Systematics and evolution of the Old World Ebenaceae, a review with emphasis on the large genus Diospyros and its radiation in New Caledonia

In this review article, we provide an overview of the status of research on Old World Ebenaceae with an emphasis on the large genus Diospyros. The well-supported phylogenetic tree obtained from nucleotide sequences of multiple regions of plastid genome gave clear insights into the subfamilial classification of Ebenaceae. It supported inclusion of previously recognized genera such as Cargillia, Gunisanthus, Maba, Macreightia and Tetraclis in Diospyros. Endemic Diospyros spp. of New Caledonia have multiple origins. One of these clades has c. 21 species that are morphologically distinct and occupy different ecological niches, but they exhibit low genetic variation, leading to a lack of phylogenetic resolution. Analyses of whole plastid genome sequences did not greatly increase resolution or support for results of our previous plastid analyses. Geographical clustering of the individuals against a background of lower sequence divergence of the whole plastid genome could be due to transfer of plastid genomes during hybridization and introgression following secondary contact. However, > 8400 filtered single nucleotide polymorphisms (SNPs) from restriction site associated DNA sequencing (RADseq) confirmed species circumscriptions for this clade and produced well-supported phylogenetic relationships, pointing to an early regional clustering among populations and species. This supported allopatric speciation with respect to macrohabitat (i.e. climatic conditions) having had a role in the initial differentiation in the group. A later, more rapid radiation involved divergence with respect to microhabitat (e.g. soil preference). Although chromosome counts indicate that Diospyros spp. are consistently diploids with 2n = 30, extensive variation in genome size has been observed, which is due to an increase of repeat elements, including LTR/gypsy. In Ebenaceae, pollen is heterogeneous, and palynological synapomorphies are traced at different taxonomic levels. Several new Diospyros spp. have recently been identified and documented from India, Thailand, China, Africa and New Caledonia. Taxonomic revisions have been completed for the Australian species, and synonyms are reported for some New Caledonian Diospyros spp.