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Wednesday, March 20, 2013

Baobab (Adansona digitata)

Family Bombacaceae
Regarded as the largest succulent plant in the world, the baobab tree is steeped in a wealth of mystique, legend and superstition wherever it occurs in Africa. It is a tree that can provide, food, water, shelter and relief from sickness.


Description

Often referred to as 'grotesque' by some authors, the main stem of larger baobab trees may reach enormous proportions of up to 28 m in girth. Although baobab trees seldom exceed a height of 25 m. The massive, usually squat cylindrical trunk gives rise to thick tapering branches resembling a root-system, which is why it has often been referred to as the upside-down tree. There is a tale which tells of how God planted them upside-down. Many traditional Africans believe that the baobab actually grows upside-down.
 The stem is covered with a bark layer, which may be 50-100 mm thick. The bark is greyish brown and normally smooth but can often be variously folded and seamed from years of growth. The leaves are hand-sized and divided into 5-7 finger-like leaflets. Being deciduous, the leaves are dropped during the winter months and appear again in late spring or early summer.


The large, pendulous flowers (up to 200 mm in diameter) are white and sweetly scented. They emerge in the late afternoon from large round buds on long drooping stalks from October to December. The flowers fall within 24 hours, turning brown and smelling quite unpleasant. Pollination by fruit bats takes place at night.
 The fruit is a large, egg-shaped capsule (often >120 mm), covered with a yellowish brown hairs. The fruit consists of a hard, woody outer shell with a dry, powdery substance inside that covers the hard, black, kidney-shaped seeds. The off-white, powdery substance is apparently rich in ascorbic acid. It is this white powdery substance which is soaked in water to provide a refreshing drink somewhat reminiscent of lemonade. This drink is also used to treat fevers and other complaints.


This tree is slow growing, mainly due to the low rainfall it receives.
 Distribution

The baobab tree is found in areas of South Africa, Botswana, Namibia, Mozambique and other tropical African countries where suitable habitat occurs. It is restricted to hot, dry woodland on stoney, well drained soils, in frost-free areas that receive low rainfall. In South Africa it is found only in the warm parts of the Limpopo Province.

It may however be cultivated in areas of higher rainfall provided they are frost free and don't experience cold winters.

Derivation of name and historical aspects

The name Adansonia was given to this tree to commemorate the French surgeon Michel Adanson (1727-1806); the species name digitata meaning hand-like, is in reference to the shape of the leaves.

The baobab used to belong to the family, Bombacaceae, but this is now generally regarded as a subfamily of Malvaceae. Bombacaceae is tropical with about 21 genera and 150 species. It is host to some very interesting species. The balsa tree, Ochroma pyramidale from South America, is well known for its exceptionally light wood of 160kg/m2. The durian, Durio zibenthinus, is a popular and apparently delicious fruit from the east, which although being so tasty, has such a terrible odour that it is banned from hotels. The silk floss tree (Chorisia speciosa or Ceiba insignis) is a very widely planted ornamental tree in South Africa and is a sight to behold when it is in full bloom with its large, usually pink flowers.

The family has a number of different baobab-type trees, also of the genus Adansonia. With one species in Australia and four species native to Madagascar, the most spectacular, A. grandidieri, reaches a staggering 40 m in height, only bearing branches at the very top of the tall, thick trunk. The family is also well known for the kapok tree, Ceiba pentandra, which is native to the equatorial rain forests of South America, Africa and India. The kapok tree has been widely cultivated in the tropics, for the prized kapok fibre produced by the seed pods, which was used to stuff pillows among other uses.

 A number of significantly large, historical baobab trees can be seen in the Limpopo Province:


• The Sagole Baobab is recorded as being the biggest tree in South Africa with a stem diameter of 10.47 m, a height of 22 m and a crown spread of 38.2 m. It grows east of Tshipise.

• The Glencoe Baobab near Hoedspruit is probably the second largest and bears several trunks. It has a stem diameter of 15.9 m, a height of 17 m and a crown spread of 37.05 m. This tree has dates carved on the stem from 1893 and 1896.

• The Platland Baobab that grows near Duiwelskloof, today houses a pub. It has a stem diameter of 10.64 m, a height of 19 m, and a crown spread of 30.2 m.

• The Buffesldrift Baobab which is in the Makopane District, has a distinct trunk with a diameter of 7.71 m, a height of 22 m and a crown spread of 30.2 m.

Ecology

Bats primarily pollinate the large white flowers with their ruffled petals at night, although many different insects and other creatures such as birds will visit the sweetly scented flowers. The flowers, being white, are more visible at night and being sweetly scented also help to attract a wide variety of potential pollinators. The seed capsule does not split open, instead it hangs on the tree until it gets blown off by wind or gets collected by monkeys, baboons or people who all enjoy the soft powdery substance that covers the seeds. The seeds are not generally eaten by animals and are discarded, thus effecting dispersal.

 Uses and cultural aspects

Large baobab trees with hollow stems have been used by people for centuries for various purposes including houses, prisons, pubs, storage barns, and even as bus stops! A big tree in the old Transvaal region is recorded as once being used as a dairy.

Another tree near Leydsdorp was used as a bar (known as the Murchison Club) and utilized by prospectors and miners during the gold rush of the late 19th century. One such tree in the Caprivi Strip was converted into a toilet, complete with a flushing system.

Rainwater often collects in the clefts of the large branches, and travelers and local people often use this valuable source of water. It has been recorded that in some cases the centre of the tree is purposely hollowed out to serve as a reservoir for water during the rainy season. One such reservoir was recorded as holding 4 546 litres of water. A hole is drilled in the trunk and a plug inserted so that water can be easily retrieved by removing the plug. The roots of the baobab can also be tapped for water.

African honey bees (Apis mellifera) often utilize hollows in the baobab to make their hives. One can often see a 'ladder' of pegs hammered into the trunk which is used by seasonal honey harvesters to gain access to the hives.

The leaves are said to be rich in vitamin C, sugars, potassium tartrate, and calcium. They are cooked fresh as a vegetable or dried and crushed for later use by local people. The sprout of a young tree can be eaten like asparagus. The root of very young trees is also reputed to be edible. The seeds are also edible and can also be roasted for use as a coffee substitute. Caterpillars, which feed on the leaves, are collected and eaten by African people as an important source of protein. Wild animals eat the fallen leaves and fresh leaves are said to be good fodder for domestic animals. The fallen flowers are relished by wild animals and cattle alike. When the wood is chewed, it provides vital moisture to relieve thirst, humans as well as certain animals eat it in times of drought.

There are many legends and superstitions surrounding the baobab tree. For example, it is believed that an elephant frightened the maternal ancestor of the baobab. In some parts the baobab is worshipped as a symbol of fertility. It is a belief among certain people that spirits inhabit the flowers of the baobab and that any person who picks a flower will be eaten by a lion. It is also believed that water in which the seeds have been soaked will offer protection against attack by crocodile, while sucking or eating the seeds may attract crocodiles. It is also believed that a man who drinks an infusion of the bark will become strong. In some areas a baby boy should be bathed in such a bark infusion, as this will make him strong; however, he should not be bathed for too long or he may become obese. It is also important that this water does not touch his head for this could cause it to swell. When inhabitants move from one area to another they often take seeds of the baobab with them, which they plant at their new homestead.

The bark on the lower part of the trunk often bears scars caused by local people who harvest and pound it to retrieve the strong fibre. The fibrous bark is used to make various useful items such as mats and ropes, fishing nets, fishing lines, sacks as well as clothing. Although the bark is often heavily stripped by people and elephants, these trees do not suffer as a normal tree would from ringbarking. Baobabs have the ability to simply continue growing and produce a new layer of bark. The wood of the baobab is soft, light yellow and spongy, and although it has been recorded as being used for making boxes, this does not seem to be a widely used practice.

Many references have made mention of the exceptional vitality of this tree, noting that even after the entire tree is cut down it simply resprouts from the root and continues to grow; the same is noted of trees which have been blown over in storms. Despite this remarkable vitality, when a tree dies it collapses into a heap of soggy, fibrous pulp. Stories exist of how such quickly decomposing trees spontaneously combust and get completely burnt up.

More than 260 years ago baobabs were apparently successfully grown in England and had reached heights of 5-6 m, but were all destroyed in the heavy frosts of 1740. Surprisingly few baobabs have found their way into cultivation, possibly due to their reputation of being exceptionally slow growing.

The baobab was declared a protected tree under the Forest Act in South Africa in 1941.

Determining the age of baobabs: Much speculation in literature over many years have made certain estimates of the age of certain large trees and their rate of growth. More recent work using carbon-dating techniques as well as the study of core samples showing growth rings, suggest that a tree with a diameter of 10 m may be as old as 2000 years.