Where did baobabs come from? Scientists unravel mystery of ancient trees

For millions of years, mighty baobabs have stood sentinel across three different landmasses, asking each other an existential question: Who came first?

The giant trees, with swollen trunks and squat tops, are unmistakable. Baobabs can live for more than a thousand years, acting as keystone species in dry forest environments in Madagascar, a swath of continental Africa and northwestern Australia. Known as the “mother of the forest” and “tree of life,” almost every part of the tree can be used by humans and animals, meaning they have enormous value to each ecosystem they inhabit.

Its reputation was only enhanced by the mystery surrounding its origins. Until now, science has had to make do with multiple conflicting hypotheses – the dominant theory being that they came from continental Africa. Not so, according to a study published last month in Nature magazine. A team of international academics has successfully sequenced the genomes of each of eight baobab species, examining their relationship and concluding that they originated in Madagascar.

The news comes as trees face steep decline on the island, home to six baobab species, with one of them likely to go extinct by 2080, according to the study, unless significant interventions are implemented.

Biologists have had difficulty determining the tree’s origins because no fossils of ancient baobabs or their ancestors have been discovered, explained Wan Jun-Nan, one of the study’s authors and a researcher at the Wuhan Botanical Garden in Hubei, China. The genetic data recovered from baobabs in previous studies was limited, he continued. But with the first complete genome sequence for each species, “we can tell a good story about evolutionary history,” he argued.

This story begins with the emergence of baobabs in Madagascar about 21 million years ago, before the genus (scientific name Adansonia) began to diversify, and two species arrived in Africa and Australia about 12 million years ago. This occurred well after the breakup of the “supercontinent” Gondwana, so it is likely that the baobab spread through ocean-borne seeds on floating debris caused by flash floods, according to the researchers.

The study, a collaboration between the Wuhan Botanic Gardens in China, the Royal Botanic Gardens in the United Kingdom, the University of Antananarivo in Madagascar and Queen Mary University of London, was also able to track gene flow between species of the eight types of baobab for the first time. This data, which demonstrated low genetic diversity between two species and interbreeding of one species with a more populous one, offers insights into competition between baobabs today, Wan said, and could help protect the trees of the future.

“We hope that in the future, the people of Madagascar can care for baobabs by considering them as different species, not as a whole,” he added.

Only one species of baobab is not included in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species: A. digitata, which populates continental Africa. Three species in Madagascar are threatened with extinction, and the study recommended that the IUCN recategorize one of them, A. suarezensis, from “endangered” to “critically endangered.” Climate modeling has indicated that the species could become extinct within 50 years without major intervention.

This prediction is “plausible” and “highlights the urgent need for action,” according to Seheno Andriantsaralaza, a tropical ecologist working in Madagascar.

Andriantsaralaza, who was not involved in the research, supported the call to update the IUCN status of certain Malagasy baobabs. While she described the study as “fantastic and significant,” generating “valuable” genetic insights, she cautioned that it represents “just one piece of the puzzle in understanding the evolutionary history and dispersal mechanisms of these iconic giant trees.”

The study’s modeling concluded that the range of baobab species has been declining on the island for millennia, with human-caused climate change and ongoing deforestation exacerbating the reduction and fragmentation of baobab populations in recent decades.

Andriantsaralaza said that “it is crucial to recognize that amid the challenges, there are local success stories and initiatives led by local organizations and researchers.”

She cited the conservation group Madagasikara Voakajy, which coordinates projects in the north of the island focused on protecting A. perrieri and A. suarezensis. Additionally, PEER, a USAID-supported program in which she participates, aims to empower locals to contribute to sustainable ecosystem management.

“Madagascar’s baobab forests belong to local communities who depend on natural resources to feed their families,” he added. “They should be part of the solution, not the problem.”

Wan said he hoped the research and media attention would encourage more conservation efforts for the island’s baobab trees.

While celebrating the advancement, he acknowledged the study’s limitations—only one individual per species was sequenced—though he hoped future research would expand sampling and answer other outstanding questions about the trees.

The likelihood of finding fossil evidence to confirm conclusions from the genetic data is small, Wan admitted. So perhaps these majestic trees can retain some of their mystery after all.

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