Revisiting the Axelrod’s Hypothesis: What is the Origin of the Evergreen Sclerophyllous Oaks in the Northern Hemisphere?

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2025

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Sancho Knapik, Domingo
Martín Sánchez, Rubén
Peguero Pina, José Javier
Gil Pelegrín, Eustaquio

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Abstract

Axelrod proposed a hypothesis to explain the origin and evolution of the evergreen sclerophyllous flora in the Northern Hemisphere, suggesting an insitu differentiation of clades at low-mid latitudes during the Cenozoic. This hypothesis highlights a continuous belt of sclerophyllous vegetation that was fragmented over time due to tectonic movements and climatic changes, including cooling and drying. The genus Quercus exhibits numerous sclerophyllous species, which reach their highest diversity in the latitudes he identified. However, the evolutionary histories of the two subgenera within Quercus-the New World and Old-World clades-show distinct patterns. This review examines whether Axelrod’s hypothesis holds true for Quercus by synthesizing recent molecular phylogenies, fossil records, and biogeographic analyses. Findings reveal that while Old World oaks largely align with Axelrod’s hypothesis, the recent diversification of the tropical NewWorld oaks challenge the framework he proposed.

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Martín, R.; Sancho, D.; Peguero Pina, J.J. and Gil, E.Revisiting the Axelrod’s Hypothesis: What is the Origin of the Evergreen Sclerophyllous Oaks in the Northern Hemisphere?. Biodiversity Online J. 5(2). BOJ. 000606. 2025
AGROVOC subjects
Quercus
Adaptación al cambio climático
Vegetación

Sponsorship

This research was supported by Grant PID2022-136478OBC32 funded by MICIU/AEI/10.13039/501100011033, by “ERDF A way of making Europe”, by grant CNS2022-136156 funded by MCIN/AEI/10.13039/501100011033 and European Union Next Generation EU/PRTR, and by Gobierno de Aragón S74_23R research group. The work of Rubén Martín-Sánchez was supported by a PhD Gobierno de Aragón scholarship.

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http://hdl.handle.net/10532/7442

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