Dispersal across Wallace's Line: A case study in Endiandra

Floristic exchanges between Oceania and tropical Asia have significant asymmetrical characteristics. Many groups of plants have dispersed southward from Asia to Oceania, whereas a northward dispersal from Oceania to tropical Asia (i.e., the "Dacrycarpus pattern") is rarely reported. The genus Endiandra (Lauraceae) is distributed from tropical Asia to Oceania, with higher species richness in Oceania, so it can contribute to our understanding of paleotropical biogeography.

We sequenced plastid genomes (plastomes) of 69 species using an herbariomic (genome skimming) approach, with 48 plastomes reported for the first time. We also reconstructed a phylogenomic tree, estimated divergence times, analyzed ancestral areas, and studied the biogeographic history of the genus.

Our well-resolved phylogenomic tree depicts Endiandra as a paraphyletic group in which two Australian species of Beilschmiedia are nested. Dating analysis indicated that the stem and crown ages of the genus are 51.21 and 45.69 million years old, respectively. Ancestral area reconstruction indicates that the genus originated in Oceania and that several independent dispersal events across Wallace's Line shaped its modern distribution.

The geological history and environmental changes in the Neogene likely facilitated the dispersal of Endiandra. However, the inferred dispersal patterns proved more complicated than the classic "Dacrycarpus pattern", helping improve our understanding of the paleotropical biogeographic history of plants.