Abstract/Summary

Diospyros is the largest genus of Ebenaceae and the only genus of the family found in tropical Asia. It is economically important as several species can be a source of ebony wood, such as Ceylon ebony (D. ebenum), or produce commercial fruits, such as persimmon (D. kaki). While South-East Asia has been considered one of the centres of diversity for the genus, the previous taxonomic studies were carried out at national scales and sometimes lacked access to type collections. As a result, there has been redundancy in scientific names for some species as well as widespread misidentifications. In this study, an integrated taxonomic revision of the species found in Indo-China (Cambodia, Laos, Thailand and Vietnam) was conducted by using comprehensive taxonomic information, such as multiple taxonomic accounts, all available type and non-type specimens in herbaria and online databases. Fiftyfour taxa have been lectotypified and type materials of an additional 15 taxa are in the process of formal lectotypification. Ninety-six accepted taxa have been enumerated with nomenclatural histories and synonymy, brief morphological descriptions, miscellaneous notes and distribution information. Taxonomic changes have been made including the resurrection of six taxa, the updates of four names according to the principle of priority, the synonymisation of 34 taxa and three new records for Indochina. The previous phylogenetic understanding of Diospyros had been based on 4–8 plastid markers but suffered from uncertainty in several clades and insufficient representation from South-East Asian taxa. By employing next-generation sequencing, up to 79 plastid protein-coding genes of up to 150 taxa were successfully included in the phylogenies. However, the phylogenetic resolution is not significantly improved from the previous multi-locus phylogenies. Furthermore, the relationships based on the nuclear genome have been uncertain due to the difficulties in obtaining and identifying orthologous nuclear genes in the past. In this study, we used the Hyb-Seq technique to obtain DNA sequences of up to 307 orthologous nuclear genes of around 177 taxa, to reconstruct the species trees using both multispecies coalescent and supermatrix approaches. Conflicting phylogenetic signal has been observed through nuclear gene tree discordance. Additional evidence from the cytonuclear discordance suggests that Diospyros might have undergone rapid radiation (short internal branch lengths), hybridisation and incomplete lineage sorting, and the true species tree is unlikely to be strictly bifurcating. The phylogenetic outcomes have also provided the appropriate taxonomic placements of some species complexes, such as D. siamensis and the D. ferrea complex. Overall, this research suggests that future taxonomic studies of Diospyros should be carried out using integrated frameworks including: morphological, genetic and other biological evidence.