The Pacific palaeogeography of Rhizophora mangle L. (Rhizophoraceae)

The American red mangrove, Rhizophora mangle is disjunct in its occurrence between the Neotropics and an outlier in the south-west Pacific, a distribution which has been speculated upon for over a century. The species is shown to be indigenous in Tonga, the first such evidence from the outlier, with certain identification of abundantly occurring pollen in an early Holocene mangrove peat, that pre-dates the arrival of man by some 2500 years. It is suggested from review of world-wide fossil records that the species crossed the Pacific eastwards during the Eocene, facilitated by land connections resultant from low stands of sea level and before major subsidence of the Pacific plate. Then subsidence of the Pacific plate caused local extinctions on islands of the central and eastern Pacific as they periodically submerged, the species not able to recolonize from either refuges west of the Andesite line or America due to loss of land connections and its poor dispersal capability.