From a phylogenetic perspective, Euphorbia balsamifera, found in the arid regions of northwestern Africa and the Canary Islands, is closely related to Euphorbia adenensis, which originates from the Eritrea-Arabia region. These two species share a common ancestor that likely emerged several million years ago.
Molecular data suggest that the divergence between E. balsamifera and E. adenensis occurred during the Pliocene, a period spanning approximately 5.3 to 2.6 million years ago. This era coincides with a major episode of climate aridification in the subtropical regions of the Old World, leading to the fragmentation of forest habitats in favor of more open and arid landscapes. These new environmental conditions likely facilitated a rapid adaptive radiation of the ancestral group, meaning the emergence of several lineages specialized for arid habitats.
In this context, E. balsamifera is thought to have colonized the Canary Islands from northwestern Africa. This colonization may be explained by the "surfing syngameon" mechanism—an evolutionary hypothesis in which a flexible gene pool (or syngameon) "surfs" waves of dispersal into new territories while maintaining sufficient genetic diversity to allow rapid adaptation to novel environments.
Computer models using convolutional neural networks (a form of artificial intelligence) suggest that E. balsamifera first settled on the eastern islands (Lanzarote, Fuerteventura), before migrating westward (Tenerife, Gran Canaria).
Contrary to what one might assume, the populations in North Africa are not remnants of an ancestral continental population. Instead, they result from migratory events originating from the islands of Lanzarote and Fuerteventura. These back-colonization events likely occurred during the Middle Pleistocene, although this still requires confirmation.
This finding challenges the notion that islands merely "receive" genetic diversity from the continent. In this case, the Canary Islands actually generated new genetic diversity that subsequently spread back to the African mainland.
Ref. : Rincón-Barrado M., Villaverde T., Perez M.F., Sanmartín I. & Riina R., 2024 - The sweet tabaiba or there and back again: phylogeographical history of the Macaronesian Euphorbia balsamifera. Annals of Botany 133 : 883–903. https://doi.org/10.1093/aob/mcae001, available online at www.academic.oup.com/aob
Posted by Jean-Paul Peltier.