Adansonia digitata, the African baobab, is the most widespread tree species of the genus Adansonia, the baobabs, and is native to the African continent and the southern Arabian Peninsula (Yemen, Oman). These are long-lived pachycauls; radiocarbon dating has shown some individuals to be over 2,000 years old. They are typically found in dry, hot savannas of sub-Saharan Africa, where they dominate the landscape and reveal the presence of a watercourse from afar. They have traditionally been valued as sources of food, water, health remedies or places of shelter and are a key food source for many animals. They are steeped in legend and superstition. In recent years, many of the largest, oldest trees have died, for unknown reasons. Common names for the baobab include monkey-bread tree, upside-down tree, and cream of tartar tree.
Description
African baobabs are trees that often grow as solitary individuals, and are large and distinctive elements of savanna or scrubland vegetation. They grow from tall. The trunk is typically very broad and fluted or cylindrical, often with a buttressed, spreading base. Trunks may reach a diameter of , and may be made up of multiple stems fused around a hollow core. The hollow core found in many tree species is the result of wood removal, such as decay of the oldest, internal part of the trunk. In baobabs, however, many of the largest and oldest of the trees have a hollow core that is the result of a fused circle of three to eight stems sprouting from roots. The bark is gray and usually smooth. The main branches can be massive. All baobabs are deciduous, losing their leaves in the dry season, and remaining leafless for about eight months of the year. Flowers are large, white and hanging. Fruits are rounded with a thick shell.
The leaves are palmately compound with 5 to 7 (sometimes up to 9) leaflets in mature trees, but seedlings and regenerating shoots may have simple leaves. The transition to compound leaves comes with age and may be gradual. African baobabs produce simple leaves much longer than most other Adansonia species. Leaflets are stalkless (sessile) to short-stalked and size is variable.
Flowering occurs in both the dry and the wet season. Buds are rounded with a cone-shaped tip. Flowers are showy and sometimes paired, but usually produced singly at the end of a hanging stalk about in length. The calyx is typically made up of 5 (sometimes 3) green triangular bent-back lobes (sepals) with a cream-coloured, hairy interior. The petals are white, roughly the same width and length – up to , and are crumpled in bud. Flowers open during the late afternoon, staying open and fertile for only one night. The fresh flowers have a sweet scent, but after about 24 hours, they start to turn brown and emit a carrion smell. The androecium is white and made up of a long tube of fused stamens (a staminal tube) surrounded by unfused (free) filaments 3–5 cm long. There are a large number of stamens, 720–1,600 per flower, with reports of up to 2,000. Styles are white, growing through the staminal tube and projecting beyond it. They are usually bent at right-angles and topped with an irregular stigma. Pollen grains are spherical with spikes over the surface, typical of the Malvaceae family. Pollen grain diameter is around 50 microns.
All Adansonia develop large rounded indehiscent fruits which can be up to long with a woody outer shell. African baobab fruits are quite variable in shape, from nearly round to cylindrical. The shell is thick. Inside is a fleshy, light beige coloured pulp. As it dries, the pulp hardens into a crumbly powder. The seeds are hard and kidney-shaped with a .06-mm-thick coat. They show long-term dormancy, only germinating after fire or passing through an animal's digestive tract. It is thought that this is because the seed coat needs to be cracked or thinned to allow to water to penetrate before the seed can germinate.
Water storage
Baobab trees store water in their trunks and branches on a seasonal basis as they live in areas of sustained drought and water inaccessibility. The spongy material of the bark allows water to be absorbed deeper into the tissue, as there is rarely enough rain during the wet season to penetrate the litter layer of soil. The U-shaped branches allow for water to trickle down, allowing for maximum absorption over an extended period of time even after the rain stops. The water is absorbed into the vascular tissue of the tree, where it can be moved into the tree's parenchyma cells for long-term storage, or used. A large Baobab can store as much as 136,400 liters of water.