There are 8 species of baobab trees in the world, with 6 species found on the island of Madagascar in the Indian Ocean, one species in Africa, and one species in Australia. The origin of this tree species is a topic of great interest to many people.
Baobab is a key tree species often referred to as “the tree of life” because it supports the surrounding ecosystem, providing food and shelter for various animal species. Baobab trees can reach enormous sizes in both height and diameter, while their extensive root systems help slow down soil erosion and recycle nutrients. The largest species can tower over the undergrowth.
Baobab trees in the Tanami Desert, Australia. (Photo: sciencenews.org).
When you encounter a large baobab tree in Africa, it truly resembles an “Avatar Tree of Souls” – the dwelling place of the Na’vi people in the movie Avatar. The enormous trunk is a hollow wooden cylinder that holds a massive quantity of water. Some of the largest and oldest baobab trees in Australia are estimated to contain over 100,000 liters of water.
According to the latest research by an international team of scientists, the baobabs we see today all originate from Madagascar. To reach this conclusion, plant geneticists from the Wuhan Botanical Garden in China and the Royal Botanic Gardens, Kew in London (United Kingdom) compiled and studied the genomes of all 8 species of baobab in the world. The research team stated that baobab trees began to evolve into distinct species approximately 21 million years ago. Subsequently, 2 of the 8 species migrated to Africa and Australia over the past 12 million years before going extinct in Madagascar.
Within the genomes of the baobab species, researchers found evidence of ancient hybridization between species. This indicates that all species appeared in Madagascar at some point and interbred. By supplementing geological and paleoclimatic data, it can be calculated that in Madagascar, different baobab species evolved, influenced by glacial periods and rising and falling sea levels over millions of years.
The baobab species found in Africa (Adansonia digitata) and Australia (Adansonia gregorii) almost certainly left Madagascar as seeds or saplings, drifting across the ocean due to rivers swollen by storm surges. The first baobab seeds in Africa likely arrived within the last 12 million years. From there, they expanded in number, often with the help of seed-eating elephants.
By the time baobabs spread across the continent to West Africa, a cell division error occurred during the production of pollen or ovules, leading to an increase in the number of chromosomes in African baobabs (from 88 to 168). Such an increase in chromosome number is common in plants and is referred to as polyploidy. The newly polyploid baobabs may have become the dominant species in Africa, replacing previously existing species across the continent. This may have occurred over approximately 2,500 years, based on calculations of the seed dispersal rate by elephants.
The new research on the origins of baobab trees is seen as a crucial key contributing to conservation decisions and the breeding of baobab species, including those listed as endangered according to the criteria of the International Union for Conservation of Nature’s Red List.
