Africa's savannas are characterized by wide expanses of grasses and scattered trees. To visitors it can sometimes seem as if there are few other flowers in the savannas, but most bloom in the rainy season when tall grasses often obscure them, or they flourish only in areas near rivers and waterholes. Many native species are oddities of twisted limbs, thorns and weird attractions for specific animals, but for all their strange beauty, savannas are richer in wildlife than any other biome on earth.
The typifying feature of savannas is a park like spacing of trees within an endless sea of grasses. The umbrella thorn (Acacia tortillis), is the tree people most often think of when thinking of the African savannas. It is a wide-spreading shade tree that dots the plains, and offers protection to animals when the summer sun gets too hot. All but the giraffes and humans avoid its tiny leaves, seedpods and flowers, though as a member of the pea family, they are edible and tasty. Two types of thorns make it too formidable for other animals to dare.
The whistling thorn (Acacia dreparalobrium) is another thorny acacia, but this one has a couple of "twists." Along with the usual long thorns, the tree develops modified thorns called stipular spines, which swell to accommodate four species of stinging ant. The ants live inside the swellings and swarm out to sting any other creatures who dares nibble on their tree. When dead and dry, the holes in the stipular spines make a whistling sound when the wind blows across them---thus the name. Some species of ant also prune their host tree to prevent other ant species from taking up residence. The pruned branches leak a nectar that feeds the ants.
Among the other trees of the savannah, is the odd, upside down tree---the Baobab (Adansonia digitata), which really does look as if it was accidentally planted wrong way up, with roots waving in the air. Another is the beautiful but dangerous Candelabra tree (Euphorbia ingens), with sap that will cause an instant blister upon contact with skin, and will blind you if it gets in your eye.
One savannah tree that does behave itself is the Manketti tree (Schinziophyton rautanenii). Not only does it look like an ordinary deciduous tree, but it produces fruits and important nuts, rich in oil.
Grasses comprise the largest area of the savanna and account for the majority of plant species represented. Elephant Grass (Pennistum purpureum) is among the tallest of the native grasses, reaching up to 10 feet in height. With its razor-sharp leaf edges it makes nearly impenetrable stands along rivers and other waterways and is a favorite nesting species for birds. It has 9-inch plume like flowers, and has been introduced to the United States (especially Florida) as an ornamental species, but is becoming invasive.
Another U.S. invader that originated in Africa, (not Bermuda) is Bermuda grass (Cynodon spp.). Imported as a turf species, it thrives in sun. Red grass (Themeda triandra) is a tall, slender forage crop for wildebeests (though it is eaten usually only after other grasses are exhausted). It has a bunching habit and grows much like wheat in large fields of widely spaced clumps. One of the few shorter grasses is Pan Dropseed (Sporobolus ioclados). It is heavily grazed by a variety of herbivores.
Among the many herbaceous plants of the savannas, are several that can be found in nurseries and gardens here in the United States. Many hibiscus species (particularly Hibiscus cannabinus); coleus (Coleus spp.); and one particularly pretty garden plant, the red hot poker (Kniphofia uvaria ) are natives of the African savanna.