Tracing the biogeographic history of the world's most isolated insular floras

A new study reveals that the New Zealand Sub-Antarctic Islands, one of Earth's most isolated regions, have maintained high biological connectivity with southern landmasses like Australia, New Zealand, and South America since the Miocene. Contrary to expectations, long-distance dispersal—not tectonic vicariance—has been the primary mechanism for plant colonization, facilitated by eastward-moving marine and wind currents, short-term weather systems, or bird dispersal. Phylogenetic reconstruction, divergence time estimation, and Bayesian biogeographic analyses of seven vascular plant lineages show that most species diverged during the Plio-Pleistocene, with crown ages predating the Last Glacial Maximum, indicating these islands acted as biodiversity refuges. The findings highlight their dual role as both refugia and sources of (re)colonization, emphasizing the urgent need for conservation planning in this remote sub-Antarctic region.

Aguado‐Lara, Á., Sanmartín, I., Le Roux, J. J., García‐Verdugo, C., Molino, S., Convey, P., Jansen van Vuuren, B., & Mairal, M. (2025). Tracing the biogeographic history of the world’s most isolated insular floras. Journal of Systematics and Evolution, 63(4), 952–973. Portico. https://doi.org/10.1111/jse.13170