Baobabs are one of the most charismatic trees on Earth. Their cartoonishly thick trunks are noticeably exaggerated in relation to their tiny crowns, earning them the nickname “upside-down trees.” They can also live for thousands of years, contributing to their prominent place in cultural traditions and works of art.
However, its origin story remains a mystery.
There are eight species worldwide and their distribution, like the trees themselves, is unusual: one species is found in much of mainland africa, while six are in Madagascar. The last one is located far away, in the northwest of Australia.
Researchers have hypothesized that the trees originated on mainland Africa. But findings recently published in the journal Nature found that baobabs probably evolved in Madagascar, where they diversified into different species. Two embarked on ocean voyages to distant continents.
“In the case of baobabs, a very special geographical history on the island contributed to the diversity of the species,” said Tao Wan, a botanist at the Wuhan Botanical Garden of the Chinese Academy of Sciences and an author of the study.
Wan’s team sequenced the genomes of all eight baobab species to understand how the trees evolved. The team found that the common ancestor of baobabs probably emerged in Madagascar about 21 million years ago. Competition with other plants and factors such as altitude, temperature and rainfall caused the emergence of new species in Madagascar.
About 12 million years ago, two species of Malagasy baobabs reached continental Africa and Australia, where they evolved into the unique trees that grow there today. Most likely, multiple baobab seeds stowed away when vegetation was transported by the Indian Ocean Gyre, a current that circulates between Australia, southern Asia, and the eastern coast of Africa—exemplifying the “extraordinary long-term dispersal patterns.” distance” from the species, said Andrew Leitch, a plant geneticist at Queen Mary University of London and an author of the study.
Two of the Malagasy species have alarmingly low genetic diversity, indicating that they may lack the resilience needed to adapt to climate change. A third is also at risk of disappearing due to miscegenation with a cousin.
The six species of Malagasy baobab are also affected by the extinctions that have occurred in Madagascar over the last 2,500 years., mainly due to human activity. Several species of giant lemurs, which served as pollinators, were hunted to extinction a thousand years ago. And the forest growth under Madagascar’s baobabs has been lost to development.
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