Text and photos by Ida K. Rigby, for Let’s Talk Plants! December 2022.
Okavango Delta Wetlands, Part 2
In the last column we glided through the Okavango Delta’s marshes and swamps in mokoros…
…for a quiet, close-up look at the flora and fauna on the termite mound generated islands.
We also noted the dramatic changes that have occurred in the Delta over a period of six southern African winters due to climate change and a powerful earthquake. We’ll continue our exploration of the wetlands, then in another column turn to the permanently dry areas of the Delta.
One of the trees that occupies the islands of the Delta and riverine areas of southern Africa is the sausage tree, Kigalia africana.
The seed cases, which look like light weight luffa sponges can weigh nine pounds; you do not want to be under one when it falls.
Nonetheless, villagers plant sausage trees near their homes as lightning rods. Monkeys and epauletted fruit bats…
…and hawk moths pollinate the velvety, maroon, trumpet-shaped flowers, which are full of nectar.
The flowers open at night, and the petals fall the next day after turning from yellow to maroon. Once one flower on a stalk is pollinated the rest of the flowers are no longer receptive to pollination. Kudu browse the leaves, and bush pigs and baboons eat the fruit.
Sausage tree leaves produce a green dye for palm leaf baskets; the blossoms produce a brown dye; the roots yield a yellow dye. (We’ll discuss these baskets woven by women in another column.) The fruit is fermented to make beer. It also has medicinal uses, as a purgative for example. The lightweight wood has been used for oars and canoes. Creative camp staff use the seed cases for decorative signs.
The strangler fig, Ficus burkei, grows in savannas and forests and on riverbanks and termite mounds. It was named after Joseph Burke, a nineteenth century plant collector. On one visit to the Delta a fifty-year-old strangler fig grew just outside my tent…
… the tree is just to the left of my tent. A strangler fig most often starts its life when a bird drops a seed high up in a tree. The seed germinates and the plant sends down aerial roots. Over the years the ficus encases and “strangles” the original tree. The hollow created after the original tree rots shelters all manner of small mammals, birds and reptiles. Strangler figs can also be terrestrial; the trees on the bank in front of my tent grew from seeds that germinated in the soil.
Its seeds can also lodge and grow in rocky crevices. A mature strangler fig can have a very sculptural buttressing system. Its broad leafy crown shelters birds, figs are eaten by insects, fruit bats, baboons and warthogs. Humans pound bark fibers into rope and use the sticky, non-toxic latex used for trapping birds and hares. (The treessa.org website has a fascinating description of how wasps pollinate figs, which made me finally understand why the fruit on my Mediterranean fig trees rot.)
In permanently dry areas of the Delta the strangler figs can look scrappy.
These photos of a leopard climbing a termite mound to ascend a tree illustrate the two ways a strangler fig can grow. The very straight, smooth barked trunk in the left foreground is a terrestrial strangler fig growing directly out of the termite mound. A few small twigs with very green leaves are growing on its left side. The mound is also home to stranglers that began aerially and are winding around the other tree trunks. (The wild date palms at the base of the mound will figure in another column.)
The photos of semi-aquatic red lechwe illustrate the multilayered flora of the flood plains, marshes and swamps.
Reeds, sedges and grasses grow in various depths of water: The Papyrus cyperus inhabits the deeper water, Miscanthus and Typha capensis the shallows, Phragmites australis—up to 20 feet high—edges the islands. The Typha capensis anchors itself in the mud with its creeping rhizomes. The “cat tail” inflorescences have male flowers at the top and female flowers in the lower part, which capture pollen. The plants shelter fish and frog hatcheries and wetland birds’ nests. The rhizomes are used to treat venereal disease and ease the labor of women giving birth. It is also used to treat dysentery. (One of the most fascinating chapters our San Diego Horticultural Society Book Club has read is the chapter on the myriad of uses Indigenous North American have for cattails in Robin Kimmerer’s Braiding Sweetgrass.)
The next series of photos of a marsh antelope, the extremely shy sitatunga, is included simply because it falls into the category of “I’ll never see one of those.”
Curious, this sitatunga ventured closer and closer, then suddenly turned and dashed into the papyrus. The sitatunga is an aquatic antelope, meaning it lives in the waters of marshes and swamps. It has a split hoof and a “second hoof.” Between the two “hooves” is a pad that expands when it flees a predator. The gives the sitatunga purchase in sandy mud and facilitates a quick escape from predators. They make papyrus beds to sleep on, and females build beds for their young. By contrast, the semi-aquatic red lechwes forage on the wet flood plains and edges of marshes and also spend time on dry plains, which sitatungas do not.
Elephants love the grassy marshes and edges of papyrus rafts. They uproot reeds and grasses then swing them about to dislodge the mud before swallowing them.
One afternoon we were following a wide, flowing hippo channel, rounded a bend and just across the channel a magnificent bull was peacefully munching on papyrus.
Bulls (when not in musth) are far more tolerant of humans than females who are wary because of their own calves and those in their breeding herd. We gave a wide berth to females. This thirty year old bull, in his prime, delicately grasped the papyrus with his trunk’s “fingers,” and folded and broke the stalks into tasty, tasseled morsels. The secretions running down his cheeks from his temporal glands are a sign of stress, not because of our presence, but because of the persistent drought. He suddenly took serious note of us and lifted his trunk to sniff who or what we were (they are quite nearsighted). Elephants have an incredibly powerful sense of smell that compensates for their nearsightedness. He remained calm, but kept an eye on us, as he ambled closer and headed away along the edge of the papyrus island, turning periodically to check on our location.
The light was fading, so we started home. En route we passed some hippo ponds and had a small encounter with a hippo, which will begin the next column on the Delta.
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