THE affinities between floras of widely separated regions of the world, as well as modes of dispersal of elements in these floras, have long been of interest in evolutionary and phytogeographical studies1-3. While investigating phylogenetic patterns and modes of speciation in the endemic plants of the Juan Fernandez Islands, Chile4-6, we have documented an inter-population separation (disjunction) for the plant genus Peperomia (Piperaceae) of more than 5,000 km, one of the longest known in flowering plants. Peperomia berteroana ssp. berteroana occurs only in the Juan Fernandez Islands in the Pacific Ocean, and P. berteroana ssp. tristanensis is restricted to the Tristan da Cunha archipelago in the South Atlantic Ocean. Flavonoid and morphological data suggest that plants from Masafuera, the younger of the Juan Fernandez Islands, are ancestral to Tristan da Cunha populations. We propose that long-distance dispersal by birds is the most likely cause of this wide disjunction.