficulty. They can be grown from seeds as well, which may however not be easy to come by. I suggest that if you're really interested, to start with the easiest species, make sure you can take care of them for a year or two, and then slowly expanding your collection with more and more difficult species as your experience grows. They're extremely satisfying plants to grow, to have around, and to see in flower.

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Willem

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