The Phyto-Philes: Pterodiscus ngamicus, Part 1
Created | Updated Nov 9, 2014
Pterodiscus ngamicus
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!"
This time I present to you a quite undeservedly poorly-known plant species. Even here in South Africa hardly anyone knows about it. It doesn't even have a common name! Its scientific name is Pterodiscus ngamicus. The name means 'Winged Disc of Ngami'. The 'winged disc' part refers to the fruit of this plant, which has four flat, semicircular 'wings' surrounding the fruit capsule. These fruits look very similar to those of a group of trees widespread over here, the Combretums or bushwillows. But Pterodiscus is not at all closely related to these trees. It is actually a member of the Sesame Family, which includes the plant from which we get sesame seeds. Pterodiscus seeds are quite similar, though I haven't tried eating them! They're way too precious – I plant them.
Oh, and the 'Ngami' part refers to a region in our neighbour country of Botswana. This species occurs in the northern parts of South Africa, and also in Namibia, Botswana, Zimbabwe and Mozambique. There are a few other species of Pterodiscus in Southern Africa, though some of them might turn out to be variants of Pterodiscus ngamicus. One form that is very distinct and occurs in the same region is the lovely Pterodiscus speciosus with large, purple flowers. I have been experiencing difficulties with cultivating it … when I've straightened them out, I'll write an entry for that one! Meanwhile, Pterodiscus ngamicus is proving easier to grow, and is also a very pretty plant. Apart from Southern Africa, the genus Pterodiscus also occurs in East Africa, especially around the 'Horn of Africa'. It has only a dozen or so species, if that much. It is one of a few members of the Sesame family that displays succulence. The largest and most succulent species are the Sesame Bushes, which are actually small to medium-sized, fat-trunked trees. Most members of the Sesame family have attractive trumpet-like or foxglove-like flowers.
This particular Pterodiscus has, as I've hinted in the previous paragraph, several forms. The one I have here is the typical form. It has a short, fat, basal trunk, in the wild often partly or wholly subterranean. It tends to grow in sand or loose soil. The basal trunk stores water and nutrients, surviving the long, dry winter, and sending out fresh new shoots each summer. (This kind of basal stem sending out annual shoots is called a caudex, and plants with caudices are called caudiciforms.) The shoots are thin and bear the leaves, flowers and fruits. The basal stem grows up to 10 cm/4" in diameter, and the annual shoots reach 30 cm/12" in length. The leaves vary from being oval with smoothly rounded edges, to deeply lobed. They are usually a greyish-green, with light, almost white, undersides. The flowers appear early in the spring, crowded towards the tips of the stems. The photo here is one of my specimens, showing clearly all of these features. I include for you some close-up shots of flowers too. These are the typical ones, the lobes being purplish or pinkish, and the inside of the tube yellow. As you can see the flowers are 'fuzzy', covered with short, soft, white hairs. They reach about 5 cm/2" in length. They're insect-pollinated, though I haven't yet determined which insects pollinate them.
The flowers vary in colour. Some are much paler than these, creamy, almost white. Some are pale to bright yellow (although those might turn out to be a different species). In Zimbabwe and other northern regions, the flowers may be almost entirely bright orange-red. An orange, Namibian form is sometimes considered a different species, Pterodiscus aurantiacus. One form with very similar flowers is sometimes considered a separate species, Pterodiscus luridus, but these have stems that, at least in the photos I've seen, have a different surface texture.
In my region, Pterodiscus ngamicus is found mostly in grassland, savannah or bush with sparse groundcover. It cannot compete with tall grasses or dense herb growth. It can grow in the open or in light shade of surrounding bushes. It favours hot and fairly dry places, with sandy or gritty soil. The plants are quite small and inconspicuous, but if you have an eye for them, you can spot them easily. They're delightful when flowering. Here is a photo of one growing in Sekukuniland, a region to the south of my home town of Polokwane, with lovely, deeply-coloured flowers. It is also a treat to find them covered in the winged fruits. Here you see a photo of another one in the wild, bearing lots of fruits, and with a few dried ones lying on the ground in front of it. The thin, papery wings cause them to be blown about the savannah by the wind, so distributing the fruits and their seeds.
Want to know more about this fascinating plant? See Part 2 of this article.
