The Great Baobab Enigma
By Ian Pringle, Waterberg Bonsai Club.
The African Baobab, Adansonia digitata, is one of eight species of the remarkable Baobab genus, Bombacacaea family. Adansonia digitata is indigenous to Africa and is found in thirty-one countries of Africa (Pakenham, 2004). A further six species (A. grandidieri, A. suarezansis, A. rubrostipa, A. madagascarensis, A. za and A. perrieri) are found only in Madagascar, regarded by many botanists as the birthplace of the Baobab. Although Adansonia digitata is found in Madagascar it is strictly speaking an ‘alien’ there, having been recently introduced to the country from Africa. An eighth species, Adansonia gibbosa, is endemic to Australia (op.cit.). Various baobab specimens have been transplanted elsewhere by man, notably to the West Indies, Florida and India.
The natural distribution of the baobab begs the question as to why there are six species of baobab unique to Madagascar and only two in the rest of the world, 15 000 kilometres apart, one unique to Africa and a further species unique to Australia! A study of the flowers of the Baobab has shown that the genus evolved in the last 17 million years (Baum, 1995), well after continental drift should have
isolated the genus. The Gondwana super-continent, which once embraced what are now South America, Africa, India, Antarctica, Madagascar and Australia, started to split up during the late Jurassic, at least 150 million years ago. If the spread of the Adansonia genus occurred before the split-up of Gondwana one would be dealing with a living fossil, approaching the age of the Ginko biloba. The Ginko-phyllum, as indicated from fossils found near Vereniging, is at least 250 million years old (MacRae, 1999). One would also expect to find some Adansonia species in the other remnants of the super-continent, South America or India. Antarctica is simply too cold today for them to have survived even if they had been present on the polar continent in earlier times. The natural distribution remains an enigma.
Baum himself postulated that the intrepid baobab ancestors sailed from Madagascar in their own seed pods several million years ago, one baobab flotilla landing in east Africa, the other in west Australia (Pakenham, 2004). A short trip from Madagascar to Africa seems possible but one all the way to Australia is very unlikely.
A possible solution lies in the ‘out of Africa’ theory. Man may have carried the seed with him when he left Africa to populate the world. Adansonia digitata is a great provider (Pakenham, 2004) and would have been valued by the indigenous people. But there is no evidence of remnants of Adansonia between Africa and Australia albeit that Adansonia will obviously not fossilise. A study, using molecular biology or molecular genetics to be more precise, could determine just when the two species, A. digitata and A. gibbosa, separated. A result in the region of 50 000 years ago would favour the out of Africa theory but a result an order of magnitude greater (or more) could mean you have a living fossil in your bonsai collection.
And so the great baobab enigma remains…
References:
Baum, D. (1995). A Systematic Revision of Adansonia (Bombacaceae), in Ann. Missouri Bot. Gard., pp 440-470.
MacRae, C. (1999). Life Etched in Stone. Geol.Soc. of S.Afr. 305p.
Packenham, T. (2004). The Remarkable Baobab. Jonathan Ball Publishers (Pty) Ltd.143p.